Coral ecophysiology from the perspective of biogeochemical cycles in coral reefs

Abstract

Scleractinian corals play important roles in the biogeochemical cycles of the coral reef ecosystem through coral metabolic activities. In particular, the cycling of dissolved organic matter (DOM) in coral reefs has often been focused on in recent years because of the improvement of the DOM analytical technique. This article summarizes recent findings on DOM in coral reefs and compares the chemical characteristics between DOM released from coral colonies and DOM produced on ecosystem scales. The present review shows that the carbon to nitrogen ratios (C:N ratios) of DOM are in a similar range between coral- and ecosystem-scales in Shiraho Reef, Japan, indicating that the coral colonies might be one of the major DOM producers. The efficient nitrogen recycling in coral-algal symbiotic colonies has also been demonstrated in recent years and this explains why corals can release nitrogen-rich DOM, even though the ecosystem is filled with oligotrophic seawater. A series of these biogeochemical and ecophysiological studies would provide a better understanding of the mechanisms which have been maintaining coral reef ecosystems.