Microbial utilization of coral mucus in long term in situ incubation over a coral reef

The purpose of this study was to assess degradation and utilization of the mucus produced by 3 coral reef Anthozoa (Sarcophyton, Fungia and Acropora) by microorganisms. This was achieved by carrying out long term in situ incubations at Nouméa lagoon (New Caledonia).The microbial population including bacterial and eukaryotic cells was monitored by cell counts, cultures of mucus degraders, and by estimation of microbial activity from the pool of adenylates and enzymatic activity. In addition the chemical composition (C and N) of the mucus was monitored and its morphological features were observed by scanning electron microscope (SEM).Only slight differences were found between the 3 types of mucus studied. On the whole, they follow the same pattern of change. After a short bacterial growth phase (4 days), a bloom of eukaryotes (Flagellates, Ciliates and Diatoms) was observed. This eukaryote population remained constant for at least 10 days. A similar pattern has been described in the breakdown of detritus of plant origin.Several observations suggest that bacteria utilize only certain components of mucus, the most widely used being proteins, triglycerides and wax esters; these latter two compounds are known to be the dissolved photosynthetic products released by zooxanthellae during mucus secretion. Neither bacteria nor eukaryotes completely degrade the mucus web even after 21 days of incubation. The likelihood that mucus excretion is a defensive reaction against physical and chemical stresses might explain why mucus is a poor, or even inhibiting medium for the bacterial degraders isolated from the mucus itself.

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