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

Publicado

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

Publicado

[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

Hábitos alimentarios de tres especies de raya (Rajiformes: Urotrygonidae) en el Pacífico central mexicano

Se realizó el análisis del contenido estomacal y de las interacciones tróficas de tres especies de raya (Urobatis halleri, Urotrygon munda y Urotrygon rogersi) capturadas en la plataforma continental del Pacífico central mexicano durante los dos periodos hidroclimáticos (T1 y T2) que caracterizan la variabilidad ambiental en la zona. Las tres especies de raya presentaron un estrecho intervalo de distribución batimétrica, y su máxima abundancia se presentó a los 20 m en ambos periodos de estudio. En general, las dietas estuvieron compuestas principalmente de microcrustáceos bentónicos (camarones carídeos) y en menor proporción de peces, poliquetos y moluscos. Las categorías de presas de mayor abundancia en las dietas fueron los carídeos de las familias Processidae y Ogyriididae, y peneidos, y en segundo término las larvas de braquiuros y estomatópodos. La estrategia alimentaria exhibida por las tres especies fue generalista. Las dietas mostraron valores altos de superposición durante el periodo T1 tanto en el análisis de intra como de interespecies, mientras que durante el periodo T2 la superposición de las dietas fue menor. No se evidenciaron cambios ontogénicos en las dietas, y el sexo tampoco representó un factor de diferencias tróficas. Se considera que las ligeras diferencias en las dietas son debidas a los cambios estacionales en las asociaciones de macroinvertebrados de fondos blandos de la zona somera, y que las relaciones como competencia y depredación no son los factores más determinantes en la dinámica de las tres especies de raya analizadas

Feeding habits of three round stingrays (Rajiformes: Urotrygonidae) in the central Mexican Pacific

Stomach contents and dietary overlap of three round stingray species (Urobatis halleri, Urotrygon munda, and Urotrygon rogersi) captured off the central Pacific coast of Mexico were analyzed during the two main hydroclimatic periods (T1 and T2) that characterize the environmental variability in the area. The three round stingray species showed a narrow bathymetric distribution range, and the highest abundances were located at 20 m depth in both seasons. In general, the diets were mainly composed of benthic microcrustaceans (caridean shrimps) and to a lesser extent of fishes, polychaetes, and molluscs. The most abundant prey items in the diets were carideans of the families Processidae and Ogyriididae, and penaeids, followed by brachyuran and stomatopod larvae. All three stingrays exhibited a generalist feeding strategy. The diets showed high overlap values during period T1 in both inter- and intraspecies analyses, but lower values during period T2. There was no evidence of ontogenetic diet changes and sex was not a factor for trophic differences. The slight differences among diets were due to seasonal changes in the soft-bottom macrobenthic invertebrate assemblages in the shallow waters, and relationships like predation and competition were not the main factors influencing the population dynamics of the three stingray species.