Midlittoral Soft Substratum Macrofaunal Assemblages in the North Aegean Sea

Abstract. The soft substratum macrobenthic assemblages of the midlittoral zone, along the atidal shores of the upper Thermaikos (polluted) and Strymonikos (unpolluted) Gulfs in the North Aegean Sea, arc qualitatively and quantitatively described. The composition of each of the seven assemblages found (four in Thermaikos and three in Strymonikos Gulf) is statistically tested and discussed in relation to abiotic factors. One of the four Thermaikos Gulf assemblages is located on a silt to fine sand substrate in brackish waters and is characterized by the dominance of the polychactc Hedisie diversicolor and the amphipod Corophium orientate. The other three assemblages arc located on coarse substrates and characterized by the very high dominance of the bivalve Donacillu corneu and the polychactc Ophelia bicornis (both of which are exclusive inhabitants of the midlittoral zone); the First is additionally characterized by the very high dominance of the polychactc Nerine cirratulus , both the second and the third by the dominance of turbellarians due to the pollution of the Gulf (stations located near sewage discharge, high organic carbon, low oxygen). In Strymonikos Gulf, one of the three assemblages is dominated by H. diversicolor and C. orientate; it is similar to the corresponding assemblage found in Thermaikos Gulf, although located on a relatively coarSér sediment. The second is dominated by D. cornea and O. bicornis and is also similar to that of Thermaikos Gulf. The third assemblage does not have a corresponding one in Thermaikos Gulf, is located on a substrate consisting of granules to pebbles, arid is characterized by the high dominance of the amphipods Allorchestes aquilinus and Echinogammarus olivii and the isopod Sphaeroma Sérratum. The corresponding assemblages of the two gulfs are compared. The results of the data analysis are discussed and compared with the literature.