Influence of environmental factors on the dynamics of macrobenthic crustaceans on soft-bottoms of the Ebro Delta continental shelf (northwestern Mediterranean)

Abstract

SUMMARY: Short-term temporal variability in infaunal crustacean communities was evaluated against environmental variability. The area of study was located at two stations at 45 and 60 m depth under the influence of the Ebro River. Differences in the relative abundance of crustacean species between sites might be related to the distance from the river, with higher organic matter supply and finer mud content near the river. There was a marked seasonal variability linked to high phytoplankton production in spring, which supplied organic matter to the benthos, inducing higher crustacean abundance. In late summer there was a reduction in the infaunal crustacean abundance and species richness that could have been caused by two factors: the establishment of the thermocline, which could limit the availability of organic matter to the seabed, and the high water temperatures, which caused the production of phytoplankton exudates and accumulation of mucilaginous aggregates over the seabed. The 45-m site was under the influence of otter-trawl fishing and precisely in this area the seasonal variability was not observed, probably masked by the effects of trawling impact.Keywords: Peracarida, benthos, spatial variations, muddy sediments, temperature, mucilaginous aggregates. RESUMEN: Influencia de factores ambientales en la dinámica de crustáceos macrobentónicos en fondos fangosos de la plataforma continental del Delta del Ebro (Mediterráneo noroccidental). -Evaluamos la variabilidad temporal de la comunidad de crustáceos endobentónicos frente a la variabilidad ambiental a pequeña escala. El estudio se sitúa en la plataforma continental frente a la desembocadura del Rio Ebro, en dos estaciones de muestreo a 45 y 60 m de profundidad. Las diferencias en la abundancia relativa de crustáceos entre las dos estaciones pueden estar relacionadas con la distancia a la desembocadura del Ebro, con un mayor aporte de materia orgánica y mayor contenido de fango cerca del rio. Observamos una variabilidad estacional relacionada con la alta producción de fitoplancton en primavera, con aportes de materia orgánica al bentos favoreciendo una mayor abundancia de crustáceos. Al final del verano se establece la termoclina, pudiendo limitar el aporte de materia orgánica al bentos, y junto con las altas temperaturas, que originaron acumulaciones de exudados de fitoplancton en el fondo, pudo causar una reducción en la abundancia y riqueza específica. La variabilidad estacional no es tan marcada en la estación de muestreo a 45 m. Esta zona está impactada por la pesca de arrastre, que probablemente enmascara la variabilidad temporal.

Decapod crustaceans associated with an artificial reef (Adriatic Sea)

“…The decapod crustaceans represent one of the most dominant and diversified group of infaunal communities, constituting a key taxon linking lower and higher trophic levels (Wenner & Boesch, 1979;Cartes, 1998;Fanelli et al, 2007) and having a variety of ecological functions (De Juan & Cartes, 2011). They include organisms with varied feeding behaviour (e.g.…”