The relationship between Diadema corallivory and macroalgae in a high-latitude coral community in Japan

Abstract

Destructive corallivory by Diadema spp. on acroporid corals was observed in high-latitude coral communities in Japan, where high algal abundance is generally observed in winter and spring. Primarily an herbivore Diadema turns omnivorous during times of food shortage, suggesting that corals could become an alternative food source for Diadema spp. when algae become scarce. This hypothesis was examined by quantifying algal abundance, Diadema abundance, and Diadema feeding scars on corals in the remnant coral population along the coast of Uchiura, Shizuoka, Japan. The number of feeding scars was correlated with the density of Diadema, which increased when algal abundance decreased; however, there was no correlation between algal abundance and numbers of feeding scars on corals. Thus, the hypothesis that corals are an alternative food source for Diadema spp. was partially confirmed, although examination of Diadema gut content composition could help verify whether the frequency of corallivory is inversely correlated with algal abundance.