Dynamics of the small-scale spatial structure of a population of the spider crab maja brachydactyla (Decapoda: Majidae)

Spider crab (Maja brachydactyla) juveniles inhabit shallow coastal areas until they reach maturity and start a mating migration toward deeper waters. Small-scale spatial distribution was analyzed for a shallow-water local population using data from a monthly trap sampling study conducted from December 1997 to November 1999. The trap arrangement formed a grid covering a total area of 3.2 km2. Catch per unit of effort (CPUE) for each biological category (defined by sex and maturity status) was modeled using geostatistics to analyze the spatial structure and to map distribution. Juveniles showed persistent aggregations roughly 150300 m in diameter and no large-scale movements. Juvenile patches were highly stable in time. During summer, some of the juveniles attained sexual maturity and the aggregation broke up. It was reestablished in September and October, when new juveniles recruited. Adults found in shallow waters did not show a clear spatial structure. The relation variance per mean CPUE was used as a dispersion index (DI). Juveniles were highly aggregated (DI > 1) throughout the whole year, except during the period when the terminal molt took place. Adults were almost randomly distributed (DI ≈ 01). In the case of juveniles, the DI was significantly and positively correlated with CPUE, and was negatively correlated with size, but did not show any significant correlation either with the percentage of individuals undergoing molt or with temperature

Distribution and habitat use patterns of benthic decapod crustaceans in shallow waters: A comparative approach

Coastal areas are widely considered to be nurseries for many marine species. New approaches to this concept take into account interactions among environmental variables and ecological variation related to geographical location, as well as the complex life cycles of marine invertebrates. We present a comparative approach to assessing the association between environmental variables and patterns of distribution and the habitat use of benthic decapod species in coastal areas. Through this approach we infer which processes underlie these patterns and identify appropriate habitat-use models. An intensive fine-grain sampling design was used to account for environmental gradients occurring at different spatial scales (defined by substrate type, depth, exposure and geographical location) in a temperate oceanic bay (Ria de A Coru�a, NW Spain). A high proportion of juveniles occurred in most populations, but our results did not allow us to generally designate coastal areas as nurseries, except for a few species, which showed marked spatial segregation between juveniles and adults. Coastal habitats are predominantly used as nurseries by juveniles of larger species, while, for smaller decapods, they seem to constitute habitats for the entire population. Larval transport may account for mesoscale distribution patterns, while microscale distribution may respond to the complex interaction among different processes, i.e. habitat selection at settlement, differential mortality among habitats, post-settlement dispersal and ontogenetic habitat shifts. Sandy substrates were characterised by low-diversity communities dominated by hermit crabs. In rocky bottom communities, variability in spatial patterns was mostly related to substrate type and geographical location. Caridean shrimps had higher densities on flat rock surfaces, with similar juvenile and adult patterns. Anomuran species occurred mainly on cobbles. Distribution patterns of brachyurans varied among species, but did not change greatly from juveniles to adults. � Inter-Research 2006

Growth at moult, intermoult period, and moulting seasonality of the spider crab Maja brachydactyla: combining information from mark-recapture and experimental studies

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Spatial structure of the spider crab, Maja brachydactyla population: Evidence of metapopulation structure

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[Trophic interactions of the six most abundant fish species in the artisanal fishery in two bays, central Mexican Pacific]

We surveyed the trophic components in six species of Bahia de Navidad and Bahia de Chamela: Microlepidotus brevipinnis, Caranx caballus, Haemulon flaviguttatum, Lutjanus guttatus, L. argentiventris and Mulloidichthys dentatus. Two main seasonal periods were considered: 1) North Equatorial Counter Current NECC period influence (T1) and 2) California Current CC period influence (T2). In Bahia de Navidad 78 prey taxa were identified in the stomachs. From July to December (T1), 64 prey taxa were found, and from January to June (T2), 45 prey items. In Bahia de Chamela 93 prey items were identified; 74 during T1 and 60 during T2. The highest prey number was found in the stomachs of M. dentatus during T1 in Bahia de Navidad and the lowest prey number (7) was recorded in H. flaviguttatum in Bahia de Navidad in the same period. Crustaceans were the most frequently recorded prey items, followed by fishes, mollusks, polychaetes, and echinoderms in both seasonal periods and sites. The six fish species studied are considered as specialist feeders due the low values of the niche breadth index. There was little similarity among the diets

Interacciones tróficas de las seis especies de peces más abundantes en la pesquería artesanal en dos bahías del Pacífico Central Mexicano

Se analizaron los componentes tróficos de las seis especies de peces más importantes en la captura de la pesquería artesanal en las Bahía de Navidad y Chamela, ubicadas en la costa de Jalisco, México. Las especies estudiadas fueron Microlepidotus brevipinnis, Caranx caballus, Haemulon flaviguttatum, Lutjanus guttatus, Lutjanus argentiventris y Mulloidichthys dentatus. Se consideraron dos periodos de estudio de acuerdo a las pautas hidroclimáticas y los patrones de producción biológica en la zona: periodo de influencia de la Contracorriente Norecuatorial (T1), y periodo de influencia de la Corriente de California (T2). En Bahía de Navidad se identificaron 78 presas en total para las seis especies. En el periodo comprendido entre julio y diciembre (T1) se identificaron 64 presas y 45 de enero a junio (T2). En Bahía de Chamela se identificaron 93 presas, encontrando 74 presas en el periodo T1 y 60 presas para el periodo T2. El mayor número de presas se encontró en M. dentatus con 34 presas en el periodo T1 de Bahía de Chamela y el menor número fue en H. flaviguttatum en T1 de Bahía de Navidad con solo 7 presas. Los crustáceos fueron las presas de mayor presencia en la dieta, seguidos por peces, moluscos, poliquetos y equinodermos, en ambos periodos y sitios de muestreo. Las seis especies analizadas se consideran como especialistas, dados los bajos valores del índice de amplitud de nicho en ambos periodos y sitios de muestreo

[Trophic interactions of the six most abundant fish species in the artisanal fishery in two bays, central Mexican Pacific]

We surveyed the trophic components in six species of Bahia de Navidad and Bahia de Chamela: Microlepidotus brevipinnis, Caranx caballus, Haemulon flaviguttatum, Lutjanus guttatus, L. argentiventris and Mulloidichthys dentatus. Two main seasonal periods were considered: 1) North Equatorial Counter Current NECC period influence (T1) and 2) California Current CC period influence (T2). In Bahia de Navidad 78 prey taxa were identified in the stomachs. From July to December (T1), 64 prey taxa were found, and from January to June (T2), 45 prey items. In Bahia de Chamela 93 prey items were identified; 74 during T1 and 60 during T2. The highest prey number was found in the stomachs of M. dentatus during T1 in Bahia de Navidad and the lowest prey number (7) was recorded in H. flaviguttatum in Bahia de Navidad in the same period. Crustaceans were the most frequently recorded prey items, followed by fishes, mollusks, polychaetes, and echinoderms in both seasonal periods and sites. The six fish species studied are considered as specialist feeders due the low values of the niche breadth index. There was little similarity among the diets