Coral and algae cover with respect to abundances of the

Spatial-Temporal Analysis of Coral and Algae Cover
with respect to Abundances of the Sea Urchin Diadema
antillarum in 5 sites of Puerto Rico
Alfredo Montañez- Acuña; Alex Mercado-Molina; Samuel Suleiman; Roberto Colón
Sociedad Ambiente Marino
P.O. Box 22158 San Juan, P.R. 00931
E-mail: alfredo_13_bb@yahoo.com
Introduction:
There has been a decline of coral reefs in the
Caribbean region. One of the main reasons for this
decline is the loss of the grazer Diadema antillarum,
which has been recognized as a key species in coral
reefs due in part to its habits of macroalgae
consumption. This selective behavior play an
important role in controlling abundance and
distribution of algae and promoting coral recruitment
by keeping substrate free of algae and available for
colonization. The objective of this study was to relate
the abundance of the Diadema antillarum to that of
the coral and algae cover in 2009 and 2010 at five
sites around Puerto Rico.
Statistical Methods:
The algae and coral cover were assessed by superimposing a
total of 100 random points on each quadrat image using the
CPCe® software. Kruskal-Wallis One-way ANOVA was
performed to test if densities of D. antillarum differed
significantly among sties. Similarly this test was used to
compare coral and algae cover among sites. In addition, a
correlation analysis was performed to explore if there was a
relationship between algae cover and coral cover at the study
sites during the study period.
Results:
Results indicate that algae cover differed significantly
(p<0.05) between the study period for all study sites,
decreasing in PN and PA while increasing at ESC, TAM, and
PS. The study site that showed higher algae cover was in
2010 at ESC (96%) and lower 12% at PA. On the other hand,
comparison of coral cover within sites between study periods
indicates a decrease in all sites studied from 2009 through
2010. Coral cover differed significantly only at PA and PN
between 2009 and 2010(p<0.05). ESC, TAM and PS showed
no significant difference (p>0.05) between 2009 and 2010.
For 2009, mean coral cover was significantly higher at PN
with 30% and lower 2.6% in ESC. For 2010, the study site
that showed more coral cover was TAM (19%) and the lower
was PA with 0.4%.
Figure 1: Diploria spp surrounded by Diadema antillarum
Figure 5: Correlation between coral and alga cover in 2009 (up)
and 2010 (down). Data of all sites pooled.
Correlation analysis indicates that there was significant
relationship between coral cover and algae cover in
2009 (r=0.43, p=0.00018) but not in 2010
(r=0.18,p=0.07). On the other hand, as the mean
density of D. antillarum increases, algae cover
decreases whereas coral cover increases. However,
both of these relationships were not significant
(p>0.05).
Methods:
The study was carried out in 5 sites in Puerto Rico:
Puerto Nuevo (PN), Escambron (ESC), Playa Azul
(PA), Tamarindo (TAM), and Punta Soldado (PS). At
each site, sea urchin densities were assessed by
placing five 20m2 belts transects at similar depth (0 to
3 m) were placed randomly to provide true data.
Within each transect five 1m2 quadrat were placed (25
total) to assess coral and algae cover.
Figure 3-4: Bar graph with standard deviation showing a comparison of median coral
and algae cover at study sites between study period.
1
2
3
4
5
Figure 9-10: Correlation between D. antillarum density and coral/algae
cover in 2009 (up) and (down). Data of all sites pooled.
Discussion:
Results indicate that the relation between coral and
algae cover is not as simple as an inversely
proportional relation as suggested by other studies
and that Diadema antillarum did not play a
significant role in enhancing coral cover or reducing
algae cover at the studied sites.
Figure 2: Study sites in Puerto Rico
LEGEND: 1=PUERTO NUEVO, VEGA BAJA
2= ESCAMBRON, SAN JUAN
3= PLAYA AZUL, LUQUILLO
4= TAMARINDO, CULEBRA
5= PUNTA SOLDADO, CULEBRA
Figure 5-6: Bar graph with standard deviation showing a comparison of median cover
between study sites in 2009 (left) and 2010 (right).
Acknowledgements: A special recognition to all SAM members who helped gather data for this project and to CREST-CATEC who funded and made this project possible.