Reproductive strategies in two closely related stony corals (Agaricia, Scleractinia)

Samples of the scleractinian coral Agaricia agaricites (Limaeus) were studied for time of planula release, planula production and related characteristics. The corals were collected over a 2 yr period on the fringing reef of Curaqao at depths from 5 to 30 m. Two distinct reproductive pattems emerged. Based on these patterns and on consistent differences in skeletal morphology, such as size of calices and n b b e r of septa, the separation of the form A. agaricites humilis Vemll as a distinct species, A. hurnilis, from the other forms of A. agaricites is proposed. A. humilisplanulated throughout the year. A. agaricites shed planulae in spring and summer, a period of increasing sea water temperatures. In A, humilis 78 % of the colonies (N = 133) released planulae within 1 wk after collection, compared with only 26 % ( N = 91) in A. agaricites. Maxlmum diameter of the smallest planulating colonies of A. humilis was about 4 times less (28 mm) than in A. agaricites (108 mm). Planula production per unit living tissue area was 4 times larger (0.86 planulae cm-2 wk-') in A. humilis than in A. agaricites (0.23 planulae cm-2 wk-l). However, planula volume was 5 times lower (0.166 mm3) than in A. agaricites (0.860 mm3). It appears that A. humilis employs an opportunistic reproductive strategy compared with A. agaricites. A. humilis is mainly confined to the shallow reef flat and drop off zone (5 to 12 m) and colony diameters rarely exceed 100 mm. A. agaricitesreaches its greatest abundance on the deeper reef slope (10 to 30 m), growing to a maximum size of 600 mm. The differences in reproductive strategies can be explained in relation to the predictability of their habitats.