The Use of Artificial Benthic Collectors for Assessment of Spatial Patterns of Settlement of Megalopae of Carcinus maenas (L.) (Brachyura: Portunidae) in the Lower Mira Estuary, Portugal

Abstract

Artificial benthic collectors have been widely used for the assessment of settlement rates of decapod crustaceans. However, to date no consistent works have addressed spatial patterns of settlement in different estuarine habitats, and no specific studies targeted the interaction of artificial surfaces with the surrounding natural substrate. It may be expected that the artificial surface may produce a different thigmotactic response when compared to the natural substrate, which may limit the use of this technique for assessment of natural settlement rates. In this study the settlement rates of megalopae of the estuarine crab Carcinus maenas were addressed, specifically deploying artificial benthic collectors in different habitats both intertidal and subtidal in the lower Mira estuary. A number of experiments were performed concerning stratification and temporal fluctuations of settlement. Further, the interaction of collector surface with the surrounding substrate was investigated, by comparing settlement rates in natural and artificial substrates in different habitats. Results have shown significant differences in settlement between different estuarine habitats, both in spatially replicated experiments and in a high-resolution temporal experiment. However, comparison between settlement rates in artificial and natural substrates has shown that there is a strong interference between collectors and surrounding substrate, limiting interpretation of results concerning settlement rates in artificial substrate alone.

Cannibalism, post-settlement growth rate and size refuge in a recruitment-limited population of the shore crab Carcinus maenas

“…In agreement to early studies on the ecology of juvenile stages of the green shore crab, our results confirm that population size is partially regulated by the availability of structural complex habitats. Megalopae and first instar juveniles exhibit high plasticity in selecting habitats and exploring refuges among several heterogeneous substrates (Almeida ad Queiroga, 2003;Hedvall et al, 1998;Moksnes et al, 2003;Paula et al, 2006), and structured habitats are selected mainly because they provide shelter that prevents predation (Hedvall et al, 1998;Moksnes et al, 2003) and concentrate living and dead organic matter that may be used as food (Perkins-Visser et al, 1996). We report a nearly absence of crabs in sandy substrates, but in our study system dense vegetation cover not always sustained larger crab densities.…”

Bromine soil/sediment enrichment in tidal salt marshes as a potential indicator of climate changes driven by solar activity: New insights from W coast Portuguese estuaries

“…Finally, the vertically well-mixed Mira estuary (4.5 km 2 ) is a narrow incised estuary oriented NE-SW (e.g., Paula et al, 2006). It presents a semi-diurnal mesotidal regime with a mean tidal range of about 2.4 m and a HHWS of 3.5 m (Amaral et al, 2007).…”

A comparative analysis of benthic nematode assemblages from Zostera noltii beds before and after a major vegetation collapse

“…Upstream tidal penetration is generally limited by the region's annual rainfall distribution concentrated between January and March, with the rest of the year being usually dry. In addition, the annual rainfall has a clear influence on the changes of sedimentation dynamics (Paula et al, 2006). Due to the low, seasonal and limited freshwater input, the lower section of the estuary has a dominant marine signature, and was characterised until 2008 by extensive, homogeneous Z. noltii meadows mainly in the intertidal area, with a strong seasonality and high biomass in the warm months.…”