Microscale flow dynamics and particle capture in scleractinian corals: I. Role of the tentacles

Abstract

AbstractThe size, shape, and arrangement of tentacles in scleractinian coral polyps are likely to affect particle capture yet have not been investigated in a systematic way. Morphometric measurements of tentacles of several coral species found in the Caribbean Sea were taken from macro-photographs, and from these, models were constructed in three postures: straight, upstream-facing, and downstream-facing. These models were placed in a flume to video the flow paths of particles around them. Video analysis indicates tentacles, and their specific postures, have a dramatic effect on micro-flow patterns. The expanded soft tissue tentacles, and their specific postures, greatly increase probability of particle capture by direct impaction, inertial impaction, and gravitational deposition. All tentacle postures cause increased retention time relative to freestream travel in their immediate proximity, as well as increasing both contact with the tentacle surface, and tumbling of particles. Straight and upstream-facing tentacles deflect particles downward to their base, while downstream-facing tentacles deflect particles upwards. When results from individual tentacles are considered in geometric combination, the secondary radial symmetry of the tentacular whorls in simple coral polyps appears to be an optimal strategy to filter suspended particulate material in an oscillating and omni-directional flow environment. In meandrine corals, the hedgerows of straight and curved tentacles appear to draw particles downward, retain them, and direct them onto the oral feeding areas below the thecal ridges. The size, shape, and arrangement of tentacles are thus of key importance in understanding suspension feeding in scleractinian corals.