Growth of a temperate coral: effects of temperature, light, depth, and heterotrophy

The effects of temperature, light, food availability, depth, and season on growth and chlorophyll a (chl a) concentration in the temperate scleractinian coral Oculina arbuscula were experimentally examined in the laboratory and field. The coral has a wide temperature tolerance, but growth was significantly greater at summer than at winter temperatures. Light and a zooplankton food source both contributed significantly to chl a concentrations and to coral growth, with effects on growth being approximately additive. In both lab and field assays, growth and chl a concentrations at the end of the experiment had identical rankings among treatment means, suggesting that increased colony growth may be linked to increased concentrations of chl a. In the field, corals grew significantly better in shallow than in deep water when competing seaweeds were removed. However, coral distribution at 2 sites was concentrated in deeper, darker waters where growth should be slower, rather than In shallower areas where growth potential is higher Thus, 0 arbuscula is less abundant in habitats to which it is physiologically better suited, suggesting that biotic, rather than physiological, rigors may restrict its distribution on local scales.