Nutrient uptake by reef-building corals and the ecophysiological effects

Abstract

Coral reef ecosystems have developed in oligotrophic seawater, but the adjacent land often provides nutrients to the reef water via river and groundwater. In particular, an increasing nutrient level because of anthropogenic nutrient loading has been a serious problem in many coral reefs for a long time. While reef-building corals have adapted with the symbiotic algae (zooxanthellae) to oligotrophic seawater, many previous studies have observed that nutrient enrichment increases the density of zooxanthellae and the algal photosynthetic rate per unit surface area of the coral. However, the effect of nutrients on coral growth (calcification) is not still well understood, and one of the reasons may be that unrealistically high nutrient conditions have been applied in many laboratory studies. In this paper, the uptake and assimilation processes of inorganic nutrients by reef-building corals were categorized for each nutrient species, and the roles of host corals and zooxanthellae and the factors that influence the nutrient uptake rate were summarized. Then, the ecophysiological effects of nutrient enrichment on coral-algal symbiotic metabolism have been reviewed from the perspective of anthropogenic eutrophication of coral reefs.