WATER-FLOW AND PREY CAPTURE BY 3 SCLERACTINIAN CORALS, MADRACIS-MIRABILIS, MONTASTREA-CAVERNOSA AND PORITES-PORITES, IN A FIELD ENCLOSURE

Scleractinian corals experience a wide range of flow regimes which, co upled with colony morphology, can affect the ability of corals to capt ure zooplankton and other particulate materials. We used a field enclo sure oriented parallel to prevailing oscillatory flow on the forereef at Discovery Bay, Jamaica, to investigate rates of zooplankton capture by corals of varying morphology and polyp size under realistic flow s peeds. Experiments were carried out from 1989 to 1992. Particles (Arte mia salina cysts) and naturally occurring zooplankton attracted into t he enclosures were used as prey for the corals Madracis Mirabilis (Duc hassaing and Michelotti) (narrow branches, small polyps), Montastrea c avernosa (Linnaeus) (mounding, large polyps), and Porites porites (Pal las) (wide branches, small polyps). This design allowed corals to be u sed without removing them or their prey from the reef environment, and avoided contact of zooplankton with net surfaces.]Flow speed had sign ificant effects on capture rate for cysts (M. mirabilis), total zoopla nkton (M. mirabilis, M. cavernosa), and non-copepod zooplankton (M. mi rabilis). Zooplankton prey capture increased with prey concentration f or M. mirabilis and M. cavernosa, over a broad range of concentrations , indicating that saturation of the feeding response had not occurred until prey density was over 10(4) items m(-3), a concentration at leas t an order of magnitude greater than the normal range of reef zooplank ton concentrations. Location of cyst capture on coral surfaces was not uniform; for M. cavernosa, sides and tops of mounds captured most par ticles, and for P. porites, capture was greatest near branch tops, but was close to uniform for M. mirabilis branches in all flow conditions . The present study confirms laboratory flume results, and field resul ts for other species, suggesting that many coral species experience pa rticle flux and encounter rate limitations at low flow speeds, decreas ing potential zooplankton capture rates.