Planula release and reproductive seasonality of the scleractinian coral <I>Porites astreoides</I> in Bermuda, a high-latitude reef

Abstract

Planula release from the scleractinian coral Porites astreoides Lamarck, 1816 at a high-latitude reef in Bermuda primarily occurred in the summer months of July and August, when the average seawater temperature for the lunar cycle preceding planulation exceeded 26.5 °C. Within the reproductive season in Bermuda, optimal planulation temperatures for P. astreoides are narrow. The release of fewer planulae was correlated with higher temperatures and there was significant variation in reproductive effort in colonies collected from sites across the 18-km wide Bermuda lagoonal seawater temperature gradient during this 2-yr study. The annual reproductive period of this species lengthens with a decline in latitude, which corresponds to a decrease in the range of annual seawater temperatures. Reproductive effort, as measured by the percentage of the population that is reproductive and number of planulae released per colony, is similar or slightly higher in Bermuda compared to conspecifics at lower latitudes. However, the shortened reproductive season results in a lower overall annual reproductive effort in Bermuda. Lunar synchrony of planula release peaked a few days before the new moon, slightly earlier than conspecifics in Florida, which peak during the new moon. Colonies from the Inner Lagoon peaked in planula release a few days earlier than those from other zones. We attribute spatial variation in lunar periodicity of planula release to differences in the timing of fertilization or planula maturation that may be influenced by environmental factors such as temperature and turbidity.