Feeding biology of a Hawaiian sea star corallivore, Culcita novaeguineae Muller & Troschel

Abstract

Several traits were examined in four potential coral prey species (colony form, organic matter content, caloric density, tissue accessibility, mucus release, cnidocyst composition, toxicity, and colony defense by crustacean coral guards) to help understand the feeding preference of the Hawaiian asteroid corallivore Culcita novaeguineae Muller & Troschel. In laboratory experiments, C. novaeguineae exhibits a preference for Pocillopora damicornis (L.) and Pocillopora meandrina Dana over Porites compressa Dana, Montipora verrucosa (Lamarck) and Fungia scutaria (Lamarck). The feeding rate of Culcita novaeguineae on Pocillopora damicornis was ≈ 28 cm 2or 250 cm 3 per day. In limited field observations, a preference was shown by Culcita novaeguineae for small colonies of Pocillopora meandrina which were totally killed (all tissues removed from branches) after attack by the sea star. Although the organic matter content (mg dry wt/cm 3) of Pocillopora was the lowest of the four corals, the percent loss of organic matter after feeding (“utilization” by Culcita) was the highest. This high intake of organic matter corresponds with the superficial location of the tissue layers and the ease of removal of tissues (by “water piking”) in Pocillopora compared with the other corals. Small colonies of Pocillopora are eaten more frequently than large colonies; the former harbor relatively low numbers of crustacean guards (crabs and shrimp) and their guards are small compared with large colonies. Coral mortality caused by Culcita ( 1.0 m 2/yr) is only about one-fifth of that by Acanthaster (5.3 m 2/yr), but the selective feeding of Culcita on Pocillopora, and its avoidance of nonpocilloporid corals, could affect significantly the relative abundance of corals in Hawaiian reef assemblages.