Carcinus maenas (Crustacea: Brachyura): Influence of artificial substrate type and patchiness on estimation of megalopae settlement

Settlement patterns of decapod crustaceans are influenced by size, shape and nature of substrates, as well as by species-specific behaviour patterns. Hog's hair filter material is one of the most commonly used artificial substrates in the study of settlement rates. However, the use of hog's hair collectors in settlement studies poses several problems: movement restriction of settled animals, relatively long and complicated laboratory processing time, and cost and decreasing availability. Despite widely used, no consistent investigation has focused on the influence of size and shape of hog's hair collectors on rates of benthic settlement. A first experiment was set to investigate the effects of collector patchiness on settlement abundances of Carcinus maenas megalopae. Benthic hog's hair collectors of different sizes were deployed intertidally in the lower Mira Estuary. Settlement was addressed as ind collector^{- 1} and ind m^{- 2} in relation to collector' surface area and perimeter:area ratio. Results showed that collector patchiness significantly influenced settlement response of C. maenas megalopae, which differed according to settlement intensity and measure. Megalopae settlement responded to lower scales of habitat patchiness at high than at low intensity. Settlement as ind collector^{- 1} generally increased, while as ind m^{- 2} generally decreased, with increasing collector' surface area (decreasing perimeter:area ratio). A second experiment investigated the efficiency of plastic grass, as a new type of artificial surface, in estimating settlement patterns of C. maenas megalopae, and compared it with that of hog's hair. Collectors of both types were deployed daily and intertidally in the lower Mira Estuary. Settlement showed the same pattern and intensity on both collector types. Plastic grass collectors constitute a good alternative to those of hog's hair, possessing several advantages over them.