Newly recorded Karlodinium veneficum dinoflagellate blooms in

Deep-Sea Research II 101 (2014) 237–243
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Deep-Sea Research II
journal homepage: www.elsevier.com/locate/dsr2
Newly recorded Karlodinium veneficum dinoflagellate blooms in
stratified water of the East China Sea
Xinfeng Dai a, Douding Lu a,n, Weibing Guan a, Hongxia Wang a, Piaoxia He a, Ping Xia a,
Huajie Yang b
a
b
State Key Laboratory of Satellite Ocean Environment Dynamics, The Second Institute of Oceanography, SOA, Hangzhou 310012, China
Zhejiang University, Hangzhou 310012, China
a r t i c l e i n f o
abstract
Available online 21 January 2013
Karlodinium veneficum is a cosmopolitan species, but has been poorly recorded in the East China Sea
(ECS) due to its small size and difficulty in identification. The bloom dynamics of this species is not well
understood globally. In this study, we examined its morphological characteristics that suggest the
K. veneficum is the co-occurring bloom causative species of large scale Prorocentrum donghaiense blooms
in spring 2011. The epicone of K. veneficum recorded in the investigated area is conical or rounded, and
the hypocone is hemispherically rounded. The ventral pore is located at the left side of the apical
groove. Nucleus is positioned centrally within the hypocone. Four large irregular chloroplasts are
equally distributed in the epicone and hypocone. The mean length of cultured cells was 13.6 71.2 mm
(range 11.0–15.8 mm) and the mean width was 10.0 7 1.1 mm (range 8.0–12 mm) (n ¼ 50). Cell
abundance of K. veneficum population was low, in the region 1000–1600 cells L 1, along a transect in
the East China Sea on April 19, 2011, when the water column was not distinctly stratified. Cell densities
reached 3 107 cells L 1 along the same transect on May 13 2011 when the bloom occurred in the
10 m layer surface and the water column was distinctly stratified. Cell abundances therefore appear
closely related to water column stratification.
Crown Copyright & 2013 Published by Elsevier Ltd. All rights reserved.
Keywords:
Harmful algal blooms
Karlodinium veneficum
Population dynamics
Upwelling
Water column stratification
1. Introduction
Increasing harmful algal blooms (HABs) in coastal areas have
resulted in ecosystem damage and human health impacts worldwide (Anderson et al., 2008; Heisler et al., 2008). Such problems
are often related to two types of HAB: high-biomass producers
and toxin producers (Geohab, 2001). Several toxic blooms have
recently ocurred in the East China Sea (ECS). Gymnodinium
catenatum and Karenia mikimotoi blooms have been recorded
(Zhou et al., 2008a; unpublished data from the State Oceanic
Administration People’s Republic of China), as well as large-scale
high-biomass algal blooms of Prorocentrum donghaiense Lu over
the last two decades (Lu et al., 2005; Li et al., 2009, 2010). Those
toxin producers may lead to fish and shellfish kills, and also
impact human health even at low cell abundance (Geohab, 2010).
Karlodinium veneficum (D. Ballantine) J. Larsen is a very small,
unarmoured dinoflagellate (Ballantine, 1956; Wang et al. 2011)
and has been considered as one of the causative species related to
fish killing events (Ballantine, 1956; Place et al., 2008). K.
veneficum shares the characteristics of the genus of Karlodinium
with a straight apical groove and distinct ventral pore (Daugbjerg
n
Corresponding author. Tel./fax: þ 86 57181963209.
E-mail address: doudinglu@163.com (D. Lu).
et al., 2000). Blooms of K. veneficum were first described in South
Africa (Braarud, 1957; Pieter and van der Post, 1967), and later in
Europe (Bjornland and Tangen, 1979; Nielsen, 1996), North
America (Li et al., 2000; Terlizzi et al., 2000) and Australia
(Ajani et al., 2001; Cosgrove et al., 2000). Very recently, this
species was recorded in the coastal water near Nanji Island of
Zhejiang province, China (Wang et al., 2011). However, K. veneficum
is only poorly recorded in the ECS, most likely due to its small size
and difficulty in identification. The bloom dynamics of this species
are not well understood globally. In this study, we examined its
morphological characteristics, and suggest that K. veneficum is a
species which co-occurs with large scale P. donghaiense blooms and
present its distribution pattern in a stratified water column of the
East China Sea in the spring of 2011.
2. Methods
2.1. Study area
This study was conducted in the ECS between March 29 and
May 27, 2011 (Fig. 1). Five transects (Ra, Rb, Za, Zb and Zc)
between 281N and 311N, normal to the coastline, were sampled in
the coastal area of the ECS. These trasects crossed both the 20 m
and 60 m isobaths.
0967-0645/$ - see front matter Crown Copyright & 2013 Published by Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.dsr2.2013.01.015
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X. Dai et al. / Deep-Sea Research II 101 (2014) 237–243
Fig. 1. Sampling stations and circulation pattern in the East China Sea (ECS) (modified from Zhou et al., 2003; Naimiea et al., 2001). Left panel, YS: Yellow Sea; KC: Kuroshio
Current; TWC: Taiwan Warm Current; CC: Coastal Current (seasonal current northeastward in summer and southwestward in winter); TC: Tsushima Current. Right panel:
closed circles indicate comprehensive stations and open circles indicate hydrological stations, with labels above or below the station symbols, respectively; transect labels
are marked to the right of the transects; dotted lines are isobaths (m).
Two main currents, the Coastal Current (CC) and the Taiwan
Warm Current (TWC) interact in this area. The direction of the CC
varies seasonally with the monsoon (Zhou et al., 2008a). It flows
southwestward when north and northeast wind prevails in winter,
and turns to flow northeastward when north winds become weaker
and southwest winds start to prevail in spring. Both the freshwater
plume of the Changjiang River and the TWC become stronger in
spring, and the latter invades the lower part of water column, a
process which intensifies stratification in the offshore water of the
ECS. The TWC has a higher salinity than that in the coastal area, since
it originates and extends from the Kuroshio Current (KC). There is an
upwelling belt, about 40 km wide, between the 20 m and 50 m
isobaths which runs parallel to the Zhejiang coast line (Luo, 1998; Luo
and Yu, 1998; Qiao et al., 2006).
2.2. Sample collection
Two types of sampling stations were sampled mainly during
daylight hours. Comprehensive stations included hydrological
and biological information, whereas hydrological stations
included only physical information. An SBE 19plus CTD (SeaBird
Electronics Inc., USA) which was interfaced with an in situ
fluorometer (WET Labs, WETStar fluorometer, WS1S-1293) was
used to profile from the sea surface to the bottom of the water
column in order to determine the depth of the chlorophyll
maximum layer (CML, also referred to as the middle layer) before
sampling at each comprehensive station. Water samples were
collected using 30 L Niskin bottles in the surface layer, CML and
bottom layer. Extra sampling depths were added at selected
stations. Water samples (500 mL) for phytoplankton analysis
were transferred into 550 mL polyethylene terephthalate (PET)
bottles and were then fixed with 3–5% acidic Lugol’s solution.
Environmental parameters, such as temperature, salinity, density,
dissolved oxygen (DO) and chlorophyll-a (Chl-a) were recorded at
every station at 0.5 m depth intervals using the CTD probe.
2.3. Species isolation and culturing
Naturally occurring K. veneficum cells were isolated from
samples taken within the investigated area during its bloom time
in May, 2011. Approximately 1.5 L of sample was screened
through a 20 mm plankton net to remove larger plankton cells.
Small amounts of this were then added to a series of glass tubes
containing 10 mL F/2 medium (Guillard, 1975). The modified
dilution method (Throndsen, 1978) was used for isolating a single
cell. Strains were maintained in F/2 medium at a salinity of
30 g kg 1 at 20 1C and under a 12:12 h light:dark cycle with an
approximately 810 lx illumination.
2.4. LM and SEM observation
Living cells of K. veneficum were observed using an Olympus CX31
(Olympus, Tokyo, Japan) and micrographs were taken using a Leica
DFC 420 digital camera that was attached to a Leica DM 2500
microscope (Leica, Wetzlar, Germany). Young age cells from clonal
cultures were immobilized in Lugol’s solution and examined under
bright field with the Leica DM 2500 microscope. Cell length and
width were measured from 50 cells in mid-exponential growth phase
that were photographed using a calibrated objective. The chloroplasts
and nucleus were observed and photographed with a fluorescence
microscope Leica DM5000B (Leica, Wetzlar, Germany).
For scanning electron microscopy (SEM) observations, the culture
was first concentrated by gentle centrifugation (Bolch et al., 1999),
then 0.5 mL of the condensed culture was fixed by adding an equal
volume of 4% OSO4 (made up with culture medium) for 1.5 h at room
temperature. The fixed cells were then rinsed once with distilled
water, and dehydrated through an ethanol series (10%, 30%, 50%, 70%,
80%, 90%, 95% and 99%), allowing 10–15 min at each step. Finally two
15 min rinses each in 100% ethanol and 100% dry acetone were
carried out (De Salas et al., 2008). The samples were critical-pointdried in liquid CO2 in a Hitachi HCP-2 critical-point-drying apparatus,
and subsequently glued to SEM-stubs and sputter coated with gold.
Sample examination was performed using a Hitachi S-3000N scanning electron microscope.
Field samples were concentrated to 50 mL after sedimentation
for more than 24 h. For observation, 1 mL subsample was transferred to a 1 mL Sedgewick Rafter counting chamber. Cells were
then counted under a light microscope (Olympus CX31) at 100 and 400 magnification. This step was repeated if the plankton
abundance was low.
2.5. Data analysis
Cell abundances (cells L 1) were calculated according to the
equation: cell abundance¼100 Cn/V, where Cn is the number of
cells counted and V (mL) is the volume of the observed
subsample.
X. Dai et al. / Deep-Sea Research II 101 (2014) 237–243
The vertical distribution of K. veneficum along the transect Rb
was analyzed due to a high cell abundance observed at station
Rb12. Additionally the vertical distribution of chlorophyll, salinity
and temperature were contoured along this transect using Ocean
Data View (http://odv.awi.de/). The horizontal distribution of
K. veneficum was contoured using the Surfer (Version 8.0, 2002,
Golden Software, Inc.) based on the biological information from
comprehensive stations.
3. Results
3.1. Morphology of the targeted species
Cultured cells of the targeted species had a mean length of
13.6 71.2 mm (range 11.0–15.8 mm) and a mean width of
10.07 1.1 mm (range 8.0–12 mm) (n ¼50). The cell shape was
oval, with the epicone and hypocone being of about equal size
(Fig. 2). The sulcus extension invading the epicone was clearly
visible (Fig. 2a). There are four chloroplasts, two in the epicone
and two in the hypocone (Fig. 2b). The nucleus was large and
round, and was located in the hypocone (Fig. 2c). Observations
under the SEM showed that the cell body of K. veneficum is
composed of a conical or rounded epicone and hemispherical
hypocone. The sizes of both parts were nearly equal. In ventral
view, the cingulum displacement was about 30–38% of the body
length. One transverse flagellum comes out from the central point
of ventral view. The sulcus extended onto the epicone (Fig. 2d).
239
The ventral pore of K. veneficum was clearly visible and was
located in the left of the apical groove with a size about 0.8 mm
(Fig. 2d and e). A distinct apical groove was found at the top of
epicone which extended straight from the apical ventral side to
the dorsal side (Fig. 2e).
3.2. Vertical and horizontal distribution of K. veneficum
In April 2011 cell abundance of K. veneficum population was
low (1000–1600 cells L 1) along transect Rb when the water
column was not distinctly stratified (Fig. 3). Cell densities of the
K. veneficum population increased rapidly when the water column
stratification intensified in early May (Fig. 4). An intense bloom of
K. veneficum occurred at station Rb12 on May 13, 2011, within a
well-stratified water column (Fig. 5). At this stage, most of the
cells were located in the upper 10 m layer of the water column
(Fig. 5). Chlorophyll was relatively higher within the bloom than
in the adjacent zone (Fig. 5). An upwelling, which was indicated
by high salinity and temperature and originating from the TWC,
impacted the water column from the bottom layer (Figs. 3–5).
K. veneficum was registered at 12 stations in the surface layer,
15 stations within the middle layer and at 2 stations in the
bottom layer. Two cell aggregates of K. veneficum were observed
between May 13 and May 15, 2011. One was located around
122.91E 30.01N (near Zhoushan Island) and the other in 122.21E,
28.81N (Fig. 6). In the northern aggregation the K. veneficum cell
abundance was higher within the surface layer than in the middle
layer. The highest cell concentration reached 3 107 cells L 1 at
Fig. 2. Micrographs of Karlodinium veneficum. (a) Cell showing the sulcal extension (arrow, bright field (LM)); (b) cell showing chloroplasts, (arrow, epifluorescence (LM));
(c) cell showing the nucleus located in the hypocone (arrow, epifluorescence (LM)); (d) ventral view showing the ventral pore, flagellum, cingulum displacement and sulcal
extension (arrow (SEM)); (e) apical view showing the apical groove and ventral pore (arrow(SEM)). SE: sulcal extension, AG: apical groove, VP: ventral pore, CD: cingulum
displacement, FL: flagellum, CI: cingulum. Scale bar is 5 mm.
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X. Dai et al. / Deep-Sea Research II 101 (2014) 237–243
Fig. 3. Distribution of K. veneficum cell abundance, chlorophyll-a, salinity and temperature along transect Rb on April 19, 2011.
Fig. 4. Distribution of K. veneficum cell abundance, chlorophyll-a, salinity and temperature along transect Rb on May 4, 2011.
Fig. 5. Distribution of K. veneficum cell abundance, chlorophyll-a, salinity and temperature along transect Rb on May 13, 2011.
X. Dai et al. / Deep-Sea Research II 101 (2014) 237–243
241
Fig. 6. Distribution of K. veneficum in the surface layer (left panel) and middle layer (right panel) in the ECS during May 13–15, 2011. Unit: cells L 1.
the surface layer in station Rb12. In the more southern one, cell
densities were lower, about 800–75,000 cells L 1, and a wider
and higher cell abundance distribution of K. veneficum was
observed in the middle layer.
4. Discussion
K. veneficum is a cosmopolitan species but has rarely been
detected in the field, partly due to its small size and the fragile
nature of the cell (Wang et al., 2011). Its morphology was first
described by Ballantine (1956): an ovoid cell with a length 9–
18 mm; chromatophores golden brown, irregular in shape, varying
in number from 2 to 8, usually 4, equally in epicone and
hypocone. In this study, there was no significant difference in
cell size, except that cells had a larger size during cell division
stages. Other characteristics, such as the number of chloroplasts
and the shape of the epicone, hypocone and nucleus, were
consistent with the description by Ballantine. The species in the
investigated water column had the distinct characteristics of the
Karlodinium genus, with a straight apical groove and distinct
ventral pore (Daugbjerg et al., 2000). It is obviously different
from Takayama which has an ‘‘S’’ shape apical groove, and also
from Karenia which has no ventral pore (De Salas et al., 2008;
Wang et al., 2011).
Daugbjerg et al. (2000) considered that plug-like structures in
hexagonal configuration in the amphiesma and lenticular pyrenoids were the specific structures of K. veneficum. Additionally, the
chloroplast pigments are fucoxanthin or fucoxanthin derivatives
rather than peridinin for this species. Other characteristics, like cell
size, chloroplast number, nucleus location, apical groove length
and ventral pore shape, help to distinguish the species within the
genus (Bergholtz et al., 2005; De Salas et al., 2008; Garcés et al.,
2006). For example, Karlodinium decipiens, Karlodinium antarcticum,
and Karlodinium conicum have much larger size; the apical groove
is very short and many chloroplasts are peripheral and highly
pigmented for Karlodinium ballantinum; the nucleus is large,
occupying much of the right side of the cell, with indistinct
margins for Karlodinium corrugalum, but it is relatively small, near
the cell antapex for Karlodinium conicum, and it is median, indistinct except prior to cell division for Karlodinium vitiligo (Bergholtz
et al., 2005; De Salas et al., 2008); Karlodinium armiger has many
chloroplasts, mean 8 range 2–16 (Bergholtz et al., 2005; Garcés
et al., 2006). The morphological feature of cells observed in this
study coincided exactly with that of our previous study, which
confirmed the species as K. veneficum both morphologically and
genetically (Wang et al., 2011). In addition, the cultures of the
strain from this study exhibited strong karlotoxins (Zhang, personal
communication). These characteristics suggest that K. veneficum
blooms co-occured with large scale P. donghaiense blooms in spring
2011. However, the existence of some other Karlodinium species in
seawater samples examined with light microscopy is not completely excluded.
K. veneficum has some synonyms, Gymnodinium veneficum,
Gymnodinium galatheanum, Gymnodinium micrum and Karlodinium
mircum (Bergholtz et al., 2005; Daugbjerg et al., 2000), resulting in
confusion in its geographic distribution. In the ECS, Zhou et al.
(2008b) isolated two strains of K. micrum from the eastern region
in 2005 and 2006, with mean length and width 7.1 and 5.7 mm
respectively. these measurements are much smaller than those
reported for K. veneficum in previous reports as well as in this
study. Park et al. (2009a,b) detected K. veneficum in the northern
region of the ECS and the south coastal area of Korea using realtime PCR. Recently, Wang et al. (2011) detected K. veneficum in
the coastal water near Nanji Island in 2009 (Wang et al. 2011),
which was close to the southern aggregated center in the ECS
observed in this study. These results show that K. veneficum is
widely existent in the ECS, but the first recorded blooms of K.
veneficum are presented in the current study.
The K. veneficum population may respond non-linearly to a
given parameter because physical, chemical, and biological parameters often interact in nature. However blooms of this organism
are supposed to be closely related to the water column stratification which provides a relatively stable environment. Many HABs
occur in stratified water columns (Geohab, 2008). Partensky and
Sournia (1986) observed that the distribution of Karenia mikimotoi
was tightly linked to stratified areas in Northern European seas. In
fact, another dinoflagellate, P. donghaiense, often forms large-scale
high-biomass algal blooms in stratified water column in the ECS
(Lu et al., 2005; Zhou et al., 2008a).
The stratified water column in the ECS is considered to result
from the shearing of the Taiwan Warn Current by the freshwater
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X. Dai et al. / Deep-Sea Research II 101 (2014) 237–243
plume from the Changjiang River. Stratification is most distinct in
late spring because both the freshwater plume and the TWC
strengthen (Zhou, 2010). Coincident with the stratified water
column, K. veneficum bloom also occurred in the upwelling zone
where the Zhoushan fishery (291300 –311000 N, western sea
area—1251E) is located. Whether the upwelling supplies favorable temperature and rich nutrients for the bloom is not yet clear,
but both nutrients and temperature are crucial to many HABs
(Anderson et al., 2008; Davis et al., 2009; Zhu et al., 2008).
Furthermore, upwelling and fronts often result in thin layers
which have an aggregation effect on phytoplankton cells (Geohab,
2008; Jackson et al., 2005), which could explain the aggregation of
most K. veneficum cells in the upper 10 m water during the bloom
time observed in this study.
Another factor which could impact the K. veneficum blooms may
be interspecific interactions. During the cruises, no K. veneficum cells
were registered before April. After then, both K. veneficum and
P. donghaiense were found in some survey stations but with low cell
abundance. In May 2011, the P. donghaiense cell abundance
increased quickly and its bloom widely spread close to the 50 m
isobath line. During the P. donghaiense blooms, K. veneficum bloom
occurred near the station Rb12 on May 13, 2011. The exact relationship between these two species is not yet clear. Longer-term studies
will help to answer such questions.
5. Conclusion
Morphological characteristics suggest that K. veneficum is a
bloom species which co-occured with large scale P. donghaiense
blooms in the spring of 2011. The bloom pattern appeared closely
related to water column stratification.
Acknowledgments
This study was supported by National Science Foundation
(41176141),
CEOHAB-II—the
National
973
Program
(2010CB428702; 2010CB428704), Foundation of Key Laboratory
of Integrated Monitoring and Applied Technologies for Marine
Harmful Algal Blooms, SOA (MATHAB20100310) and the scientific
research fund of the Second Institute of Oceanography, SOA
JG1029.
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