Longitudinal distribution and lateral pattern of megalopal settlement and juvenile recruitment of Carcinus maenas (L.) (Brachyura, Portunidae) in the Mira River Estuary, Portugal

Settlement is a critical process in the life history of crabs, and thus affecting the abundance, distribution and structure of estuarine communities. The spatial pattern of settlement of megalopae of the shore crab Carcinus maenas along a longitudinal estuarine gradient (Mira River Estuary, Portugal) was examined, as well as its effects on the juvenile population. To measure megalopal settlement, four replicate collectors were deployed in six equally spaced stations along the estuarine axis. Juveniles were collected on the same locations with a quadrat randomly deployed on the substrate. To assess fine-scale megalopal settlement within a curved region of the estuary, replicate collectors were deployed on both margins along Moinho da Asneira curve. Megalopae settled differently along the six longitudinal points, with a tendency to attenuate their settlement upstream. Within the curved region, megalopae preferentially settled on the left margin collectors, probably due to the weaker velocity speeds felt on this margin. Concerning the overall juvenile density, there were significant differences among the stations distributed along the estuary, but they did no reflect a longitudinal dispersion attenuation pattern. Size-frequency distribution of the juvenile population showed that the average size is higher on the left margin. Recruits (carapace length between 1.0 mm and 3.4 mm) were more abundant on the upstream stations. Density of early juveniles (3.4 mm-6.5 mm) and juveniles (6.5 mm-10 mm) was more stable throughout the estuary axis than that of recruits. This distribution pattern may result from tidal excursion processes or mechanisms to avoid biotic interactions, such as predation and competition. (c) 2006 Elsevier Ltd. All rights reserved.

Evaluation of solid residues removed from a mangrove swamp in the Sao Vicente Estuary, SP, Brazil

Mangrove swamps are found in estuaries along the coastal plains of tropical regions and have be subjected to heavy occupation and use pressure due to their privileged locations and abundance of biological resources. The present work evaluated the ecological characteristics and solid wastes accumulated in eight areas along the Santos - Sao Vicente Estuary Complex. The superficially deposited residues at each sampling site were collected and subsequently washed, drained, counted, weighed and separated into classes according to their composition and predominant use. The predominant litter type in terms of density was plastic (62.81%) and, by weight, wood (55.53%). The greatest deposition of residues was associated with areas that were less inclined and that had low plant density levels, indicating that the presence of obstacles was not critical for retaining floating residues in mangrove areas. The presence of the most frequently encountered types of solid waste residues could be explained by local activities. (C) 2010 Elsevier Ltd. All rights reserved.