Sea Urchin Aquaculture - the National Sea Grant Library

Transcription

American Fisheries Society Symposium 46:179–208, 2005
© 2005 by the American Fisheries Society
Sea Urchin Aquaculture
SUSAN C. MCBRIDE1
University of California Sea Grant Extension Program,
2 Commercial Street, Suite 4, Eureka, California 95501, USA
Introduction and History
The demand for fish and other aquatic products has increased worldwide. In many cases,
natural fisheries are overexploited and unable
to satisfy the expanding market. Considerable
efforts to develop marine aquaculture, particularly for high value products, are encouraged
and supported by many countries. Sea urchins,
found throughout all oceans and latitudes, are
such a group. After World War II, the value of
sea urchin products increased in Japan. When
Japan’s sea urchin supply did not meet domestic needs, fisheries developed in North America,
where sea urchins had previously been eradicated to protect large kelp beds and lobster fisheries (Kato and Schroeter 1985; Hart and
Sheibling 1988). As North American fishery
stocks were reduced, sea urchin fisheries expanded in South America (Vasquez 1992). In
Europe, fishery stocks have also been depleted
and aquaculture systems have been developed.
Sea urchins have been important since the 19th
century for developmental research, and largescale laboratory systems for maintenance of
broodstock are found in many universities (Leahy
et al. 1978, 1981). Many species of sea urchins
are currently fished or cultured (Table 1).
Sea urchins are an unusual candidate for
aquaculture as they are harvested for their gonads. Both male and female sea urchin gonads
are consumed, usually uncooked, but some are
salted, pickled, or made into paste. Processed
sea urchin gonads remain one of the most valuable seafood products valued over US$100/kg
on wholesale markets (www.nmfs.gov/owstrade). Whole, live sea urchins, or processed
gonads are sold in Asia, Europe, and North and
1
E-mail: scschlosser@ucdavis.edu
South America. The correct color, texture, size,
and taste are factors essential for successful sea
urchin aquaculture. There are many reasons to
develop sea urchin aquaculture. Primary
among these is broadening the base of aquaculture, supplying new products to growing
markets, and providing employment opportunities. Development of sea urchin aquaculture
has been characterized by enhancement of wild
populations followed by research on their
growth, nutrition, reproduction, and suitable
culture systems.
Sea urchin aquaculture first began in Japan in 1968 and continues to be an important
part of an integrated national program to develop food resources from the sea (Mottet 1980;
Takagi 1986; Saito 1992b). Democratic, institutionalized, and exclusive control over fishing
grounds, including some aquaculture rights,
favor and support fishery enhancement and
aquaculture activities to increase production
in Japan’s coastal waters. An extensive program
of research, education, and extension services
support the national program, as Japanese consumption of seafood is the highest per capita
in the world.
Sea urchin aquaculture began with management of fishery resources where adult animals
were transplanted to more favorable habitats.
This fishery management tool led to sea urchin
aquaculture research. These activities occurred
mainly in Kyushu, Tohoku, and Hokkaido, the
regions with sea urchin fisheries. The objective
was to increase gonad production and supply
high value products to a human population
where the standard of living was continuing to
improve. Sea urchin fisheries in Japan began
showing signs of depletion in 1967 and efforts
to culture sea urchins to supplement natural
populations began in the early 1960s (Saito
1992a, 1992b). To meet the demand for sea ur179
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Table 1.—Species, range, and countries where the species is cultured or where research projects are currently in process.
Species
Family
Range
Country
Anthocidaris crassipina
Heterocentrotus pulcherrimus
Pseudocentrotus depressus
Strongylocentrotus intermedius
Echinometridae
Strongylocentrotidae
Toxopneustidae
Japan
Japan
Japan
S. nudus
Lytechinus variegatus
Loxechinus albus
S. droebachiensis
Toxopneustidae
Echinidae
S. franciscanus
S. purpuratus
Heliocidaris erythrogramma
Evechinus chloroticus
Tripneustes gratilla
Echinometridae
Echinometridae
Toxopneustidae
mid-Honshu to Kyushu, South Japan
North Honshu to Kyushu, South Japan
Tokoyo Bay to Kyushu, South Japan
Tohoku to Hokkaido, North Japan,
Korea, China, Russia (Kamchatka)
Sagami Bay to Hokkaido, North Japan,
Korea, China, Russia (Kamchatka)
Subtropical–Tropical Americas
South Peru, Chile
Circumpolar and south to Washington,
New Hampshire, and Norway
Alaska to Baja California, East Pacific
Alaska to Baja California, East Pacific
Australia
New Zealand
Indo-Pacific
T. ventricosus
Paracentrotus lividus
Toxopneustidae
Echinidae
Psammechinus miliaris
Echinidae
Japan
Japan
USA
Chile
USA, Canada
USA, Canada
USA
Australia
New Zealand
Japan, Taiwan,
and Philippines
Atlantic South America to Gulf of Mexico USA
North Atlantic–Mediterranean
France, Belgium,
Italy, Ireland,
and Israel
North Atlantic–Mediterranean (Norway
and Iceland to Morocco)
Scotland
chin roe products, the Japanese government supported basic and applied research on the feeding habits, reproductive cycle, and environmental requirements. Initial research led to additional
and ongoing studies of nutrition, environmental control, culture systems, and control of the
reproductive system (Imai 1978; Agatsuma
1998).
Since 1970, approximately 55 prefectural
hatcheries have produced small sea urchins for
cooperative units, which have collective rights
over local aquatic resources. The production
laboratories are responsible for supplying sea
urchins to cooperative associations. The cooperative associations manage the land-based
nursery units and restocking programs in suitable coastal habitats. The coastal areas are managed by predator removal, addition of algae,
and sometimes habitat improvements, until
harvest, usually 2 to 5 years later. More recently,
some cultured sea urchins are reared in cage
systems at high density and fed cultured seaweed until they are large enough for marketing (Mottet 1976, 1980; Doumenge 1990; T.
Horii, National Research Institute of Fisheries
Science, Nagai, Japan, personal communication). Large-scale aquaculture of sea urchins
to harvest size is not popular in Japan, and
most cultured sea urchins are released as juveniles (Table 2).
Japanese demand for sea urchin products
increased dramatically during the 1980s and
domestic production was able to supply about
one-half the consumer demand. This led to
rapid development and expansion of sea urchin
fisheries in North and South America. Early
warnings from fishermen and resource managers warned of fishery declines. Aquaculture research was rapidly initiated in many countries.
Sea urchin aquaculture in countries with fisheries followed the same pattern as that seen in
Japan during the 1960s. Fishermen and scientists initially worked with sea urchins from the
fishery populations and developed methods
and diets to enhance gonad production. These
studies included holding sea urchins in suspended cages or on the sea floor and transplanting urchins to habitats with more natural algal
food. Today, sea urchin aquaculture research
often utilizes sea urchins collected from the
ocean in laboratory studies.
In Europe, there is also a long history of
sea urchins used as food. Sea urchins are eaten
whole and fresh in southern Europe, in contrast
to the processed roe products popular in Japan.
Sea urchins are sold through the fisheries sec-
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SEA URCHIN AQUACULTURE
Table 2.—Production of sea urchin seed for release and aquaculture in Japan for fiscal year April 1999 to
March 2000 (data from T. Horii, National Research Institute of Fisheries Science, Nagai, Japan,). The number
of product organizations that cultured or cooperative fishery associations that released each species and
areas where species were released are also shown. The number of seeds produced is the total for the year
and the number released is the actual amount released during this fiscal year. (org. = organizations, n.a. =
not applicable)
Species
Tripneustes
gratilla
Production
type
Seed
produced
size (mm)
mean range
release
11 1–25
aquaculture n.a.
Pseudocentrotus
depressus
release
aquaculture
Heterocentrotus
pulcherrimus
release
aquaculture
Strongylocentrotus
intermedius
release
aquaculture
S. nudus
release
aquaculture
# of # of seed
org. produced
Seed
released
size (mm)
mean
range
3
136,000
14
3–50
# seed
released
# of
org.
# of
areas
99,000
3
20
16
8
3–29
3–17
11
2
9,460,000
152,000
12
n.a.
3–30
3,739,000
79
25
9
10
3–15
8–12
3
1
590,000
10,000
11
n.a.
3–27
489,000
10
47
11
8
18
11
2–49
3–22
6–46
6–31
28
2
10
3
64,985,000
6,696,000
6,718,000
366,000
12
n.a.
18
n.a.
2–106 57,895,000
94
486
7–50
11
302
tor network by auction. Cultured sea urchins
could be sold at a fixed price, which would require management of harvesting, production,
and shipping. Much of the European sea urchin
supply is not eaten locally and the diversity of
regional preferences must be considered for
industry expansion (Birulés 1990).
South Americans, particularly in Chile,
also enjoy fresh whole sea urchins. Chile currently produces 50% of the world’s harvested
sea urchins with approximately 10% of the production consumed in Chile (Roa 2003). In
North America, approximately 5–10% of production from California fisheries is sold domestically. These markets, though small, are
expanding. Most sea urchin roe, called uni in
Japan, is sold at sushi bars as topping for
cooked rice wrapped in seaweed. People seem
to either love or hate the taste of uni, which
has been described as “ocean bubble gum,”
better than caviar, tastes like custard or a mild
pate. It is not to everyone’s taste, but it is a
delicacy and worth a try.
Countries now looking to sea urchin aquaculture for stock enhancement of depleted fisheries include Canada, Chile, New Zealand, and
the United States. Sea urchin aquaculture in
these countries and others is repeating the pattern of the early Japanese research. Enhance-
7,120,000
ment of wild populations with supplemental
feeding, transplanting of sea urchins to favorable habitat, and research scale hatcheries indicate aquaculture production of sea urchins is
biologically possible, but the economics are
unclear. Providing a consistent supply of a quality product is essential for the sea urchin roe
market. The proper balance between identifying market potential, research priorities, and the
eventual production of a consistent supply of a
superior product are among the criteria essential for successful aquaculture of sea urchins.
Some of these criteria have been met for sea urchins, but many remain to be explored.
Taxonomy and Anatomy
Sea urchins are members of the Phylum Echinodermata. Sea urchins are entirely marine and
free-living. Most edible sea urchins are adapted
for life on hard, benthic surfaces and generally
live in areas with algal food available. They tend
to live in shallow waters, usually from mid to
low intertidal zones to depths of about 50 m.
Commercially important sea urchins are
spherical but slightly flattened and with movable spines. Each spine fits neatly into a socket
joint in the shell and can be used to move vertically and horizontally. Tubular feet or podia are
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found in rows alternating with the spines and
have well-developed suckers for attachment.
Podia are also sensitive to chemicals and touch,
absorb oxygen, catch drifting algae for food, and
keep the body clean. The spines are controlled
by muscles and are used for protection, to capture and hold food, and for locomotion. Healthy
sea urchins can right themselves using the spines
and podia. In between the spines and also attached to the calcified body wall or test, are
pedicellaria, small, stalked, appendages used for
defense, capturing small prey or to clean the body
surface.
The body is radically symmetrical. Externally, sea urchins are extremely colorful due to
skin pigments and can be pale yellow, green,
pink, purple, red, or black. Internally, the gonads are also colorful due to carotenoid pigments and desirable gonad colors are yellow
and orange. Undesirable gonad colors are white,
tan, brown, black, or green.
The sea urchin body has an oral (bottom)
and aboral (top) surface. The aboral surface contains the anal region where excretory products
and gametes are released and water vascular
system is controlled (Figure 1).
The spherical body surface covered with
movable spines comprises 50% of the live sea
urchin body weight. The oral surface includes
the mouth, which can be protruded, a peristomal
membrane allowing movement of the mouth,
short spines, and podia. The mouth or “Aristotle’s lantern,” named in honor of the Greek
naturalist and philosopher, is effective at tearing algae into manageable pieces. It is composed
of five calcareous plates and teeth that are controlled by muscles. The mouth leads to the tubular digestive system, which is intimately connected to the five gonads by mesenterial and
hemal strands. Between the five gonads are
structures of the water vascular system. When
sea urchins are harvested, gonads must be 10–
14% of the body weight for successful processing and marketing.
Reproduction in sea urchins is a complex
process involving nutrient accumulation in the
gonads, transfer of the accumulated nutrients
from nutritive cells to gametogenic cells, storage of the gametes, and spawning either through
a series of dribbling releases or a mass spawning at one time (Pearse and Cameron 1991;
Walker et al. 2001). Gonad production in edible
Figure 1.—Internal and external anatomy of a sea
urchin. Upper drawing shows external spine attachments, pedicellaria, and tube feet. The mouth and
teeth (Aristotle’s lantern) and internal digestive system are shown in the lower drawing. The five gonads of sea urchins can be seen in the upper drawing (from Mottet 1976).
sea urchins progresses through reproductive
stages that include gonads in the mature, spent,
regenerating, growing, and premature condition. Commercial harvest is optimal when the
gonads are in the growing or premature stage.
Gonads in this condition contain a majority of
nongerminal, nutritive cells filled with glycogen, protein, and lipid. They are firm, have good
color and texture, and are large. Gonads are
equally large or larger during the mature phase,
but moisture content is higher, the texture is very
soft, and the gonads tend to fall apart. Gonads
that are spent or regenerating are too small, often very dark, and are not marketable (Figure
2a, 2b).
Aquaculture of sea urchins has developed
partly because the annual reproductive cycle
limits availability. The mature and growing seasons each last about 1 to 6 months, depending
on the species. Seawater temperature, food
availability, photoperiod, and sea urchin density effect timing of the annual reproductive
cycle. Gonad production in sea urchins is measured by the gonad index. Throughout this pa-
a
b
Figure 2.—Adult red sea urchin Strongylocentrotus
franciscanus with (a) low gonad index of 2% and (b)
with full gonads and a gonad index of 20%.
per, unless otherwise stated, gonad index is
given as a percentage [(wet gonad weight/
whole animal live weight) × 100].
Some innovative, intermediate forms of
aquaculture have been developed for sea urchins
to increase productivity of wild populations.
Intermediate Stages of
Aquaculture—Transplanting
Adults and Collecting Juveniles
In Japan, reduction of fishery stocks resulted in
activities focused on maintaining sea urchin
populations and increasing production from
populations in less favorable areas. Transplants
of adult sea urchins were conducted under the
assumption that some populations were limited by the amount of food or habitat available.
Sea urchins from overgrazed areas devoid of
algae were moved to areas with more food available. These sea urchins were of poor quality
with virtually no gonadal development and
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could not be harvested as part of the commercial fishery. The transplanted sea urchins were
moved when the gonads were in the growing
stage of their annual reproductive cycle. With
sufficient food, these urchins were harvested 3
months later. In some cases, the transplanted sea
urchins were fed fish or algae at the new site.
The main species involved in transplants were
Pseudocentrotus depressus and Strongylocentrotus
pulcherrimus in southern Japan and S. intermedius and S. nudus in the north (Saito 1992a).
Mortality was generally low, 1–2%, and as a result many fishing areas depended heavily on
this method. Approximately 20 metric tons (mt)
of sea urchins had been transplanted before 1969
(Takagi 1986). Transplanting of wild sea urchins
remains an important fishery management tool
in Japan.
A field test to examine transplanting sea
urchins was completed in California in 1997.
Strongylocentrotus franciscanus measuring 25–
70 mm in test diameter were transplanted from
an area devoid of algae to dense kelp beds. Fishermen and scientists moved approximately
34,000 urchins. The transplant site was 0.24 ha
(0.6 acres) and had a standing population estimated at 2,100. The area where the urchins were
collected was the same size and had about
42,000 sea urchins. After 1 year at the new site,
many sea urchins have grown to nearly 90 mm,
the legal size for harvest. A conservative estimate of survival, not taking into consideration
animals that have moved from the study site, is
60% of the original transplants. The transplant
was cost effective at US$3,500 or $0.10 per urchin and the high recapture rate was encouraging for the future of the California sea urchin
industry (Schroeter and Steele 1998).
In Japan, the next intermediate phase was
collection of naturally set larvae. The first experimental collection of larvae was completed
in 1967 with P. depressus. Early larval collectors
used nylon threads for settlement. Other inwater and benthic larval collectors were developed and included transparent polyvinyl chloride (PVC) plates with a corrugated surface and
enclosed gravel beds (Takagi 1986). After 8
months, an average of 1,200 sea urchins measuring 2 mm in test diameter was harvested
from the in-water collectors. The small urchins
were moved to suitable habitat or prepared
gravel beds (Mottet 1980). Small urchins tended
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to fall off the in-water collectors, and predation was a problem in the benthic systems. Collection of natural seed in Hokkaido was not
pursued due to fluctuation in the supply of
natural seed. Most cooperative associations
carried out some form of adult or juvenile transplanting or collection between 1967 and 1984.
Cultured sea urchin seed production began at
the national level in 1984.
In California, transplants of juvenile S.
franciscanus with a mean size of 25 mm in test
diameter were completed between 1992 and 1998
at four sites. Survival at two sites was greater
than 50%, and at the other two sites, it was less
than 10% after 1 year. Survival after 5 years was
between 6% and 11%. About half the survivors
were large enough for harvest. The work was not
continued because there was no source of commercially available sea urchins for additional
stock enhancement (Dixon et al. 1998).
In Ireland, Paracentrotus lividus has been
fished for decades with minimal fishery management. Transplanting of animals from
grounds with poor growth rates to areas with
more food available is done with subcommercial size animals, 35–45 mm. In general, these
animals reach good market size and condition
after 1 year. This type of work has been carried
out by fishermen with little data available, but
anecdotal evidence shows small urchins (10
mm) grow to 50+ mm in 2–2.5 years (Leighton
1995). Natural seed collection trials based on
techniques used in Japan collected P. lividus and
Psammechinus miliaris juveniles. The results were
encouraging but have not been continued
(Moylan 1997).
The next phase of in-water sea urchin
aquaculture is feeding seaweed to animals enclosed in cages or on the sea floor. In Japan, the
United States, Canada, Scotland, Ireland, and
Mexico, experimentation with this type of intermediate culture has been completed but it
is not used on a commercial basis. Enclosures
on the sea floor near Southern California kelp
beds were used to feed groups of S. purpuratus
and S. franciscanus. Some groups were fed with
kelp; Macrocystis pyrifera and others were unfed.
Gonad production was significantly increased
in groups that received supplemental feeding
(Leighton and Johnson 1992). This project was
expensive and cumbersome. Gonad production
can be enhanced quickly, but in California and
Mexico, ownership and environmental modifications of the sea floor are not legal and associated issues of multiple use of coastal areas have
not been addressed (Tegner 1989).
Development of
Sea Urchin Aquaculture
Sea urchin rearing developed in several locations for a variety of reasons. In university laboratories, holding adult sea urchin broodstock,
usually S. purpuratus, for embryology and toxicology research is widespread. The sea urchin
embryo is important because of the ease of handling and observing early development. Culturing a variety of sea urchin species for fishery
production enhancement has been practiced in
Japan since 1968. More recently, aquaculture of
sea urchins for food production is under intense
research in Canada, the United States, Mexico,
Chile, Scotland, Belgium, France, Ireland, Norway, Israel, New Zealand, and Japan. Very recently, research projects have begun in Australia, China, and the Philippines.
Japan
Extensive studies of naturally setting S. intermedius larvae resulted in rearing the small urchins in land-based hatcheries until they were
large enough for outplanting (Kawamura 1973).
Aquaculture of sea urchins was first conducted
in the Yamaguchi Prefecture in 1968 with P.
depressus and H. pulcherrimus and was soon followed by work with H. crassispina. During these
studies, the phytoplankton Chaetocerous gracilis
was used successfully to feed the larvae. The
first cultured sea urchin seed of 10-mm test diameter were stocked in prepared gravel beds
on the sea floor in 1974. Survival for the first year
was between 65% and 75% (Takagi 1986).
In the early 1980s, projects were organized
at the Hokkaido Institute of Mariculture to develop techniques of mass seed production of
S. intermedius under a 3-year plan. The national,
prefectural, local governments and the local
cooperative association contributed to the program. Generally, the national government
funds about 50%, the prefectural government
about 25%, and the local government and cooperative association provide the remaining
25%. There are regulations for administration
of the research station, hatchery, and nursery.
Profits to the program come from sales of the
sea urchin seed to fishermen and cooperative
associations that release them to fishery
grounds. Often the facility does not earn a
profit, but as long as the cooperative fishery
association earns a profit from fishery harvest
or sales to fishermen, the government continues to support the facility.
The Hokkaido Experimental Fish Station
and its associated sea urchin culture program
has been especially important since 1989 when
Japanese fishery production dropped below
20,000 mt. With foreign imports and low domestic harvest, the national government policy continues to support this program. Production of
cultured sea urchin seed expanded rapidly. In
Hokkaido, 8 million S. intermedius and S. nudus
seed were produced in 1986 and 30 million in
1989. The 1989 sea urchin seed production was
70% of the national total. The remainder of the
sea urchin seed production was southern species (Saito 1992b). In 1989, there were 17 sea urchin hatcheries and 27 in 2000 with annual production of 100 million in the 10–20-mm size
range (Y. Agatsuma, Tohoku University, Aoba,
Japan, personal communication)
Some new sea urchin hatcheries were constructed, and some abalone hatcheries were converted to sea urchin culture. The objectives of
the program were to collect wild broodstock,
cultivate planktonic algae to feed the larvae, rear
the planktonic sea urchin larvae, and grow the
urchins to a size suitable for release to appropriate habitat.
The technique of mass seed production had
been developed at southern hatcheries prior to
the Hokkaido expansion. Broodstock are collected from the wild populations when they are
mature. Broodstock management is not well
developed, but water temperature, food availability, and photoperiod have been studied in
southern species. Reproductive development
of Pseudocentrotus depressus and Hemicentrotus
pulcherrimus (Yamamoto et al. 1988) and
Anthocidaris crassispina (Sakairi et al. 1989) is
determined by temperature, not photoperiod.
Spawn induction is done by removing the
mouthparts and inverting the sea urchins over
a 300-mL beaker containing seawater filtered
through 1-m mesh. The ova leave the urchin via
185
the gonoduct and gonopores and are collected
at the bottom of the beaker. Males are inverted
over Petri dishes and the sperm is collected
“dry” (that is without mixing in seawater). Fertilization is done by mixing 1 mL of concentrated
sperm with 50 mL of seawater and mixing this
with the eggs from one female. After fertilization, the entire mixture is diluted to 5 L.
Fertilization is assessed every 30 min when
the eggs are washed to remove excess sperm and
prevent polyspermy. This continues for 2.5 h. The
fertilized eggs are then further diluted to 20 L,
and the eggs are left undisturbed for 20 h or until the larvae hatch out. The hatched out larvae
or dipleurula do not increase in size until they
are able to feed, about 3 or 4 d later. The feeding
pluteus shows complete gut development and
a single pair of arms in early stages and four arms
in later stages. The pluteus continues to add arms
as the rudiment of the juvenile sea urchin develops inside the larva. The echinoplutei is the final stage before settlement and metamorphosis.
a
b
Figure 3.—Larval stages of Strongylocentrotus
purpuratus. (a) 3 d pluteus or nonfeeding larvae. (b)
23 d echinopluetei larvae with rudiment of juvenile
sea urchin visible.
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Larval development takes 3 to 4 weeks in the
hatchery, depending on the seawater temperature and species (Figure 3a, 3b).
Larvae are cultured in 600-L flow-through
tanks receiving 1-m filtered seawater and are
gently aerated. The incoming water is introduced
to larval rearing tanks from a header tank where
temperature is maintained at 18°C. Five larval
tanks receive water from one header tank. Water
enters the larval tanks at the bottom and exits
through a centrally placed column with a mesh
of 50, 90, or 150 m, depending on the size and
age of the larvae. Larval density is 1–2 larvae/
mL. Batch culture of Chaetocerous gracilis are fed
to the sea urchin larvae, providing 5,000 cells/
mL/d, initially, and 20,000 cells/mL when larvae reach the eight-arm + rudiment stage.
Heteroshigma akashiwo are also fed to the larvae at
500 cells/mL and 2,000 cells/mL at the beginning and end of larval rearing. Other algae that
have been tested, but are not widely used are
Dunaliella salina, Monochrysis lutheri, and Phaeocaytylum tricornatum (Naidenko 1983). Water flow is
also increased during larval culture. Approximately 60–68% survive the larval rearing process,
and of these, 50% survive settlement and metamorphosis to become juveniles (Saito 1992b).
Larvae are ready for settlement and metamorphosis at the eight-arm echinoplutei stage
when the rudiment is approximately 300–350
m in diameter, depending on the species. Another indicator of larval competence is the ability to bend the arms, and podia may occasionally be seen protruding from the larvae. Settlement is induced using the single-celled Chlorophyte Ulvella lens (Saito 1992b) or the diatom
Navicula ramosissima (Ito et al. 1987) that have been
cultured on vinyl wavy plates. Ulvella lens is successfully mass cultured as food source for abalone, Haliotis spp., and sea urchins. It releases
spores that attach to surfaces on a permanent
basis and serve as a food source. Ulvella lens reduces the high costs of diatom culture for the
early nursery phase in sea urchin culture.
The plates with cultured U. lens or N.
ramosissima are held in racks of 24 plates in 5-m
rectangular tanks. The newly settled sea urchins
are held in these large tanks until they reach 5
mm in test diameter, approximately 3–4 months
later. Sometimes soft algae such as Ulva lactuca
are added to tanks where small urchins are
settled on the wavy plates (Figure 4a, 4b).
a
b
Figure 4.—(a) Juvenile Strongylocentrotus intermedius
rearing tanks at the Shikabe hatchery in Japan,
showing the wavy plate inserts. (b) close-up of
young sea urchins on the wavy plates.
The next nursery phase is removal of the
small urchins from the wavy plates and transferring them to baskets (65 × 65 cm), which are
suspended in the 5-m tanks or in long-line systems in the sea. The small sea urchins are then
fed kelp Laminaria japonica, the terrestrial knotweed Polygonum sachaliense, or a prepared diet
until they reach 15–20 mm in test diameter about
6 months later.
Sea urchin seed is released when they are
15 mm or larger in test diameter and are approximately 1 year old. If seed is held in landbased systems with heated water, 15 mm seed
may be released after 5 months of rearing. The
seeds are released by broadcasting them from
fishing vessels over suitable habitat. After 1 year,
survival of the seed averages 40%. Predation is
usually minimal on seed 15 mm or larger as
predators are removed from the release sites
(Miyamota et al. 1985). Cultured seed of S. intermedius reached 40 mm and had a 37.8% sur-
vival (Omi 1987) compared to wild S. intermedius, which took a minimum of 5 years to reach
60 mm (Fuji 1967). Cultured seed of S. intermedius grew faster than natural populations for the
first 14 months and then growth rate decreased
and was lower than native stock after 3 years
(Agatsuma and Momma 1988). In recent years,
sea urchin seeds have been produced for release
to coastal areas with and without existing populations and for culture to adult or market size.
In addition to research directly applicable
to sea urchin culture, a wealth of research has
examined aspects of sea urchin biology and ecology that are often used by current aquaculture
researchers. Key papers examine reproductive
cycles, energetics of growth and ecological relationships (Fuji 1967), and population modeling,
habitat requirements, and energy needs of sea
urchin populations (Fuji and Kawamura 1970a,
1970b). It is important to note that despite this
huge effort, Japanese fishery harvest has continued to decline. Annual harvest for the last 10 years
has been between 10 and 15 mt. The cause of the
decline is unknown, but reduced food availability, decreases in juvenile recruitment, and fishing pressure must play a role.
Europe
Europe is a valuable market for aquaculture
products and sea urchins have been harvested
for thousands of years from many nearshore
areas. Currently, no commercial aquaculture
production of sea urchins occurs in Europe, but
sea urchin research is at an exciting stage. Aspects of the biology and culture parameters of
Paracentrotus lividus are well documented and
Psammechinus miliaris is under investigation.
France
In France, natural sea urchin fisheries collapsed
in the 1970s (Southward and Southward 1975)
leading to development of a recirculating sea
urchin culture system (Le Gall 1990; Blin 1997;
Grosjean et al. 1998).
Larval diets and culture were studied in
detail by Fenaux et al. (1985a, 1995b). A small
scale flow-through larval rearing system was
developed using a haptophycean flagellate,
Hymenomonas carterae, as food. This successful
method is modeled after the Japanese larval
187
rearing system. Understanding larval development and response to food quantity and quality contributed significantly to development of
sea urchin culture systems in France (Fenaux et
al. 1988, 1994; Strathmann et al. 1992). Later work
by Fenaux et al. (1994) showed P. lividus reaches
16 mm after 1 year of culture on optimal diets
compared to 12.3 mm reported by Le Gall and
Bucaille (1989) in heated seawater. Both of these
growth rates compare well with fishery calculations (Turon et al. 1995).
The recirculation system developed by Le
Gall and Bucaille (1989) has been used and refined to culture Paracentrotus lividus from fertilization to harvest. The system utilizes one
area for spawning, larval and algal cultures, and
a separate rearing system for P. lividus from
settlement and metamorphosis to adult marketsize animals. Spawning is induced with potassium chloride (KCl); fertilization is checked after 4 h at 20°C. Fertilized eggs are placed in 200L tanks at a low density (250 larvae/L) for the
duration of larval culture. Larvae are fed
Phaeodactylum tricornatum once a day with 600
mL of a 10 × 106 cells/mL concentration. The
larval culture system is maintained on a 12/12
photoperiod with gentle mixing from aeration.
When 80% of the larvae are ready to settle, they
are transferred to the pregrowth portion of the
rearing system. Transfers of larvae are done
using 10-m screens to prevent larval arms from
entering the mesh and breaking.
The pregrowth area contains sieves with
500-m screens. The early postmetamorphic stage
lasts about 8 d when the young sea urchins do
not feed. As the mouth and digestive system
reorganize, fresh Enteromorpha linza is fed to the
sea urchins. The sieves are cleaned weekly and
the animals are sorted and graded monthly.
Animals larger than 5 mm are transferred to 1mm sieves.
When P. lividus reach 10 mm in test diameter, they are cultured in baskets until they reach
market size of 40 mm. Sea urchin growth in baskets submerged in shallow troughs takes approximately 2.7–3.5 years. When the sea urchins
reach 40 mm, some are prepared for harvest by
a 1- to 2-month period of starvation followed
by feeding of kelp, Laminaria digitata, or a prepared diet. The remaining adult P. lividus are
conditioned for spawning. These individuals
are held at 18–20°C and at either a 12/12 photo-
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period or in complete darkness. This system
provides mature P. lividus year round. For complete description of this system, see Grosjean
et al. (1998) (Figure 5).
The success of this system is encouraging,
and most likely, the research group will continue to improve and refine it. This recirculating system has also been tested in other areas
of the world (Blin 1997; Fernadez 1998).
An important factor that may influence
growth in the recirculating system is accumulation of ammonia, nitrate, or nitrite. Echinoids
excrete urea. In an important study (Basuyaux
and Mathieu 1999), the ammonia and nitrate
tolerance of P. lividus was measured in 20-L static
tanks with the test solutions changed daily.
Weight gain was used to determine the effects
over 15 d. The safe ammonia level determined
for P. lividus was 1 mg N-NH3–4/L (or 0.045 mg
N-NH3/L) and a slight toxicity was found at 5
mg N-NH3–4/L (or 0.226 mg N-NH3/L).
Behavior was used to test sublethal effects
on four species of sea urchins to ammonia concentrations between 12.5 and 100 mg NH4Cl/
L (Lawrence et al. 2003). Tube feet were more
sensitive than spines or the Aristotle’s lantern,
probably due to their higher permeability. Tube
feet functions include respiration, feeding, and
locomotion. A decrease in their activity would
have a deleterious effect on the capacity for gonad production and may explain the reduced
growth in P. lividus found in Basuyaux and
Mathieu (1999).
Scotland
In Scotland, where no fisheries exist, Psammenchinus miliaris has been identified as an edible sea urchin with good potential for aquaculture. Mass rearing of P. miliaris was successful using culture methods developed for
Paracentrotus lividus (Kelly et al. 2000). Larval
growth and survival was optimal using
Duniella tertiolecta and low larval-rearing densities of 1 larvae/mL.
Small (1-mm test diameter), cultured
Psammenchinus miliaris grew equally well when
fed a prepared salmon diet or Ulva lactuca. The
small urchins grew to 8 mm in test diameter in
6 months. Mortalities were 18.7% in the U.
lactuca and 37.4% in the prepared diet treatment.
Morphologically, P. miliaris fed U. lactuca had
longer spines and a more flattened test compared to those fed the prepared diet (Cook et
al. 1998). High stocking density (four individuals/L) compared to lower stocking density (two
individuals/L) were significantly smaller after
6 months. Mean initial size was 9-mm test diameter and final size was 14 and 15 mm for high
and low stocking densities, respectively (Kelly
2002). These studies of juvenile P. miliaris suggest more research is needed for diets that enhance somatic growth of juvenile sea urchins.
Ireland
Figure 5. —European sea urchin culture system from
Grosjean et al. (1998). This completely enclosed and
recirculating system has been successful used to culture several generations of the European sea urchin
Paracentrotus lividus.
Culture research in Ireland since the decline of
the fishery (Byrne 1990) has focused on larval
and early juvenile growth. The violet sea urchin Paracentrotus lividus is spawned by peristomal injection of 0.5 M KCl. Flow-through and
static culture systems were compared with significantly greater larval survival in the static (80–
90%) compared to the flow-through (1%) systems. Experiments testing various algae resulted in a larval culture system using 500-L
batch cultures that were fed a haptophycean
flagellate, Hymenomonas elongata. Larvae are
stocked at 1 larvae/mL, and each tank is lightly
aerated with one air stone near the bottom of
the tank. Temperature is maintained between
21°C and 24°C. Seawater introduced to the larval rearing tanks is filtered to 10 m. Larval sea
urchins are fed H. elongata in excess daily or
every other day. Microalgae is fed at 5,000 cells/
larvae during the four-arm stage, 8,000 cells/
larvae for the six-arm stage, and 12,000 cells/
larvae for the eight-arm stage. Larvae are removed from the culture tanks every 2 or 3 d,
collected on 10-m sieves, and placed in a clean
tank. Larvae are generally ready to settle in 14–
16 d (Leighton 1995).
Norway
University research has focused on spawning,
larval rearing, and gonad enhancement. Local
broodstock of the green sea urchin S. droebachiensis are spawned and reared at 10°C. Larvae are fed supplemented Dunaliella tertiolecta
and reared in a modified, flow-through system
following the Japanese method. All work is currently experimental (N. Hagen, Bodø University, Bodø, Norway, personal communication)
Israel
Paracentrotus lividus has been culture for 4 years
at the National Center for Mariculture in Eilat,
Israel (M. Shipgel, National Center for Mariculture, Eilat, Israel, personal observation) Spawning and larval rearing are done according to
Leighton (1995) in winter months when ambient seawater temperatures are 20–21°C. Settlement of competent larvae is done when the rudiment is greater than 320 m in diameter and
the larvae are between 14 and 17 d old. Larvae
are settled on cultured benthic diatoms Navicula
spp. in 100-L tanks of 1 m diameter. A few days
after settlement, cultured red alga Gracilaria
conferta is added to the tanks. Young P. lividus
quickly move onto the algae. About 1 week
later, small amounts of cultured U. lactuca are
added also. Growth to 30-mm test diameter
takes about 2 years.
Canada
Currently, there is one research laboratory at St.
Andrews Biological Station, New Brunswick,
working with larvae and one private sea urchin
189
hatchery in Canada Island—Scallops, Ltd., located in Parksville, British Columbia. The company is entering commercial production. Island
Scallops produced 750,000 small (5 mm) green
sea urchins S. droebachiensis in 2000 for aquaculture production and fishery enhancement and
a smaller number of red sea urchins S. franciscanus. Expected production in 2001 is 3 million
S. droebachiensis and 750,000 S. franciscanus. Island Scallops is also working with S. droebachiensis collected from wild population and conducting gonad enhancement studies (see Nutrition section).
At Island Scallops, larvae are reared in a
static system at four larvae/mL, with single
bubble aeration to maintain larval distribution
in the water column. The size of the rudiment
is used to determine the time of metamorphosis. Larvae are settled on polycarbonate plates
held in racks. Jaw formation occurs in about 4
d. Ambient seawater is used during culture and
ranges between 9°C and 14°C. Large diameter
pipe is cut longitudinally and used as a nursery system (Y. Alabi, Island Scallops, Ltd.,
Qualicum, Canada, personal communication).
The university research group, lead by Dr.
Shawn Robinson, is rearing S. droebachienis for
laboratory research and offshore field trials in
commercial grow-out facilities. The research
group has already completed preliminary gonad maturation studies and juvenile rearing
methods (Morgan 2000; S. Robinson, Department of Fisheries and Oceans, St. Andrews,
Canada, personal communication).
De Jong-Westman et al. (1995a) examined
the effects of adult diet on egg size and number, larval development, survival, and metamorphic success for S. droebachiensis. Adults were
conditioned for 9 months with eight experimental diets: 1) Low protein: (LoPro < 10% protein);
2) High protein: (Hi Pro > 20%); 3) LoPro + M
(with mannitol 9.7%); 4) LoPro + A (with 9.75%
algin); 5) Hi Pro +C (with 0.5% cholesterol); 6)
Hi Pro + b (with 0.006% b -carotene); 7) HiPro C
+ b (with 0.5% cholesterol and 0.006% b -carotene); and 8) Air dried kelp: Nereocystis luetkeana.
Spawn induction during the natural spawning season (March) was conducted using 0.1
M acetylcholine through the peristomal membrane. Diet had no effect on egg size or fertilization rate. Egg energy content was lowest on
LoPro and highest on HiPro with no difference
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in the other diets. Larval culture was completed
for diets 1, 2, 6, 7, and 8. Fertilization did not
differ among the five diet treatments. Larval
development had no pattern, but larvae fed diet
7 formed the eight-arm stage 3 d earlier than
other treatments. Larvae from parents fed diet
8 were abnormal, and developmental stages
could not be determined. Larval survival at the
six-arm stage was 92–95% on diets 1, 2, 6, and 7.
Diet 8 had high mortality with 15% survival on
day 20. Only larvae from diet 6 consistently
showed faster larval development from embryonic stages. Larvae from diets 6 and 7 were also
13–18% larger than those reared by McEdward
(1986) from broodstock fed algae. Overall, this
study showed the diet of the adult may influence the larvae and that larva like adults respond to their environment by changes in shape.
Other larval research in Canada has shown
S. droebachiensis growth is most rapid at 14°C
(Hart and Sheibling 1988); growth can be accurately compared measuring the oral arms
(McEdward 1984); settlement with developed
microbial films induced more settlement than
plates without films (Pearce et al. 1990).
Chile
Chile has a highly regulated aquaculture industry with over 13 species of fishes, algae, and invertebrates commercially cultured. The commercially important sea urchin Loxechinus albus
is cultured on a research and development scale
at government (Instituto Fomento Pesquero at
Huehue and Putemún) and university research
facilities (Universidad Catolico del Norte,
Universidad de Conceptión, Universidad
Andres Bello) and several private hatcheries
(Fundacion Chile, Palo Colorado Cultivos
Costeras, and others) (Norambuena and Lembeye 2003). Of these facilities, government and
private operations produce about 3 million
seed per year but have an estimated total seed
production capacity of 18 million seed (Letelier
2003) (Figure 6).
Loxechinus albus is successfully cultured
using established methods. Adults are induced
to spawn with 0.5 M KCl and reared in a laboratory system to the eight-arm echinoplutei
stage. Metamorphosis was induced with bacterial films. Larvae are fed Dunaliella tertiolecta,
Chateoceros gracilis, Isochrysis galbana, or a mixed
Figure 6. —Juvenile Loxenchinus albus at the Instituto
de Fomento Pesquero hatchery in Huehue, Chile.
diet of both algal species in flow-through systems. Seawater is filtered to 1 m and flow rates
are low; about one-third to two-thirds of the
water is exchanged in 24 h. Larvae fed the mixed
diet completed metamorphosis after 33 d at 10–
12°C and after 20 d at 18–20°C. Larvae were
settled with benthic diatoms, Navicula spp.,
Nitzchia spp., and Cocconeis spp., in 2-L, clear
plastic containers. Young L. albus reach 500–
7,200 µ after 76 d (Gonzales et al. 1987; Bustos
and Olave 2001).
Mass culture of newly settled L. albus is conducted in large rectangular tanks (5.2 × 1.3 ×
0.65 m, 4,400 L) with fiberglass plates inoculated
with pinnate diatoms. When sea urchins reach
5 mm in test diameter, some are moved to suspended long-line and cage systems. Loxechinus
albus reaches commercial size, 50–55 mm, in
about 30 months. Chile has a patented prepared
diet used to feed L. albus during the long growout period (Bustos and Olave 2001).
Mexico
In 1994, the Universidad Autónoma de Baja
California began research and production of
juvenile S. franciscanus and S. purpuratus on an
experimental scale. The program started in response to declining fishery harvests. Approximately 15,000 juveniles are produced each year.
The juvenile sea urchins are used for laboratory research, cage culture grow-out research,
and have been seeded to artificial reefs. The
white sea urchin Lytechinus pictus is cultured for
research on G-proteins and signal transduction mechanisms between the sperm and egg
(E. Carpizo, University of Hawaii, Honolulu,
personal communication).
United States
Some important laboratory studies were completed in relation to embryological studies of
sea urchins in universities. Hinegardner (1969),
who studied several species from the east and
West Coast of North America, comprehensively
described sea urchin larval rearing and metamorphosis (Figure 4). Cameron and Hinegardner (1971) identified key factors that induce
sea urchin larval settlement.
In California, the sea urchin fishery funded
aquaculture research for S. franciscanus at the
University of California Davis Bodega Marine
Laboratory. The sea urchins produced from the
system were used in stock enhancement experiments. Wild, adult broodstock were induced to
spawn with 0.5 M KCl. Eggs were collected in
filtered seawater and sperm was collected in
chilled bowls without seawater. Eggs were fertilized using 1,000 sperm/egg. Fertilized eggs
were placed in 1,500 mL of 5-m filtered seawater. Larvae were cultured at high densities, 5–
7/mL, in a static system using 1,500-mL glass
containers with stir paddles moving at 25–30
rpm (revolutions per minute). Larvae were fed
a single-celled algae Rhodomonas lens at 60–
10,000 cells/mL. Algae were cultured in heat
sterilized (70°C) seawater and PrvaosoliGuillard culture medium (Guillard 1975). Transferred cultures took about 5 d to bloom to high
enough densities for feeding (>500,000 cells/
mL) under grow lights at 22°C. Cultures were
reared in 17-, 23-, and 100-L containers. Cultures
attained peak densities of 1.25 million cells/mL
around day 10 and exhibited a dark red color.
They were used until densities declined,
around day 13.
Larval urchin survival was variable among
spawn cohorts and within each spawn. Bacterial contamination was initially a problem but
was controlled by rinsing larvae onto 10-m
screens and cleaning the jars daily with freshwater. Over time, larval survival averaged 61–
66% at day 16 postfertilization and 32% on day
22, 1 d prior to settlement.
Settlement of larvae varied and occurred
191
over 2 to 3 weeks with high rates of metamorphosis, 60–90%. Newly settled S. franciscanus
were 0.40 mm ± 0.038 (mean ± SD) in test diameter. At settlement, juveniles lacked functional
jaws. When the jaws emerged, diatoms, red turf
algae, and kelp Macrocystis pyrifera were placed
in the settlement tanks. At 6 months of age, the
juveniles averaged 10.0 ± 2.6 mm, at 9 months
16.4 ± 5.4 mm. One year later, approximately
1.7% survived from fertilized embryos. Survival
estimates, calculated from the end of the larval
rearing period (with 32% surviving) was 5.3%.
The laboratory-cultured sea urchins were used
for fishery enhancement experiments (RogersBennett et al. 1994).
In New Hampshire and Maine, cultivation
and growth studies with S. droebachiensis have
been conducted for several years (Harris et al.
2003). Sea urchins are produced for laboratory
research, stock enhancement, and sea ranching.
Adult sea urchins are spawned with standard
spawning and fertilization techniques (Hinegardner 1969; Strathman 1987). Laboratory research with S. droebachiensis testing several algal diets during larval rearing found Nanochloropsis superior to Dunaliella tertiolecta and
Isochrysis galbana. Survival and settlement were
low compared to other studies, but the researchers plan to expand the culture research
(Lake et al. 1998). Juveniles are settled in fiberglass tanks with microalgal films and grown
to approximately 15 mm in test diameter. Numerous experiments indicate outplanting in
winter months is most successful as natural
predators are less active (Harris and Chester
1996).
Water flow in rearing containers is also important for sea urchin gonad growth. Feed ingestion did not vary when S. droebachiensis were
held in 350 mL/min compared to 219 mL/min,
but somatic and gonad growth was greater in
the lower flow rate (Tollini et al. 1997).
Adult Lytechinus variegatus were fed a prepared diet for 10 months (George et al. 2000).
Following spawn induction, egg size, and time
to metamorphosis showed the prepared diet
supported development similar to those from
field populations.
Large-scale culture work with sea urchins
is in the initial stages in several universities in
Canada, the United States, New Zealand, Norway, and Scotland. Undoubtedly, new culture
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systems will emerge as additional sea urchin
species are cultured.
Nutrition
Studies of sea urchin nutrition using natural
and prepared diets and examination of the associated somatic or gonadal growth have been
active areas of research for the past century.
Much of the earlier research resulted from interest in these extraordinary animals, and,
more recently, nutritional research has overlapped with fishery depletions and the market demand for sea urchin products. Somatic
growth and annual gonadal growth patterns
complicate sea urchin nutrition. Somatic
growth is slow after metamorphosis to about
5 mm, rapid juvenile growth to about 15–30
mm, and then slow growth in the adult stage.
The annual reproductive cycle results in seasonal gonadal growth. These patterns suggest
sea urchins may have different nutritional requirements during their life history as well as
seasonal differences.
The normal food of edible sea urchins is
algae, but numerous studies have shown that
they may also act as carnivores or scavengers.
Sea urchins apparently feed continuously if
food is available. Digestibility is generally
high (>80%) for organic matter, protein, energy,
and soluble carbohydrates, but may be low for
lipid and insoluble carbohydrates (about 50%)
(Klinger et al. 1998; Lares 1999). Digestive processes include enzymes and gut bacterial communities that break down dietary components.
Many questions remain regarding the transfer
of nutrients from the digestive system to the
hemal system and gonads. The sea urchin digestive system and gonads respond to food
availability by increasing or decreasing in size.
Sea urchins may utilize nutrient reserves in any
body tissue during starvation or may show
rapid growth with high quality food available.
There is no discrete nutrient storage site or
sites of nutrient reserves in the digestive system, and the conspicuous gonads are believed
to partly serve this function.
Excellent reviews of sea urchin nutrition
for wild populations can be found in Anderson (1966), Lawrence (1975), and Lawrence and
Lane (1982). In this section, a review of juve-
nile and adult sea urchin nutrition studies using both wild and cultured animals is presented.
Gonad Growth and
Enhancement Studies
Algal Diets
The scientific literature on ecological relationships between sea urchins and algae in the natural environment is enormous. Here, I will review only those studies with objectives relevant
to aquaculture.
The European edible sea urchin Paracentrotus lividus was fed 12 macroalgae ad libitum for a 6-month period to examine gonadal
growth. Findings related food ingestion to gonadal growth where P. lividus, which digested
more than 3 g of organic matter per day, showed
gonadal growth. Above this food intake rate, the
species of macroalgae did not have a significant effect on gonadal growth. Absorption rates
were strongly correlated with food preferences.
The algae species included three red, six brown,
and three green algae, all of which were dominant in the natural habitat of the P. lividus collected. The highest gonadal growth was found
on the Rhodophyte species Rissoella verruculosa
and the lowest on the red algae Asparagopsis
armata and the brown algae Dilophus spiralis. Differences in ingestion rates were attributed to
attraction factors and chemical defenses of the
algal species tested (Frantzis and Grémare 1992).
Two interesting studies have examined the
feasibility of out-of-season gonad enhancement
of S. droebachiensis. One study was conducted
in the laboratory and compared to natural
populations (Hagen 1998), and the second study
was conducted in cages held near the shore
(Vadas et al. 2000). Both studies collected S.
droebachiensis from barren ground habitat devoid of macroalgal species during the postspawn or summer season. In the laboratory
study (Hagen 1998), S. droebachiensis were fed
Laminaria hyperborea, L. digitata, L. saccharina, and
Alaria esculenta and attained maximal gonad size
before field populations. This study also examined optimal size for gonad enhancement and
found S. droebachiensis of 50–60 mm in test diameter would provide aquaculturists with
maximal gonad yield for the time and food invested.
Four algal species, A. esculenta, L. digitata,
Palmaria palmata, and Ulva lactuca were fed individually, and a fifth treatment of a mixed diet
that included all algal species was used to examine gonad production to S. droebachiensis in
sea cages (Vadas et al. 2000). The red alga P.
palmata induced the most rapid and greatest
gonadal production and was equivalent to the
mixed diet. Alaria esculenta and L. saccharina produced the lowest yields. The yields after 3
months were significantly greater in the experimental animals (10%) compared to field
samples (4–6%). Both studies suggest out-ofseason gonad enhancement using algal diets is
possible with S. droebachiensis.
Single and multiple algal diets were also
tested with S. droebachiensis in Atlantic Canada
(Hooper et al. 1997). Adult S. droebachiensis of
45–55 mm in diameter were fed one of four diets: 1. Individual species of algae: Agarum
clathratum, Alaria esculenta, Fucus vesiculosus,
Ascophyllum nodusum, Laminaria longicruris, or L.
digitata; 2. L. digitata at 100%, 75%, 50%, 25%, or
0% of satiation; 3. A 50:50 mixture of L. digitata
and L longicruris;or 4. fresh frozen herring.
The algal species Agarum clathratum, Alaria
esculenta, Fucus vesiculosus, and Ascophyllum
nodusum produced little gonad growth and were
unsuitable for commercial quality requirements. Laminaria digitata increased gonad yields
to 10% in 4–6 weeks. Laminaria longicruris produced similar gonad yield over an 8–10-week
period. Gonad yield was not different between
treatments in the ration experiment, suggesting
assimilation was increased in the lower rations.
The mixed diet (3) showed no significant differences in gonad yield compared to either species fed individually. This result provides the
aquaculturist with more choice when planning
an urchin feed lot. The fish diet resulted in unacceptable gonad yield and high mortalities.
Seasonal feeding trials using diet 3 and started
in June, July, August, and September had similar results as those from the first experiment. A
trial started in October had low feed ingestion
rates and low gonad production. There would
appear to be little advantage to winter feed lots
in this northern region.
In western Canada, S. franciscanus were fed
fresh or frozen kelp, Nereocystis luetkeana. The
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fresh kelp was used in a 54-d experiment with
large, 95–110-mm animals and resulted in a
doubling of the gonad index (5.5% to 10.3%)
between September and November. Trials with
frozen kelp were longer, 150 d, and tested three
size-classes of S. franciscanus, 15–26 mm, 47–56
mm, and 70–110 mm, between October and April.
For this experiment, laboratory results were compared to the field population where the urchins
were collected. Gonad indices increased from
0.04% to 12.4%, 4.2–12.4%, and 6.5–22.1% for
small, medium, and large S. franciscanus, respectively. Gonad indices for field populations were
much lower: 0.01%, 0.8%, and 5.5% for small,
medium, and large urchins, respectively. Costs
of freezing large amounts of kelp (150 kg in this
study) need to be analyzed for economic feasibility, but it appears gonad enhancement of this
species is feasible (Bureau et al. 1997).
Also on the West Coast of North America,
S. purpuratus were held in nearshore cages and
fed Macrocystis pyrifera (Hudson 1991). This
study tested the feasibility of developing a commercial product from S. purpuratus collected
from food-limited barren areas. When removed
from the sea cages, 30- and 45-kg samples were
commercially processed. Gonad weight increased at rates greater than 1% per week over
10-week trials. The improvement in yield and
quality were confirmed when the samples were
sold in Japan as grade A ($17.00/lb) and grade
B ($7.50/lb), both 1991 prices. This trial was later
expanded to a commercial operation on a 31.16
acre offshore lease, which successfully fattened
S. purpuratus until a large winter storm destroyed the long-line system in 1998 (J. Hudson,
commercial sea urchin fisherman, Santa Barbara,
California, personal communication).
In Scotland, polyculture of Psammechinus
miliaris with Atlantic salmon Salmo salar net-pen
systems was examined by rearing the urchins
(11–16 mm diameter) in lantern or pearl nets.
The lantern nets were placed in salmon cages
and under walkways connecting the cages. Lantern net mesh was large enough to allow salmon
pellets to enter, and pearl net mesh was not. A
control group of sea urchins was fed Laminaria
saccharina. P. miliaris in the lantern nets had significantly greater somatic growth and gonad
indices than animals in the pearl nets (19.08%
vs. 10.35%). This result suggests it is advantageous to locate the urchin net culture systems
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where they have access to uneaten salmon pellets (Kelly et al. 1998).
The Japanese red sea urchin Pseudocentrotus
depressus from two cultured populations were
fed the brown algae Eisenia bicyclis for 1 year.
Field samples were compared to the laboratory
animals, in which monthly subsamples measured somatic growth, gonad index, and histological analysis (Unuma et al. 1996). Laboratory
populations maintained a higher gonad index
over the year with significantly less decrease
following spawning than field populations (5%
vs. 2%). The laboratory group did not increase
in gonad index as rapidly as the field population; however, gametogenesis was delayed
about 2 months and was sustained longer. The
authors suggest environmental factors in the
laboratory study are probably responsible for
the differences between the two populations.
From an aquaculture perspective, the sustained
mature condition of the gonads should be
avoided. Shortening the mature period by controlling the environment or changes in the feed
may provide methods to maintain the immature gonadal condition (Unuma et al. 1996).
Overall, algal diets successfully enhance sea
urchin gonadal growth. The main concerns are
the costs of natural algae, availability of algae,
and possible negative impacts to the natural
environment. Comparison of algal and prepared diets was a natural follow up to testing
algal diets, and several studies have done this.
Comparison of Algal and Prepared Diets
Several published studies have compared gonadal growth for sea urchins fed natural algal
diets and prepared diets. Seven prepared diets
and air-dried Nereocystis luetkeana were fed to
adult S. droebachiensis (50–70 mm) collected from
a population near Vancouver Island. The composition of the diets is the same as those shown
in the “Development of Aquaculture” (de JongWestman et al. 1995a) section. The experiment
was conducted from July 1991 to March 1992
with subsamples taken from each treatment
every 6 weeks. All of the HiPro diets and N.
luetkeana had higher gonad indices than S.
droebachiensis fed the LoPro diets. It is important to note that gonad indices were calculated
as wet gonad mass/drained test mass × 100.
Initial gonad indices were 15.9–17.8% and final
gonad indices were 32% and 39% for LoPro
and HiPro, respectively. There were no significant effects of diet on somatic growth, gonad
lipid, or dry matter content.
Adult S. droebachiensis (40–60 mm) were collected by scuba diving and sorted into 15
groups. Three agar-based diets were compared
to Laminaria longicruris in cages suspended from
a long-line system. The sea urchins were fed
approximately 10 kg every 2 weeks over a 3month period. Gonad production was greatest
on a prepared diet containing carrots, cabbage,
soy meal, potato starch, seawater, and guar gum
as a binder (Diet A). The other two diets contained the same ingredients with poultry meal
substituted for soy meal (Diet B) or raw potato
instead of raw cabbage (Diet C). The initial
sample and samples from the wild population
had gonad indices of 4.3–4.9% at the beginning
and end of the experiment. The prepared diets
showed final gonad indices of 9.8% and 8.0%
for prepared diets A and B and 7.5% for prepared diet C and L. longicruris. Similar to other
studies, the prepared diets showed greater gonad production than macroalgae but suggest
that refinement of prepared diets for improved
gonad production is essential for successful sea
urchin aquaculture (Robinson and Colborne
1997).
Between 1991 and 1994, several 4- to 5-week
studies were completed with S. droebachiensis
fed semimoist prepared diets or dried Laminaria
longicrispus. Diets were formulated with algae,
wheat gluten, starch, calcium phosphate, calcium carbonate, calcium sulfate, vitamins, choline chloride, and vitamin C into rubbery, sinking pellets. Sea urchins were collected by divers
and experiments conducted in laboratory tanks
at densities of 40–50 g/L of seawater. Conditioning in January was inconclusive with seawater temperatures below 6°C. Gonad indices
between 11% and 12% from initial values of 3.4–
6.4% were found in May, July, August, and October trials for prepared and algal diets. These
studies again showed it is possible to increase
the gonad index in a relatively brief period
(Motnikar et al. 1997).
Cultured Loxechinus albus were maintained
in cages on a long-line system and in laboratory aquaria. Four diets were tested: two extruded feeds, one with and one without kelp,
and Macrocystis pyrifera and Ulva lactuca. The
experiment was conducted for two 4-month
periods, one during the summer (December to
March) and one during the spring (August to
November). Whole live weight was 72 g at the
start of both experiments. Gonad index was significantly greater for L. albus fed the prepared
diet in the spring for both culture systems compared to the algae diets (19% vs. 8%) and had
significantly increased from the initial sample.
In the summer, gonad index results showed the
same pattern, but gonadal growth was greater.
Sea urchins fed the prepared diet increased from
5.5% to 20% compared to a gonad index of 11.7%
found in the algal diet treatments (Lawrence et
al. 1997). This study confirmed that for some
species, gonad production is greater with prepared diets than algal diets or fishery yields.
Large S. franciscanus collected from a natural population off northern California had an
initial gonad index of 3.4% and weighed 248 g.
Sea urchins were fed the prepared diet with kelp
(as for L. albus, Lawrence et al. 1997) or fresh
Nereocystis luetkeana from June to November at
two seawater temperatures, 12.9°C and 16.1°C.
Final gonad production was not significantly
different between treatments and was 19.2%
(McBride et al. 1997). For this species, it appears
high gonad indices are possible from both algal and prepared diets.
A very comprehensive study with three sizes
of Evechinus chloroticus examined four prepared
diets and a combination algal diet of Macrocystis
pyrifera and Ulva lactuca. This study was conducted during three stages of the reproductive
season, postspawning (February to May), gonadal growth (June to September), and late gametogenesis (October to December). The three
size-classes were small (30–40 mm), medium
(50–60 mm), and large (70–80 mm). All comparisons included an initial and final sample from
the natural population. Field samples from the
small size-class did not develop gonads. Gonad
indices from small and medium urchins were
generally similar in the postspawning and late
gametogenic stages, and the prepared diets supported greater gonadal growth than algae. Between June and September, there were no significant differences in gonad indices between the
prepared and algal diet for small and medium
E. chloroticus, but they were all greater than the
field samples. Large E. chloroticus gonad indices
were greater in the prepared diets than algae but
195
not the field samples in the postspawn season.
During gonad growth and late gametogenesis,
large E. chloroticus gonad indices were larger for
urchins fed the prepared diets compared to algal diet treatments and the field samples (Barker
et al. 1998).
In Scotland, polyculture of Psammechinus
miliaris and Atlantic salmon showed some interesting results. The sea urchins efficiently utilized
a prepared salmon diet rich in protein and lipid
resulting in acceptable somatic and gonadal
growth. In another study, gonadal production
was greatest for P. miliaris-fed salmon feed (20–
57%) compared to natural algal diets (2–12%) over
a 12-month period (Cook et al. 1998). The gonad
indices of monthly subsamples showed a large
gonad mass with negligible decline after spawning and an extended spawning period for urchins
fed the prepared diet treatment. The sea urchins
fed an algal diet, Laminaria saccharina, had a
spawning period of 8 weeks with substantial
declines in gonad mass, lipid, and protein content. The elevated gonad production results suggest a more refined diet could result in successful aquaculture for this valuable species. The
pattern of extended spawn season and no large
changes in gonad index during the annual reproductive cycle is validated in studies with
other prepared diets.
Prepared Diet Only
The suggestion to develop prepared diets for
sea urchin nutrition research (Lawrence 1975)
has been a stimulus for many studies. Agarbased research diets and extruded pellets have
been developed and tested with many sea urchin species. So far, most of these studies have
been on nutrition using wild sea urchins, not
cultured ones. This situation is changing rapidly as many research laboratories are developing mass culture techniques.
The first published study using a prepared
diet was Nagai and Kaneko (1975). Strongylocentrotus pulcherrimus was fed a prepared diet
to examine feed ingestion and assimilation efficiencies. The prepared diet contained 23.3%
each of fish, soy, corn, yeast, and 0.1% vitamins
and was bound by cooking with agar. Mortalities were dissected and found to have a gonad
index of 20–25%.
Since Nagai and Kaneko’s study, sea urchin
196
MCBRIDE
prepared diets have been used in Japan (Hagen
1996). The preferred food for cultured sea urchins is kelp, but prepared pellets are used
when algae are not available.
Gonad production of small (5 g) and large
(60 g) Paracentrotus lividus was examined using
agar-based diets that were similar except for the
protein source. One diet utilized fish and the
other soybean. Groups of each size-class of P.
lividus were fed the diets either continuously or
every 3–4 d. Gonad index increased from 0.5%
to 4.4% and was similar in both feed regimes
for small P. lividus. Gonad index for large P.
lividus increased from 0.8% to 5.5% and was not
significantly different between diets or feed
schedules. These results suggest the protein
available from both fish and soy is suitable for
gonad enhancement (Lawrence et al. 1989).
In a large and complex study, small cultured and large wild P. lividus were fed three
prepared diets or an algal diet Cymodocea nodosa
in laboratory tanks with recirculating seawater
or fresh incoming seawater. The diets contained
fish, vegetable or mixed protein sources. Temperature was controlled at 18–20°C or maintained at ambient seawater temperature. Tanks
were either in total darkness or natural photoperiod. Mixed diets, fresh seawater, and natural temperatures resulted in higher gonad indices for all size-classes and ranged from 11% to
15%. These values were higher than natural
populations or P. lividus fed C. nodosa. In the recirculating system, final gonad indices were 5–
7% in all treatments. Interactions between dietrecirculation versus continuous flow and size
shows that a mid-size-class, 20–25 mm diameter P. lividus had the highest gonad indices.
Gonad index results can be grouped into three
categories: 1. sea urchins fed C. nodosa, 2. all
diets and light conditions at the controlled temperature and 3. all diets and light treatments
with flowing seawater. Groups 1 and 2 had
similar gonad indices and group 3 had the
higher value (Fernandez and Pergent 1998).
Three papers have tested extruded pellet
diets developed by Dr. John M. Lawrence (Department of Biology, University of South
Florida) and Dr. Addison L. Lawrence (Texas
A & M Shrimp Mariculture Project) and manufactured by Wenger International, Inc. (Kansas
City, Missouri). The pellets are approved by
the U.S. Food and Drug Administration and the
U.S. Department of Agriculture. In the following section, these diets are referred to as the
pellet diet.
Adult S. droebachiensis (50.4 ± 3.9 mm, 47 ±
2 g) were fed the pellet diet during two seasons, prior to the annual spawning (8-week experiment) and after spawning (12 week). Two
pellet diets were used: one with fish meal as
the protein source, and a second using soy
were fed ad libitum. Sea urchins were collected
from natural populations and the experiment
was conducted in a recirculation system at 34
parts per thousand, 6–8°C, and 12/12 photoperiod. In the winter prespawn study, initial
gonad index was 17.1% and increased slightly
to 19.7% in both diet treatments. In the summer post-spawn study, initial gonad index was
4.9% and increased to 20%, comparable to
maximum gonad production for this species
from natural populations. Both feeds were sufficient to support gonad growth (Klinger et al.
1998).
The same diet was tested with S. droebachiensis
collected by diving and placed in ambient photoperiod or a photoperiod set four months ahead
using artificial lights. The experiment began in
March and the altered photoperiod treatment set
for July sunrise and sunset was a 4-month photoperiod advance. A subsample from each tank was
taken monthly. All subsamples resulted in gonad
indices around 20%, significantly higher than
those taken from concurrent field samples. Results
of the reproductive condition of these sea urchins
will be presented in the Reproduction section
(Walker and Lesser 1998).
A ration study with a soy-based pellet was
tested with wild S. franciscanus. Adult S.
franciscanus, 91 mm, 295 g, were fed 1 g/d, 3
g/d, or not fed. Initial gonad index was 3.3%
and increased to 7.1% and 12% in the low and
high rations, respectively. There was no change
in the gonad index of unfed urchins. The experiment lasted 60 d. The results show S.
franciscanus can also be fed pellet diets and that
gonadal production may be controlled by food
ration (McBride et al. 1999).
In the recirculation system described by
Grosjean et al. (1998), Paracentrotus lividus were
fed a pellet diet for 1 month (30 d). In each 48 h
period, diets were fed ad libitum for 8, 16, 24,
32, 40, or 48 h. Paracentrotus lividus with food
available for 35 h or more had the highest go-
nad production. These results suggest P. lividus
does not feed continually to produce large gonads and that the quantity of food can be estimated to prevent waste (Spirlet et al. 1998).
Agar-based diets have also been used to test
effects of protein on gonad enhancement. Diets
with 30%, 40%, or 50% protein were fed to small
S. franciscanus for 10 months. Initially, the sea
urchins were immature and had very small gonads. This range of diet protein content was relatively high and did not impact gonad production. Gonad index increased equally in all diet
treatments to 16% (McBride et al. 1998). Gonad
index was not significantly different for S.
droebachiensis-fed agar based diets with protein
concentration ranging from 19% to 29% (Pearce
et al. 2002).
Adult Lytechinus variegatus (37–64 mm, 30–
110 g) were fed one of two prepared diets for 10
weeks. Diet 1 was a pellet diet from Wenger
International, Inc. Diet 2 was agar-based and
similar to a catfish diet. Both diets resulted in
equally large gonad production (Watts et al.
1998).
As can be seen from studies with algal or
prepared diets, sea urchin gonad enhancement
is quite readily achieved. Laboratory and inwater studies feeding sea urchins algal or prepared diets have shown an average increase
gonad size of about 1% per week. The difficult
part is controlling the quality of the gonads.
Often when sea urchins are fed in a controlled
environment, the gonad becomes soft or an undesirable color. Researchers are now examining additional quality aspects that can be improved or manipulated by diet. Among the important factors under consideration are color
and reproductive stage.
Gonad Color
Color is among the most important appearance
factors in sea urchin roe products and was recognized as an early challenge to sea urchin
aquaculture (Matsui 1968). Prepared diets tend
to give a light tan or pale gonad color. This has
been noted by nearly every study mentioned
above in the nutrition section. Algal diets tend
to give excellent color unless the urchins are
collected from an extremely food limited environment where the gonads tend to be very dark,
197
almost black or brown. In some species, this
dark color persists after feeding for 2 to 3
months. Research on pigments that influence
gonad color has not been successful (Motnikar
et al. 1997), as the pigments tested have generally had no influence on gonad color. An innovative method to investigate the efficiency of
transfer of pigment from prepared diets to gonads, used reflected light fiber optic spectrophotometer using CIE (Commission Internationale de l’Eclairage) L * a * b * units of measurement (Robinson et al. 2002). This method
improves on previous approaches of determining gonad color by comparison with color
swatches. Distinct pigment sources can be qualitatively and definitively measured using the
CIE system. Robinson et al. (2002) found a natural source of b-carotene from dry Duneliella salina
produced the most acceptable color in S.
droebachiensis.
Feed Ingestion Rates
Reports of sea urchin feed ingestion rates are
given in most of the studies presented in the
Nutrition section and are summarized in Table
3. Trends seen include the inverse relationship
of protein content and feed ingestion. A word of
caution, most sea urchin studies cited here do
not consider energy content of the diets. Since
energy is the first limiting factor in biological
systems, the feed ingestion rates presented
should be considered with this in mind.
Control of Reproduction
Many elegant studies have described the annual reproductive cycle of a wide variety of
edible and other species of sea urchins. In general, edible sea urchins reach sexual maturity
at about 1–2 years of age and 25–30 mm in test
diameter or when they reach approximately
30% of their adult size (Pearse and Cameron
1991; Lawrence 1982; Walker et al. 2001). However, sustainable sea urchin aquaculture requires maintenance of breeding populations
in addition to understanding the natural reproductive cycle. The development of sea urchin
aquaculture has been primarily focused on
gonad production. Regulation of gonadal
growth and gamete development has been
n.d.
51 mm, 63 g
37–64 mm
47 mm, 50 g
L. variegatus
L. variegatus
S. droebachiensis
37
4.4 g
4.4 g
60 g
n.d.
49
41.7
49
36
40 (fish + soy) 32
40 (soy)
32
23
64
40
31
23
64
37
12.4
36
49
5.1
5.1
1
7
2
0.5
n.d
0.5
5
0.5
25–54 1–4
5–10
37
64
7
lipid
20
carb.
17
17
n.d.
n.d.
9
n.d.
21.3
n.d.
n.d.
n.d.
20–40
9
ash
Diet composition (% dry matter)
protein
30 mm
50–60 mm
70–80 mm
30–40 mm
50–60 mm
70–80 mm
30–40 mm
50–60 mm
70–80 mm
30–40 mm
Size
Lytechinus
variegatus
P. lividus
Strongylocentrotus
pulcherrimus
Paracentrotus
lividus
Evechinus
chloroticus
Species
pellet without kelp
agar
agar
agar
agar
pellet
agar
pellet with
kelp meal
Risoella
verruculosa
agar
agar
agar
Macrocystis
pyrifera
pellet
Food type
0.05
0.08
0.31
0.34
0.44
0.47
0.18
0.44
0.14
0.63
postspawn
prespawn
postspawn
0.4
0.05
0.05
0.10
0.10
0.1–0.14
0.1–0.2
0.1–0.24
0.05–0.06
0.04–0.12
0.04–0.18
0.09–0.12
0.09–0.4
0.16–0.54
Food ingested
ad lib., 16° C
ad lib., 23° C
ad lib.
ad lib.
ad lib.
ad lib.
prespawn
ad libitum
ab lib.
every 3–4 d
every 2–3 d
ad lib.
ad lib.
ad lib.
Food offered
Klinger et al. 1997
Watts et al. 1998
Klinger et al. 1994
Klinger et al. 1986
Frantis and Grémare 1992
Lawrence et al. 1991
Nagai and Kaneko 1975
Barker et al. 1998
Study
Table 3.—Diet composition and feeding rates of sea urchins fed natural or prepared diets (pellet = extruded diet, agar = agar-based research diet, no data =
n.d., carbohydrate = carb, ad libitum = ad lib.). Algal diets are given as genus and species. Food ingested is given as dry feed ingested/animal/d. Size is given
as test diameter (mm) or whole animal weight (g).
198
MCBRIDE
Size
S. franciscanus
S. franciscanus
30
40
50
91 mm, 295 g 20
35 mm, 20 g
23
S. franciscanus
lipid
n.d.
6.9
1.4
3.1
ash
n.d.
n.d.
n.d.
n.d.
42.2
30.7
20.2
64
14
7.0
7.0
7.0
0.05
0.05
8.4
8.7
9.0
8.8
2.5
0.5–1.5
0.6–1.8
1.0–2.5
1.0–4.0
23–54 1.4–4.4 27–49
n.d.
n.d.
n.d.
25 mm, 8.6 g
33 mm, 19.7 g
40 mm, 37.8 g
54 mm, 76.8 g
90 mm, 248 g 2.5–4.9
7.4
25.5
15 mm, 2 g
43.9
22.1
carb.
35.6
23.3
protein
Diet composition (% dry matter)
S. nudus
Tripnuestes gratilla 16 mm, 2 g
Species
Table 3.—Continued.
Food type
agar
agar
agar
pellet
pellet
Nereocystis
luetkeana
Ulva
pertusa
Gloio
peltis furcata
Undaria
pinnatifida
mixed algae
Laminaria
religiosa
ad.lib.,
ad lib.,
ad.lib.,
ad lib.,
ad lib.
ad lib.
ad lib.
1 g/d
3 g/d
ad lib.
ad lib.
ad lib.
ad lib.
ad lib.
12°C
16°C
12°C
16°C
Food offered
2.75
4.0
0.99
1.31
1.42
1.25
0.89
0.55
1.42
0.5–1.0
0.07
0.08
0.05
0.06
Food ingested
McBride et al. 1999
McBride et al. 1998
McBride et al. 1997
Agatsuma et al. 1993
Floreto et al. 1996
Study
199
200
MCBRIDE
studied for several sea urchin species. In studies that have focused on reproduction, diet,
temperature, and photoperiod have been investigated.
The recirculating system developed and
used in France has resulted in a successful
breeding method (Grosjean et al. 1998). Broodstock has also been maintained in laboratory
populations by holding the animals in darkness with controlled temperature (Leahy et al.
1978). Both of these systems feed the adult sea
urchins ad libitum, either kelp or prepared
diet. Both algal diets and prepared diets have
been shown to produce healthy viable larvae
(de Jong-Westman et al. 1995a; George et al.
2000) when adults were held in ambient light.
Size at sexual maturity is an important
component of reproduction. Well-fed, laboratory-reared sea urchins can have huge gonads
year round and may also develop gonads at a
very small size. S. purpuratus were full of gametes by 6 months of age when they were only
10 mm in test diameter (Pearse et al. 1986) compared to wild populations where gonads were
not found until S. purpuratus versus 25–40 mm
(Gonor 1972).
The effect of diet on sea urchin reproduction is mostly seen in the size of the gonads and
does not effect gametogenesis. Sea urchins produce large gonads when a preferred food is
available, which results in high food ingestion.
In wild and laboratory populations, high feeding rates often result in extended gametogenesis and spawning activity. Reproductive development is often inversely related to somatic
growth in wild populations (Fuji 1967; Gonor
1972; Pearse et al. 1986) and in laboratory studies (Unuma et al. 1996; Cook et al. 1998; Klinger
et al. 1998). In poor food conditions, natural
populations tend to allocate more resources to
reproduction than somatic growth (Thompson
1982). Laboratory ration studies with sea urchins have resulted in lower gonadal indices
but similar reproductive development (McBride
et al. 1999). When starved, sea urchins can decrease in overall size and in gonad size
(Lawrence and Lane 1982; Levitan 1988).
Diet does not appear to influence gametogenesis except to possibly extend the mature
stage. Gonadal changes during the reproductive cycle result in reorganization of nutrient
stores in the body wall and gonad. Nutrient
stores are generally depleted during gametogenesis and after spawning (Giese 1966; Holland and Holland 1969; Fernandez 1998).
Seasonally, changes of seawater temperature are also often suggested to be responsible
for annual reproductive cycles. However, there
is little relationship between temperature and
spawning season for many species. In areas
with little or no changes in seasonal temperatures, such as the Antarctic or deep sea, annual
reproductive cycles are found in sea urchins.
Both field and laboratory studies show seawater temperature had little effect on gametogenesis of S. purpuratus (Pearse et al. 1986; BaySchmidt and Pearse 1987).
Seawater temperature may initiate gametogenesis out of season, such as in the laboratory
systems of Grosjean et al. (1998) and Leahy et al.
(1978) and in areas where seawater temperatures
have strong seasonal variation. Also, gametogenesis has been induced using temperature for
Anthocidaris crassispina, Hemicentrotus pulcherrimus, and Pseudocentrotus depressus (Yamamoto
et al. 1988; Sakairi et al. 1989).
Photoperiodic control of annual reproductive cycles in sea urchins was first suggested
by Giese et al. (1958). These observations were
confirmed for S. purpuratus in an 18-month laboratory study (Pearse et al. 1986). For this species, when animals were held in a photoperiod
regime 6 months out of phase with laboratory
and field samples held at ambient photoperiod, S. purpuratus developed a gametogenic
cycle 6 months out of phase. Individual S.
purpuratus that were moved between photoperiod regimes so that they experienced less than
12 h of daylight for 12 months had continuous
gametogenesis. These results suggested either
short days stimulated gametogenesis or long
days inhibited it. Confirmation of gametogenic stimulation from short days was shown by
Bay-Schmith and Pearse (1987).
Commercially important, edible sea urchins appear to vary in response to photoperiod manipulations. Applications of this concept to aquaculture include timing of product
available for markets and sustaining breeding
populations. In a study with S. droebachiensis,
groups of mature adults were held at ambient
photoperiod, in a 4-month advanced photoperiod, and fed an extruded pellet diet. Only males
showed gametogenesis stimulated by the ad-
vanced photoperiod. The ambient seawater temperatures used in these studies did not influence gametogenesis (Walker and Lesser 1998).
In another study with S. droebachiensis,
adults were held in total darkness or all light
for 8 months and fed L. digitata and L. hyperborea. The natural population was used as the
control group. The number of mature males in
the dark treatment was significantly greater
than the controls, but the reproductive condition of S. droebachiensis held in the light treatment was not significantly different than the
controls (Hagen 1997). It appears that males of
S. droebachiensis have been more sensitive to the
photoperiod manipulations examined so far.
Diseases and Parasites
Sea urchins are known hosts of over 100 pathogens and parasites (Jangoux 1987a, 1987b,
1987c, 1987d). Diseases caused by microorganisms are usually bacteria or fungi. Sporozoans
are the most common cause of protistan diseases. Lesions of the body wall associated with
bacteria and mass mortalities of natural populations have been reported (Pearse et al. 1977;
Pearse and Hines 1979). Injury or other stress
is necessary for the formation of body wall lesions (Gilles and Pearse 1986). Symbiotic turbellarians have been reported in echinoids and
occur in the gut and coelm. Sea urchins act as
secondary hosts for trematodes, serving mainly
as a vector and are passed to fish predators.
During culture of sea urchin larvae, bacterial contamination may occur. Larvae become less robust or may die entirely and larval arms regress. Bacterial diseases also infect juvenile sea urchins in Japanese culture
systems (Tajima and Lawrence 2001). Mass
mortalities occur in summer when seawater
temperatures were greater than 20C°. Symptoms include black or green spots on body
surfaces, partial spine loss, and discoloration
of the peristomium. The spring bacterial disease occurs when seawater temperatures are
between 11° C and 13°C.
Disease will be an important consideration
in sea urchin aquaculture as the experiences
with bacteria diseases in juvenile S. intermedius
in Japan may be found with adults in grow-out
systems also.
201
Processing and Marketing
Prior to 1985, a substantial amount of sea urchin roe was salted, steamed, baked, or frozen
for Japanese markets. The product is now sold
primarily fresh. Sea urchins are stored in large
refrigerated rooms near 0°F for up to 3 d before
processing, if necessary. Longer storage is
avoided because it causes the gonads to get soft
and dark.
Processing consists of several steps. The
test is split open and the roe is removed with a
spoon and placed in plastic strainers. The viscera and other extraneous material is carefully
removed from the gonads. For fresh uni, the
plastic containers are placed in large tanks of
1 m by 3 m containing chilled seawater or brine
and a solution of anhydrous potassium alum,
KAl (SO4)2, until the roe becomes firm. Concentration of alum vary between 0.4% and 0.7% and
soak times vary between 15 min and 1 h. The
roe is then drained, placed on absorbent material, and stored in a clean refrigerated room until
final cleaning and packing. Final cleaning is
done with tweezers or small forks to remove
attached membranes. Roe is packed in 150- or
250-g wooden boxes or bulk packs in larger
styrofoam trays. Boxes and trays are packaged
with gonads of the same size and color together.
Whole, firm roe is placed on the top layer. The
packaging process is critical. Workers who
package the gonads into boxes are the highest
paid in the plant and have a good eye for color
and excellent manual dexterity. The best quality roe is kept for the fresh market and highest
prices. Broken gonads, off color, large or soft
roe are used for secondary products. Bulkpacked roe is usually made into other products
such as salted, steamed, baked, preformed, or
frozen roe. After packaging, the boxes or trays
are placed into insulated cartons that fit into
foam boxes. Artificial coolant is added, the cartons sealed and air freighted to Japan. Sanitation is critical for the fresh roe product. Ultraviolet treated water and good refrigeration
maintains a clean environment. Labor costs are
rather high as all the work is done by hand
(Kramer and Nordin 1979; Kato and Schroeter
1985).
The primary market for sea urchin roe is
Japan, where an auction system determines
price daily. Color is extremely important for
202
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marketing. Up to eight grades of roe are used
by processors, and all dark or discolored roe is
discarded. Texture and firmness are also critical marketing factors. Once the roe arrives in
Japan, it is auctioned at the Tsukiji Market in
Tokyo. The prices depend on supply and demand. Domestic roe always brings the highest
price, but during winter months when domestic roe is not available, imported products fill
the demand and may receive high prices.
Because sea urchin gonad products are relatively expensive, many factors influence the
price. Among them are supply and demand factors such as Japanese domestic supply, total import supply, quality of imported roe, demand in
various markets, seasonal demand cycles, competition with other foods, and the exchange rate.
Lower grade product may become more popular as more people eat in fast food sushi shops
where preformed sushi is sold, rather than in
expensive sushi bars where it is made to order.
The amount of imported urchin roe continues to increase as the Japanese economy declines (Sonu 1995; Jones 1998). Sales of Japanese
roe declined and so did that of imports, but the
declines were due to decreased supply of urchins. However, lower price and take-away
sushi shops are more popular in Japan today.
This low-end market increased dramatically in
response to economic recession in Japan over
the past 10 years or so. The Japanese public accepts the 100-g plastic cups that originated in
Maine. This new packaging style has now
spread to other nontraditional exporting countries such as Norway, Peru, and Chile. This product targets supermarket chains and less expensive restaurants.
With the steady demand for sea urchin
products in Japan, Europe, and North and South
America, interest in sea urchin aquaculture is
growing worldwide. Although there are few
commercial operations at present, the experimental projects investigating gonad enhancement will probably lead to fully integrated culture operations.
A preliminary economic feasibility study
in Canada examined costs, stocking density,
mortality rate, feeding, and operating costs for
a land-based or in-water gonad enhancement
business (Burke 1997). Premium quality and
high gonad yield are required for success in
such an endeavor. Knowledge of market factors
and sea urchin biology are necessary to develop
large scale enhancement operations.
In Chile, hatchery construction and equipment were estimated at $106,000 for larval rearing and $7,000 for land-based grow-out tanks
to rear sea urchins 15 mm in test diameter. Annual costs were estimated at $23,000 for salaries, $33,000 for fixed costs, and $9,100 for energy. If 15-mm juvenile Loxechinus albus are sold
for $0.29, the operation would be profitable. If
the young sea urchins were sold at $0.24, there
would be no profit. This estimate requires two
batches of 5-mm juveniles each year. Grow out
to 55 mm taking approximately 30 months is
estimated to cost $404,000 (Gonzales 2003).
The Future
Worldwide demand for edible seafood products, including sea urchin roe, is expected to
continue increasing. Total world fishery harvests of edible products have stabilized around
70 mt since 1995. Sea urchin fishery harvests
will probably remain around 100,000 mt per
year or decline (Andrew et al. 2002). Fishery
resource conditions fluctuate year to year due
to oceanographic events such as El Niño, food
availability, and natural recruitment. There are
opportunities for sea urchin aquaculture under these conditions but development requires
several key pieces of information.
Suitable diets for somatic and gonadal
growth and appropriate feeding regimes with
high feed efficiencies will be needed for gonadal
and somatic growth through the culture period
and to avoid environmental degradation. Complete feed programs addressing nutrition, physical characteristics of the feed, and feed management will be essential for successful sea urchin
aquaculture (Lawrence and Lawrence 2004). Production scale culture systems that include effective broodstock maturation methods will reduce
reliance on natural populations and must be
perfected. Aspects of sea urchin biology that have
not been considered for aquaculture are behavioral considerations such as density, feed management, and growth interactions for these gregarious animals. New product development in
response to changing consumer lifestyle and preferences will make the industry more economically effective and profitable.
Evaluating the costs to develop a sea urchin aquaculture industry in a number of countries must be analyzed given current and expected markets. Appropriate sea urchin species
to culture should be given serious consideration. Most studies have been on species currently harvested in fisheries. These may not be
the best species for aquaculture (Lawrence
1998). Relatively reliable methods to culture
tens of thousands of sea urchins to juvenile size
are well established. However, grow-out methods are not well described.
Development of sea urchin aquaculture
will also rely on positive interactions of the commercial fisheries and aquaculturists. Fishery
harvesters may participate in aquaculture of sea
urchins by supplying broodstock animals for
enhancement programs. Aquaculture of sea urchins would have many benefits relative to
quality requirements for sea urchin products,
as quality control will be easier to manage. And
given the increasing demand for the expensive
sea urchin products, successful aquaculture
ventures are likely to develop in many countries.
Strong aquaculture research programs currently exist in many countries. It will be the responsibility of scientists, fishermen, students
and other sea urchin enthusiasts to utilize these
funds effectively with the objective of developing a profitable and environmentally sound sea
urchin aquaculture industry.
Acknowledgments
This chapter was supported by the National
Sea Grant College Program of the U.S. Department of Commerce’s National Oceanic and
Atmospheric Administration under NOAA
Grant #NA06RG0142, Project Number A/EA-1
through the California Sea Grant College Program. The views expressed herein do not necessarily reflect the views of any of those organizations.
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Sea Urchin Aquaculture - the National Sea Grant Library

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