Interannual changes in the composition of the macrobenthic fauna of Drana lagoon (Evros Delta, N. Aegean Sea): preliminary note

The qualitative and quantitative composition of macrobenthic fauna of Drana lagoon, Evros Delta, was investigated during summer of 1981, 1997 and 1998. Since 1987 Drana lagoon has been isolated from the sea due to the obstruction of its narrow opening. In September 1998, samples were collected in an emerged and in a submerged site, since the major part of the lagoon was temporarily drained due to evaporation. An alteration in the faunal composition characterized by the vanishing of marine species and an increase of the dominance of the most resistant estuarine species (Hydrobia sp., Hediste diversicolor, Gammarus aequicauda), was recorded during July 1997 in relation to September 1981. This alteration may be the result of the lagoon's isolation from the sea. Furthermore, this isolation resulted in the temporary drainage of the major part of the lagoon during September 1998, when Hydrobia sp. showed a 98 \% dominance at the submerged site and was the unique species found at the emerged one. Number of species and total density together with biomass had comparatively higher values in September 1981 and in July 1997 samples, respectively. Species diversity and evenness showed significantly lower values in September 1998 samples while evenness had significantly higher values in July 1997 samples.