Influence of the population density of zooxanthellae and supply of ammonium on the biomass and metabolic characteristics of the reef corals Seriatopora hystrix and Stylophora pistillata

Abstract

In May 1987, the population density of zooxanthellae in the reef coral Seriatopora hystrix around Lizard Island (Great Barrier Reef) varied within and between colonies. This naturally occurring variability made it possible to examine the effect of the population density of zooxanthellae on the physiological characteristics of S. hystrix and its zooxanthellae. As the population density of zooxanthellae increased, the chlorophyll a content and maximum rate of photosynthesis of the zooxanthellae decreased. Phytoplankton studies suggest that cellular chlorophyll content will increase if cells are self-shaded or will decrease if cells are nitrogen-limited. To test the hypothesis that zooxanthellae in S. hystrix and Stylophora pistillata are nitrogen-limited at their highest population densities, colonies of S. hystrix and S. pistillata with high densities of zooxanthellae were incubated in aquaria to which ammonium (ca 10 to 40 mu M) was added at regular intervals.