Tidal activity pattern and feeding behaviour of the ophiuroid Ophiocoma scolopendrina on a Kenyan reef flat

Ophiocoma scolopendrina exhibits a distinctive pattern of feeding activity on intertidal reef platforms off Kenya. With the first wave of the flooding tide, dense aggregations of these ophiuroids (up to 320 m^-2) engage in a 1-2 min burst of surface-film feeding, vigorously sweeping the air-water interface and associated sea foam with the ventral surface of 2-4 arms. Suspension feeding (with arms extended in the water column) is the primary feeding mode throughout the rest of the tidal cycle (involving 25-65% of the population at a time), while bottom feeding (with arms extended along the substratum) is infrequent (< 10%). Field experiments showed that surface-film feeding is regulated by water depth and can be triggered by suspended particles. This feeding mode appears to be an adaptation to the intertidal habitat, enabling the ophiuroids to exploit a nutrient-rich surface film during a temporal refuge (low tide) from fish predation. Dense populations of O. scolopendrina may represent an important trophic link between producers of particulate organic material and higher-level consumers in coral reef environments.