Modelling distribution patterns and habitat preference of the invasive green alga Caulerpa racemosa in the Saronikos Gulf (Eastern Mediterranean)

Although the invasive alga Caulerpa racemosa has exhibited an excessive rate of prolif- eration and has invaded the entire Mediterranean Sea basin within the last 18 yr, its spatial distribu- tion patterns remain largely unknown. A 2-component modelling approach based on generalized additive models was applied to model the density of C. racemosa fronds in relation to spatial and environmental variables. A bimodal distribution of presence probability in relation to depth was observed, with higher probabilities of occurrence at very shallow bottoms (<4 m) and at depths between ~15 and 30 m. Presence probability steadily decreased at greater depths. Frond density was markedly higher in rocky habitats than in Posidonia oceanica beds or on sandy/muddy bottoms. The highest frond densities were observed in the southeastern part of the Saronikos Gulf, which is con- sidered to be the area of initial establishment of the species in the Gulf; this indicates that time favours the steady expansion and further dominance of this species.