A new passive collector to assess settlement rates, substrate selection and predation pressure in decapod crustacean larvae

Abstract

Quantitative sampling and experiments evaluating larval settlement of marine invertebrates require an effective, highly replicable sampling unit. Artificial collectors, cages and solid trays have been used to assess spatial and temporal patterns of postlarval settlement of decapod crustaceans. However, because of problems with sample retention upon retrieval, the interpretation of data from artificial collectors can be problematic. Moreover, the costs and time invested in construction can be high, especially in high-energy subtidal environments where there is a considerable risk of damage and loss. In this study, we describe and test a new passive collector for postlarvae of benthic decapod crustaceans. The device is equipped with a mechanism that covers the collector surface during deployment and retrieval, but exposes it while at rest on the sea bed. The collector design also proved effective in determining settlement patterns, substrate preferences and predation effects. In general, passive collectors are effective in monitoring settlement rates for a diversity of species and therefore will be useful in biodiversity studies. Densities of megalopae closely approximated those in comparable natural habitats collected by diver-based suction sampling. Megalopae exhibited a strong preference for structurally heterogeneous substrates. Megalopal settlement to experimental substrates was statistically the same with and without predator exclusion mesh, indicating that the mesh does not produce undue behavioral artifacts, and that predation pressure was negligible at the experimental sites. These collectors represent a versatile alternative to be applied to a wide variety of questions regarding the settlement and early post-settlement processes in brachyuran crabs, as well as other benthic species and lend themselves well to a variety of manipulative experiments in the subtidal environment.