Effects of temperature, irradiance, salinity and inorganic nitrogen concentration on coral zooxanthellae in culture

Abstract

Effects of temperature, irradiation, salinity and inorganic nitrogen concentration on two cultured strains of zooxanthellae isolated from the corals Pocillopora damicornis (strain P) and Montipora verrucosa (strain M) were studied. Each strain showed different growth responses in terms of temperature and light intensity. A maximum growth rate of strain P, 1.2 per day, was observed at 32°C under all light intensities examined (5-40 μEm^-2s^-1). However, its photosystem 2 activity (FRI) was higher at 28°C than at 32°C under most light intensities. In contrast, the growth rate of strain M was affected more by light intensity and was almost invariably affected at all temperatures examined (24-36°C). Both algal strains had a comparable growth rate and FRI at salinities from 20 to 35 PSU under moderate temperature and irradiant conditions. High temperature and low irradiation reduced the algal tolerance against low salinity. The gross photosynthesis per cell was not affected by the ammonium enrichment more than 5 μM per day although the cellular chlorophyll a content and cell density increased in proportion with the ammonium enrichment up to 20 μM per day. A potential response of zooxanthellae to the multiple environmental stresses was shown from these results.