Bioerosion potential of three species of sea urchins commonly found in the reef flats of Eastern Mactan Island, Cebu, Philippines
2001
Uy, F.A. | Bongalo, J.N.C. | Dy, D.T. (University of San Carlos, 6000 Cebu City (Philippines). Marine Biology Section)
Echinoids are relatively common in tropical reef flats. They are also major bioeroders. The bioerosion potential of three common echinoids (i.e., Diadema setosum, Echinometra mathaei, E. oblonga) commonly found in reef flats off eastern Mactan Island, Cebu, Central Philippines was estimated by quantifying the numerical density and the average egestion rate of CaCO3 per individual per unit time of a given species. The amount of CaCO3 in the gut of the three species was also quantified. Of the three species of sea urchins, D. setosum (mean plus or minus SE; 2.6 plus or minus 0.71 ind/sq m) was more abundant than E. mathaei (0.9 plus or minus 0.27) or E. oblonga (0.1 plus or minus 0.04). D. setosum and E.mathaei appeared to form distinct clumps compared to E. oblonga. Bioerosion rate was higher for D. setosum collected at non-seagrass areas (0.51 plus or minus 0.69) compared to specimens collected at seagrass areas (0.15 plus or minus 0.04). The mean bioerosion rate of D. setosum was 0.33 g CaCO3/urchin/d. This value was lower compared to that of E. mathaei (0.42) but higher than that of E. oblonga (0.22). The three species of sea urchin had significantly varying amount of CaCO3 content in their gut. D. setosum collected in non-seagrass areas have significantly higher CaCO3 content in their gut (1.0 g CaCO3/ind) compared to D. setosum collected in seagrass areas (0.22) and the two Echinometra species (0.52 for E. mathaei and 0.27 for E. oblonga). Extrapolating the results, D. setosum has the highest bioerosion rate (142-483 g CaCO3/sq m/yr followed by E. mathaei (138) and then by E. oblonga (8). The value pooled together is roughly 10% of calcification rate of a tropical coral reef flat
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