A study of the benthic community structure of Demospongiae (Porifera) in Kalloni gulf at Lesvos Island (NE Aegean Sea, Greece)

Abstract Kalloni gulf at Lesvos Island in Aegean Archipelagos is an ecosystem where, despite its small size and the poor availability of suitable substrate, macrobenthic invertebrates find a living environment that fosters the development and growth of their populations. Among these invertebrates the Demospongiae stand out with 54 different species. In this paper the structure of demosponge communities is described according to the different types of inorganic and organic substrata encountered in Kalloni gulf. The data used for this study cover a comprehensive period of ten years. Competitiveness in finding the appropriate substrate in the limited space of the gulf is an important factor, not only among individuals of the same taxon, but also among different species, explaining the considerably high proportion of sponges that live as epiphytic and epizoic organisms. During sampling outside of typical inorganic substrata, 18 species of sponges or 33.3% of total identified species were epiphytic and 31 or 57.4% of the species encountered were epizoic. 14 species or 26% demonstrated the ability to survive both as epizoic and epiphytic. Cluster analysis and taxonomic distinctness indices ( Δ + and Λ + ) analysis demonstrated that the colonization of different substrata, inorganic and organic by demosponges is rather non-specific, due to the limited substrate available.