Prey capture by a benthic coral reef hydrozoan

The natural diet and prey abundance of the benthic coral reef hydrozoan Nem alecium lighti, a common tropical species, were studied by analysing the ga strovascular contents of polyps. Prey capture was estimated from 10 samples collected at 3-h intervals during a single diel cycle (1-2 September, 1995 ) in the San Bias Islands (Panama). Prey size ranged from 5 to 550 mu m, wi th invertebrate larvae being the main contributor to the diet of the specie s. Prey items were found in 56-88% of the polyps over the entire diel cycle . Gastrovascular contents varied between 0.93 and 2.13 prey items per polyp . These capture incidences are among the highest reported for cnidarian spe cies. Such rates would allow for high production rates for Nemalecium light i, consistent with reports of the species' fast growth and high reproductio n rates. The observations suggest that some hydrozoans may be active hetero trophic components in coral reef ecosystems.