THE TEMPORAL PATTERN AND RATE OF RELEASE OF ZOOXANTHELLAE FROM THE REEF CORAL POCILLOPORA-DAMICORNIS (LINNAEUS) UNDER NITROGEN-ENRICHMENT AND CONTROL CONDITIONS

The rate of loss of zooxanthellae from intact Pocillopora damicornis (Linnaeus) was determined for colonies growing in laboratory tanks supplied with either ambient seawater or seawater enriched with dissolved inorganic N. Algal release peaked during midday in both treatments. Corals in N-enriched water released 40% more algae . U-1 surface area . day-1 than did control corals. However, algal densities in the N-enriched corals were three times higher than in controls, so specific release rate was lower for N-enriched corals. Lipid content of the N-enriched corals was also lower than in the controls. These results suggest that N enrichment results in: greater algal standing stock and a reduced rate of transfer of photosynthate to the host. N enrichment more than doubled algal densities in this coral indicating that zooxanthellae in situ may be nutrient limited and that algal densities are, to some extent, a function of nutrient levels in the external environment and not entirely regulated by the host.