Foraging behavior, substrate preference and influence of Echinometra sp. A on the carbonate budget of Nukubuco Reef, Fiji Islands

Bioerosion can be important to the configuration and destruction of coral reefs. Echinoids as grazers and burrowers can contribute significantly to coral reef destruction. The rock-boring sea urchin, Echinometra sp. A has colonized extensive areas of dead coral on the Nukubuco reef, Fiji. This study provides data on rates of bioerosion of the reef structure using gut analysis and how these rates vary among size classes of Echinometra. It also provides information on the distribution and behavior of different size classes of Echinometra. This is pertinent to Micronesia and the rest of the tropical Pacific because Echinometra is usually the most prevalent species on the coral reefs. Field sampling on size-specific behavior showed small and medium urchin dominance on the crests engaged chiefly in burrowing and feeding behavior while the flats demonstrated urchins from all representative size classes engaged in feeding, burrowing and scouring. This difference was a reflection of difference in environments. Echinometra sp. A showed a preference for coral rock due to the brittle framework it provides to make burrows and due to the availability of turf algae infested on the dead coral for food. In feeding on algae, it also removes a large portion of coral (CaCO3) substrate. Bioerosion rate was lower on the Nukubuco flats 0.20 x 10–3 kg CaCO3 /urchin/d, compared to the crests, 0.39 x 10–3 kg CaCO3 /urchin/d. These rates compare closely with studies done on the turnover of gut contents by the two major burrowing echinoids on Enewetak Atoll (Echinometra mathaei and Echinostrephus aciculatus).