Prey capture by a benthic coral reef hydrozoan

Abstract

 The natural diet and prey abundance of the benthic coral reef hydrozoan Nemalecium lighti, a common tropical species, were studied by analysing the gastrovascular 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 Blas Islands (Panamá). Prey size ranged from 5 to 550 μm, with invertebrate larvae being the main contributor to the diet of the species. 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 species. Such rates would allow for high production rates for Nemalecium lighti, consistent with reports of the species’ fast growth and high reproduction rates. The observations suggest that some hydrozoans may be active heterotrophic components in coral reef ecosystems.