The biological features, population dynamics and secondary production of Carcinus maenas were studied between June 2003 and June 2004 in four areas within the Mondego estuary, Portugal. Benthic samples were collected monthly, during the night, at high water of spring tides using a 2-m beam trawl, and plankton samples were collected monthly, during the day, at high tide with a Bongo net. Only the first zoeae stage of C. maenas larvae was found in the plankton; it was collected at all sampling stations throughout the year. A continuous pattern of benthic recruitment was observed in the upstream areas of the estuary with the highest peaks occurring in the spring 2004. Females carrying eggs were also caught through the year, although mainly in downstream areas. Juveniles' sex-ratio was favourable to males at almost all the sites sampled. Ventral carapace colour varied between green and orange-red, with the proportion of the green morphotype increasing with the increasing distance from the mouth of the estuary. The proportion of crabs in moult also increased from downstream to upstream areas. For both sexes the crab population showed a similar size structure throughout the year. The upstream areas of the estuary were characterized by the dominance of juveniles, with adults migrating to downstream areas. The average annual production of C. maenas, P (growth production), was estimated at 0.08 g m ÿ2 y ÿ1 AFDW, and the average annual biomass (B) was estimated at 0.058 g m ÿ2 , resulting in a P=B ratio of 1.4.
This study investigated the extent to which the plasticity of a generalist, opportunistic species allows individuals to shift their feeding ecology and foraging niche, throughout the annual cycle, and between 2 years of contrasting diet and oceanographic conditions during the breeding season. The spatio-temporal variations in the foraging niche of an overpopulated gull species -the yellow-legged gull Larus michahellis population at Berlenga Island (Portugal)were assessed using blood (plasma and cells) and different feathers for stable isotope analyses (δ 13 C and δ 15 N) from 52 breeding adults in 2 consecutive years (2011 and 2012). In addition, GPS loggers were deployed on 11 individuals (and removed after several foraging trips) to infer the foraging behaviour of this species during the incubation period. Results suggest inter-annual differences in the feeding ecology and foraging behaviour of birds during the breeding season that were associated with the availability of food resources around the colony. Despite the high feeding plasticity and opportunistic behaviour of yellow-legged gulls, individual birds exhibited shortand long-term consistency in their feeding ecology, with exception of the period between winter and pre-laying. Our results support the hypothesis that individual feeding preferences throughout most of the annual cycle are an intrinsic characteristic of this population, and potentially of related opportunistic and generalist species.
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