Analysis of macrozoobenthic community structure after severe dystrophic crises in a mediterranean coastal lagoon
Lardicci, C.; Rossi, F.; Castelli, A. (1997). Analysis of macrozoobenthic community structure after severe dystrophic crises in a mediterranean coastal lagoon. Mar. Pollut. Bull. 34(7): 536-547
The macrozoobenthic assemblages of the Orbetello lagoon was studied in 1994. This basin, one of the widest western Mediterranean lagoons, showed, at the end of 1970s, very rich and highly structured communities, mainly due to the heterogeneity of its habitats and also presented large prairies of marine phanerogams. An increase in organic pollution over recent years has progressively brought about change in the environment, eventually leading in 1992 and 1993 to extended spring macrophyte blooms followed by severe dystrophic crises with high fish mortality in most of the lagoon. The aim of this study was to describe the zoobenthic community structure after these crises in order to assess the ecological conditions of the lagoon. A total of 70 species and 15332 individuals were collected at the 9 stations sampled quarterly (March, June, September, December). The results of ordination and correlation analysis indicated that the oxygen level and organic matter percentage in the sediment mainly influenced horizontal species distribution in the different sites at each sampling date. Furthermore, a clear impoverishment of the communities in comparison to previous researches was also observed. Species reduction affected not only marine taxa but also the so-called opportunistic species (primarily annelids) which were confined near sea inlets. Such patterns, which were quite unusual and differed from those described in other brackish environments with high organic pollution, gave evidence of a reduced resilience of the community despite a moderate recovery in December. The Orbetello lagoon in 1994 was therefore to be considered as under severe environmental stress and it was difficult to assess when or whether these drastic changes will be reversible.
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