Temporal and spatial patterns of settlement of brachyuran crab megalopae at a rocky coast in Central Portugal

Abstract

Square mesh traps placed under natural boulder cover were used to obtain in situ settlement rates of intertidal brachyurans along a rocky coast within the Cascais area, Central Portugal. Megalopae of all intertidal species known to occur in this region were present in the samples. The settlement variability within different spatial scales, i.e. hundreds, tens and unit metres, were tested for the most abundant species, Pachygrapsus marmoratus, using a nested analysis of variance design. A significant contrast was found between areas 1.5 km apart, while no differences were detected at lower spatial scales. Spatial heterogeneity is likely to depend on coastal hydrological patterns rather than smaller-scale processes such as substrate selection. Fine time series settlement data were obtained for P. marmoratus and Xantho incisus, which were analysed for periodic patterns and correspondence to tide range and wind speed components. Across-shore wind forcing was found to be the major factor affecting settlement for both species, although in inverse ways. While onshore winds favour settlement of P. marmoratus, it is the relaxation of the onshore component or contrary offshore forcing that is apparently transporting the megalopae of X. incisus ashore. We predict that the vertical distributions of X. incisus and P. marmoratus megalopae are different within the inner shelf and that wind-driven upwelling and downwelling compensating coastal flows are largely determining their temporal abundance variation. In the case of P. marmoratus, there is also a secondary but significant effect of tides on the abundance of megalopae. An increasing number of settlers on traps was verified during periods of higher tide range. This seems to be particularly marked during spring tides around the new moon, but there is no statistical support for such a trend.KEY WORDS: Settlement patterns · Rocky intertidal zone · Brachyuran crabs · Megalopae · Log-linear models Resale or republication not permitted without written consent of the publisher

Shelf and estuarine transport mechanisms affecting the supply of competent larvae in a suite of brachyuran crabs with different life histories

“…A number of studies suggest that alternative processes may better explain temporal and spatial settlement patterns. For instance, cross-shore wind components, not longshore, apparently transport late larval stages of intertidal crabs to rocky areas of the Central Portuguese coast, suggesting that larvae follow a downwind path (Flores et al 2002).…”

“…A number of studies suggest that alternative processes may better explain temporal and spatial settlement patterns. For instance, cross-shore wind components, not longshore, apparently transport late larval stages of intertidal crabs to rocky areas of the Central Portuguese coast, suggesting that larvae follow a downwind path (Flores et al 2002).Besides the transport from shelf waters to the coast, late stage larvae of estuarine species necessarily undertake upstream migration toward appropriate habitat on which to settle (Shanks 1995). For this task, most planktonic larvae of invertebrates and fish conduct vertical migrations triggered by the strong vertical shear of salinity and hydrostatic pressure of tidal currents (reviewed by Forward & Tankersley 2001).…”

Stimulation of molting in megalopae of the Asian shore crab Hemigrapsus sanguineus: physical and chemical cues

“…A commonly used method to collect crab megalopae from the plankton is to suspend fibrous collectors constructed of hemp rope or hogshair filter material in seawater (Shanks 1983, Metcalf et al 1995, Hasek & Rabalais 2001, or to place pieces of mesh on rocky shores (Flores et al 2002). This suggests that fibrous and mesh materials stimulate settlement of megalopae, but the influence of those materials on molting is unknown.…”

Asentamiento diario de megalopas de jaibas del genero Cancer en un estuario micromareal

“…(Ogburn & Forward, 2009). En otras áreas con fuertes frentes de surgencia, como la costa portuguesa, especies de braquiuros evaluados simultáneamente también muestran divergencias en su patrones de asentamiento (Flores et al, 2002). El transporte de larvas a la costa en condiciones de surgencia o relajación estaría asociado principalmente a la ubicación de las larvas de cada especie en la columna de agua (Flores et al, 2002).…”