ZOOPLANKTON CAPTURE BY 2 SCLERACTINIAN CORALS, MADRACIS-MIRABILIS ANDMONTASTREA-CAVERNOSA, IN A FIELD ENCLOSURE

Capture of zooplankton by scleractinian corals has been noted for seve ral species, yet quantitative information on rates of capture and diff erential capture by prey taxon has been lacking. We used field enclosu res to examine prey capture for two coral species, Madracis mirabilis (Duchassaing and Michelotti) and Montastrea cavernosa (Linnaeus), on t he north coast of Jamaica (Discovery Bay) in November 1989, February a nd March 1990, and January 1992. M. mirabilis has small polyps and a b ranching colony morphology (high surface/volume ratio), whereas M. cav ernosa has large polyps and mounding colonies (low surface/volume rati o). Corals were isolated from potential prey, then were introduced int o enclosures with enhanced zooplankton concentrations for 15- to 20-mi n feeding periods. Corals were fixed immediately after the experiment to prevent digestion, and coelenteron contents were examined for captu red zooplankton. Plankton pumps were used to sample ambient zooplankto n in the enclosures near the end of each run. Selectivity and capture rates were calculated for each prey taxon in each experiment; both ind ices were high for relatively uncommon large prey, and low for copepod s, which were often the most common items in the plankton. Sizes of zo oplankton captured by both species were generally larger than those av ailable considering all prey taxa combined, but were almost the same f or both coral species, even though the corals' polyp sizes are very di fferent. This occurred primarily because small copepods, with low capt ure rates, dominated most plankton samples. For specific prey species, or group of species, there were few significant differences in size b etween the prey available and the prey captured. M. mirabilis, with sm all polyps, also captured far more prey per unit coral biomass than di d M. cavernosa, with much larger polyps. We hypothesize that the large differences in capture rate of prey taxa are related to escape or avo idance behavior by those potential prey, and to the mechanics of captu re, rather than to any selectivity by the corals.