Community structure of benthic macroinvertebrates inhabiting a highly stratified Mediterranean estuary

Abstract

SUMMARY:The community composition and spatial distribution of benthic macroinvertebrates were studied along the Ebro estuary, a highly stratified estuary located in the NE Iberian Peninsula. During the last decade the oligotrophication process occurring in the lower Ebro River and its estuary has allowed a complex benthic macroinvertebrate community to become established; these results contrast with the poor community found there in the early nineties. A total of 214 taxa were identified, and polychaetes dominated the community both in abundance and species richness. The results showed spatial differences in the structure and composition of macroinvertebrates, which suggests that there are two distinct communities along the estuary. Each community was found in a specific stretch (upper and lower estuary) in function of the presence of the salt wedge. The macrobenthos of the upper estuary was dominated by freshwater taxa, but some euryhaline species were also found. The lower estuary showed a marine community typical of shallow Mediterranean environments. The transition between these two communities fits an ecotone model. The highest abundances, richness and diversities were recorded at the lower estuarine stations, especially those closer to the river mouth, whereas the lowest values corresponded to the stations adjacent to the tip of the salt wedge.Keywords: benthic macroinvertebrates, community structure, distribution patterns, salt wedge, highly stratified estuary, Ebro estuary. RESUMEN: Estructura de la comunidad de macroinvertebrados bentónicos en un estuario mediterráneo altamente estratificado. -La composición de la comunidad y la distribución espacial de los macroinvertebrados bentónicos ha sido estudiada a lo largo del estuario del Río Ebro, un estuario altamente estratificado localizado al NE de la Península Ibérica. El proceso de oligotrofización ocurrido durante la última década en el tramo bajo del río Ebro y su estuario, ha permitido el establecimiento de una compleja comunidad de macroinvertebrados, contrastando con la comunidad encontrada a principios de los noventa. Un total de 214 taxones fueron identificados; los poliquetos constituyeron el grupo dominante en términos de riqueza y abundancia. Los resultados mostraron diferencias espaciales en la estructura y composición de macroinvertebrados, sugiriendo la existencia de dos comunidades diferentes a lo largo del estuario. Cada una de estas comunidades fue encontrada en un tramo específico (alto y bajo estuario) en función de la presencia de la cuña salina. El macrobentos del tramo alto del estuario estaba integrado mayoritariamente por taxones de agua dulce y algunos taxones eurihalinos. Por el contario, el tramo bajo presentó una comunidad marina típica de ambientes mediterráneos someros. La transición entre estas dos comunidades encajó con un modelo ecotonal. Las abundancias, riquezas y diversidades más elevadas fueron registradas en las estaciones del tramo bajo, especialmente en aquellas cercanas a la desembocadura; en cambio, los valores m...

Polychaetes of Greece: an updated and annotated checklist

“…Few records from the Mediterranean outside Greece (e.g. Spain: Nebra et al 2011; France: Guérin and Massé 1976) otherwise known from the European Atlantic coasts. Arvanitidis (1994) regards its presence in the Mediterranean as doubtful.…”

Impact of a reservoir system on benthic macroinvertebrate and diatom communities of a large Mediterranean river (lower Ebro river, Catalonia, Spain)

“…The lower part is regulated by a system of three reservoirs (Mequinensa, Riba-roja and Flix) which heavily modified the river hydrology, geomorphology and ecology by altering the magnitude, the timing and duration of flows, the sediment dynamics, the water temperature regime and the geochemistry (Ibáñez et al, 1996). In the Ebro River, benthic communities have been used to analyze the effects of chemical pollution, flow regulation and eutrophication (Cid et al, 2010;Muñoz & Prat, 1996;Tornés et al, 2007) and to assess the ecological status of the river (Oscoz et al, 2007), but in the lower Ebro most of the ecological studies have focused on the estuary area (Nebra et al, 2011;Rovira et al, 2009;Rovira et al, 2012a;Rovira et al, 2012b).…”