The macrozoobenthic community structure and dynamics at low salinities (0.3 -6 psu) in a Mediterranean lagoon (Monolimni lagoon) were investigated. Samples were collected monthly from February 1998 to February 1999 at two sampling stations. Community structure was analyzed by means of uniand multivariate methods. 21 taxa were collected; the amphipod Corophium orientale and the gastropod Ventrosia maritima dominated the assemblages. Total abundance peaked (50,000 -60,000 individuals m -2 ) in mid or late autumn. Community structure showed an almost even seasonal periodicity; seasonal changes were mainly derived from the intense variation in abundance of most species and the non-occurrence of a few ones (e.g. Corophium insidiosum, Polydora ciliata) in spring and summer. Nonoccurrence, which led to a depression of the most diversity indices, was possibly the only direct impact of the extremely low salinities (~0.3 psu) on community structure. The main structuring factors of the community in the deeper outer part of the lagoon were water temperature and depth, and in the innermost part, where a Ruppia maritima meadow occurred, were water temperature and predation pressure by crabs (Carcinus aestuarii) and gobies (Knipowitchia caucasica). A temporary decline in total abundance in summer followed an increase in abundance of these predators.
IntroductionCoastal brackish habitats have been the subject of extensive studies. Nevertheless, the factors determining the pattern of distribution and seasonal dynamics of the macrobenthic fauna in these habitats are not yet sufficiently known. GUELORGET and PERTHUISOT (1992) introduced the concept of "paralic ecosystem" and "confinement" and applied these concepts mainly to the study of the coastal brackish habitats of the microtidal Mediterranean Sea. The authors proposed that "confinement", which represents the turnover time of marine water, is the main factor determining the horizontal zonation of benthic assemblages in the coastal brackish ecosystems ("paralic" ecosystems); they also stated that the populations in these ecosystems remain stable despite frequent considerable environmental variations (e.g. in salinity); even more, summer dystrophic crises do not destroy the ecosystem which recovers quickly once the crisis is over.Useful information on the seasonal dynamics of the macrozoobenthic assemblages in Mediterranean coastal brackish habitats was given in some mainly recent publications (e.g. REIZOPOULOU et al., 1996;LARDICCI et al., 1997;TAGLIAPIETRA et al., 1998;KOUTSOUBAS et al., 2000); several of these studies were carried out in lagoons, which suffer from summer dystrophic crises. However, the monthly variation in macrobenthic community structure and the associated environmental factors at very low salinities in Mediterranean brackish habitats have not substantially been investigated. Monolimni lagoon, which is located in the Evros Delta (Northern Aegean), is a poikilohaline, relatively enclosed Mediterranean brackish system. Although a significant scientific...
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