Predation by xanthid crabs on early post-settlement gastropods: the role of prey size, prey density, and habitat complexity

Abstract

Abstract Small predators in marine benthic communities create a hazardous environment for newly settled invertebrates, especially for the smallest individuals. To explore the effects of predation on a newly settled gastropod, queen conch ( Strombus gigas Linnaeus), by a xanthid crab ( Micropanope sp.), prey size, prey density, and habitat complexity were manipulated in five laboratory experiments. All crabs >3.1 mm CW killed all conch 5.0 mm CW, however, killed conch that were >5.0 mm SL, suggesting that conch may reach a size refuge from xanthid crabs at 5 mm SL. Furthermore, when given a choice, crabs (4.8 mm CW) preferred smaller conch (2.0 mm SL) to larger (3.7 mm SL), suggesting that 1 week of additional growth in shell length is advantageous to survivorship. Proportional mortality decreased as conch density increased when crabs were offered conch at seven different densities (two to 96 individuals). Crabs proved to be effective predators regardless of the amount of seagrass structure provided in a microcosm experiment, and could consume two conch in 10 s. The high densities of xanthid crabs that occur in the wild, their effectiveness as predators, and their large appetites point to the important role that small predators may potentially play in structuring the population dynamics of their small prey immediately after settlement.