Contrasting Responses to Harvesting and Environmental Drivers of Fast and Slow Life History Species

According to their main life history traits, organisms can be arranged in a continuum from fast (species with small body size, short lifespan and high fecundity) to slow (species with opposite characteristics). Life history determines the responses of organisms to natural and anthropogenic factors, as slow species are expected to be more sensitive than fast species to perturbations. Owing to their contrasting traits, cephalopods and elasmobranchs are typical examples of fast and slow strategies, respectively. We investigated the responses of these two contrasting strategies to fishing exploitation and environmental conditions (temperature, productivity and depth) using generalized additive models. Our results confirmed the foreseen contrasting responses of cephalopods and elasmobranchs to natural (environment) and anthropogenic (harvesting) influences. Even though a priori foreseen, we did expect neither the clear-cut differential responses between groups nor the homogeneous sensitivity to the same factors within the two taxonomic groups. Apart from depth, which affected both groups equally, cephalopods and elasmobranchs were exclusively affected by environmental conditions and fishing exploitation, respectively. Owing to its short, annual cycle, cephalopods do not have overlapping generations and consequently lack the buffering effects conferred by different age classes observed in multi-aged species such as elasmobranchs. We suggest that cephalopods are sensitive to short-term perturbations, such as seasonal environmental changes, because they lack this buffering effect but they are in turn not influenced by continuous, long-term moderate disturbances such as fishing because of its high population growth and turnover. The contrary would apply to elasmobranchs, whose multi-aged population structure would buffer the seasonal environmental effects, but they would display strong responses to uninterrupted harvesting due to its low population resilience. Besides providing empirical evidence to the theoretically predicted contrasting responses of cephalopods and elasmobranchs to disturbances, our results are useful for the sustainable exploitation of these resourcesVersión del editor4,411

Seasonal and interannual variability of zooplankton community in waters off Mallorca island (Balearic Sea, Western Mediterranean): 1994-1999

During 1994-1999, the mesozooplankton community was sampled monthly in the upper sea layer (up to 100 m) along a cross-shelf transect of three stations in waters off Mallorca island. Copepods formed the most abundant group (54%) followed by appendicularians (17%), cladocerans and meroplankton larvae (13%). The abundance of all these groups decreased in the offshore direction but it was not the case for other zooplankton groups. A clear seasonal cycle was evident consisting of a general decrease of the abundance from the beginning to the end of the year. In addition to the general increase during late winter and spring, an absolute maximum was detected in May, particularly important at the neritic station and a relative maximum in March and October. During this annual cycle, the community structure was almost maintained. An interannual trend was also present, characterized by an overall decrease in the total zooplankton abundance from 1994 to 1999. Concurrent measurements of water and air temperature show that this trend was correlated with a warming of coastal waters of atmospherical origin. In particular. a marked minimum in zooplankton abundance was recorded during 1998, which was the warmest year registered. During 1997-1998, the warming was also associated with the presence of fresh, nutrient-poor southern waters of Atlantic origin.De 1994 à 1999, la communauté superficielle du mésozooplancton des cent premiers mètres a été échantillonnée le long d'une radiale de trois stations au large de Majorque. Les copépodes représentent le groupe le plus abondant (54 %) suivi des appendiculaires (17 %), des cladocères et des larves de méroplancton (13 %). L'abondance de ces groupes décroît au fur et à mesure que l'on s'éloigne de la côte, ce qui n'est pas le cas pour les autres groupes de zooplancton. Le cycle saisonnier est très marqué, avec une diminution générale de l'abondance entre le début et la fin de l'année. L'augmentation pendant la première moitié de l'année est marqué par un maximum détecté au printemps, particulièrement important au niveau de la station néritique, et un maximum relatif pendant l'hiver et l'automne. Cet écart s'amoindrit cependant au large. On remarque une tendance interannuelle caractérisée par une diminution générale de l'abondance totale du zooplancton entre 1994 et 1999. Des mesures de la température de l'eau et de l'air démontrent que cette tendance est liée à un réchauffement d'origine atmosphérique des eaux du plateau continental. En 1998, l'année la plus chaude, on a enregistré un minimum important de l'abondance du zooplancton. En 1997 et 1998, les températures élevées étaient liées à la présence de masses d'eau plus chaude venue du sud, moins riches en sels nutritifs et d'origine Atlantique

Seasonal variability of copepod abundance in the Balearic region (Western Mediterranean) as an indicator of basin scale hydrological changes

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Mediterranean marine copepods: basin-scale trends of the calanoid Centropages typicus

The Mediterranean Sea is located in a crossroad of mid-latitude and subtropical climatic modes that enhance contrasting environmental conditions over both latitudinal and longitudinal ranges. Here, we show that the large-scale environmental forcing is reflected in the basin scale trends of the adult population of the calanoid copepod Centropages typicus. The species is distributed over the whole Mediterranean basin, and maximal abundances were found in the north-western basin associated to oceanic fronts, and in the Adriatic Sea associated to shallow and semi enclosed waters. The peak of main abundances of C. typicus correlates with the latitudinal temperature gradient and the highest seasonal abundances occurred in spring within the 14–18°C temperature window. Such thermal cline may define the latitudinal geographic region where C. typicus seasonally dominates the >200 μm-sized spring copepod community in the Mediterranean Sea. The approach used here is generally applicable to investigate the large-scale spatial patterns of other planktonic organisms and to identify favourable environmental windows for population developmentPublicado