Houlbrèque, F. 2004 - feeding by scleractinian corals study. PhD these, Paris VI University, 200 p.

ABSTRACT

This study discusses feeding by scleractinian corals. First of all, I estimate the uptake of pico- and nanoplankton by corals and benthic reef organisms using both laboratory and field experiments. Results show that, under controlled conditions, different Scleractinian corals, symbiotic or asymbiotic, are able to consume pico- and nanoplanktonic cells (bacteria, cyanobacteria and flagellates). Among these micro-organisms, nanoflagellates are the most important group, contributing between 84 and 94% of the total ingested carbon and between 52 and 85% of the total ingested nitrogen, depending on coral species. Pico- and nanoplankton ingestion therefore constitutes a significant input of nutrients, providing as much nitrogen as dissolved sources. During an in situ experiment on the reef of La Prévoyante (Mayotte Island, Indian Ocean), dominated by Scleractinian corals, I observed that phytoplankton concentrations (total chlorophyll, Prochlorococcus, cyanobacteria, picoeukaryotes) as well as micro-heterotrophs (bacteria, nanoflagellates, ciliates) were depleted by 29 to 39% above the reef compared to the adjacent open waters, suggesting a significant removal by reef microorganisms. This uptake represent an input of 17 mmoles N m-2 j-1 and 125 mmoles C m-2 j-1 for the reef community.
Under laboratory conditions, I have also quantified the effect of feeding on different physiological parameters such as calcification, photosynthesis and tissue growth. Feeding significantly changes the main physiological parameters, with a simultaneous increase in chlorophyll and protein concentrations, zooxanthellae density and rates of photosynthesis. The major result of this work is that feeding increase both dark and light calcification rates, as well as dark and light synthesis of the organic matrix. The increase in the rates of calcification in fed corals might therefore be due to a feeding-stimulation of organic matrix synthesis. Several hypotheses are suggested to explain this stimulation.

KEY-WORDS : Scleractinian corals - Stylophora pistillata - Heterotrophic nutrition - Nanoplankton - Picoplankton - Grazing rates - Photosynthesis - Calcification