The influence of tentacle shape, soft -tissue polyp, and corallite morphology, on microscale currents over corals, and implications for particle feeding: A physical model approach.

摘要

Surface soft tissue structures and corallite morphology were measured from in situ macro-photographs of 28 Caribbean corals. Hydrodynamically similar models of tentacles (straight, forward-curved, backward-curved, and sweeper ), two polyp types (simple and meandroid ), as well as prominent corallites of five species (Montastrea annularis, Agaricia agaricites, Siderastrea , siderea, Acropora cervicornis, and Leptoseris cucullata) were constructed. Micro-flow patterns over and around these models were video-recorded in a laminar flume to quantify patterns of particle motion over these models.;Tentacles increased particle retention time in their immediate proximity, contact probability with their surface, and tumbling. In addition, straight and forward-curved tentacles deflect particles downward to their base, while backward-curved tentacles deflect particles upwards.;Particles encountering a simple coral polyp are retained, slowed down, and spread laterally. When polyps are closely spaced, particles tend to stay within the tentacle canopy with almost certain impact. The tentacular radial symmetry of simple polyps, the column flexibility, as well as its retractability, makes simple polyped species particularly well adapted to shallow, omni-directional, high-flow reef habitats. Only a few simple polyped species are found in deep, uni-directional, low-flow environments, and they tend to have limited polyp column expansion, large tentacles, and a wide oral disk, suggesting that their trophodynamics include gravitational deposition.;In meandroid corals the thecal wall is the dominant influence on particle flow over these corals whether it is contracted or expanded. In mid-reef areas meandroid species proliferate, their hedgerows of tentacles form effective zooplankton entrapment canopies. However, in deeper areas, where flow is slower, plate-like species with minimal tentacle expansion, and wide inter-thecal ridge distances become common. Thus, these species appear to strategically shift from intercepting particles moving horizontally to particles falling vertically out of suspension.;Corals with minimal soft tissue expansion generally have prominent corallites and although they are most common in high-energy shallow areas, they are found across the entire reef profile. The corallite models indicate that these solid structures produced micro-flow patterns similar to expanded soft tissue feeding structures, by increasing particle retention, reducing velocity, and increasing lateral spread. The small micro-tentacles (>1mm), common to these species, are believed to secure small live seston.