Feeding mechanisms and feeding strategies of Atlantic reef corals

Abstract

The feeding behaviour of 35 species of Atlantic reef corals was examined in the laboratory and in the field. Observations were made during the day and at night, using freshly hatched brine shrimp nauplii and finely ground, filtered fresh fish as food sources. Three feeding strategies were observed: Group I–feeding by tentacle capture only; Group II–feeding by entanglement with a mucus net or mucus filaments; Group III–feeding by a combination of tentacle capture and mucus filament entanglement. Group I included corals of the families Poritidae and Pocilloporidae which were normally expanded during both day and night. Group II included corals of the family Agaricidae which were normally expanded at night and contracted during the day. Group III included corals of the other families examined which, with the exception of Dendrogyra cylindrus, were normally expanded only at night. Feeding responses were elicited by both chemical and tactile stimuli. A preparatory feeding posture was assumed in response to chemical stimuli and consisted of horizontal positioning of the tentacles, elevation of the oral disk to form a cone‐like mouth, a wide mouth opening and secretion of mucus by the epidermis of the oral disk. Following the assumption of the preparatory feeding posture, food capture and ingestive movements were elicited by tactile stimuli. However, food capture and ingestive movements were also elicited by chemical stimuli alone in those species which were normally contracted during the day. While expanded corals captured food with their tentacles or with mucus filaments, contracted corals were able to feed by capturing fine particulate matter with mucus filaments only and thus acted as suspension feeders. By a combination of feeding strategies, reef corals were able to feed both day and night and a wide range of potential food ranging from fine particulate matter to large zooplankton was available to them.

Perspectives on mucus secretion in reef corals

“…The strings are then conveyed to the mouth by mucociliary action. Other workers (Lewis & Price 1975, Lewis 1977, Goldberg 2002 showed that several Atlantic corals species were able to act as suspension feeders by means of mucous nets and strands, which were subsequently drawn into the mouth. Lewis (1977) argued that the ability of reef corals to feed by mucous nets greatly increased the potential food resource available to them.…”

Particle capture mechanisms in suspension-feeding invertebrates

“…This observation is supported by Sponaugle (1991) who studied the flow patterns and velocities around the tentacles using a scale model of the gorgonian polyp. Readily observable zooplankton captured by polyps has overshadowed the fact that corals do form mucus nets that capture suspended particulate matter (Lewis & Price 1975, Lasker 1981). Thus, Roushdy & Hansen (1961) showed that the octacoral Alcyonium digitatum is able to ingest and assimilate diatoms by means of a mucus net (Skeletonema costatum).…”

Calcification by juvenile corals under heterotrophy and elevated CO2

“…Corals in fed treatments were isolated (every night for 2 weeks, every other night for the third week) for 3 h in 12.5 cm x 12.5 cm x 3 cm plastic containers filled with seawater from their respective treatment tanks and provided with 24-h-old Artemia nauplii (brine shrimp). Feeding took place at night, shortly after lights were switched off to mimic crepuscular feeding and temporal zooplankton abundance observed in local coral reef environments (Lewis and Price 1975). Unfed corals were not provided nauplii during the 3-week experiment and were not isolated in empty feeding containers.…”