The Strait of Sicily is an hydrodynamically active stretch of sea in the centre of the Mediterranean Sea, crucial for its circulation, as waters masses from the western basin meet water masses of the eastern one. In this context, zooplankton represents an excellent indicator of the ecology of pelagic environment of the area. The aim of this study is to describe the general composition and distribution of the zooplanktonic community sampled during summer 2025 with the “OurOBS 2025” scientific survey.

The samples were collected in 32 stations located between Malta and the southern coast of Sicily (GSAs 15 and 16) using a Bongo 40 equipped with 200 µm mesh sized net. In each sampling station, environmental factors were recorded with a CTD probe. In the laboratory, sorting of larger organisms and taxonomical analysis were carried out, as well as the counting of the smaller organisms (e. g. copepods, cladocerans, gastropods larvae), and then density of individuals/m³ was calculated. A total of 133 organisms were identified to the lowest taxonomical level possible. Multivariate analyses reveals that the community composition is coherent with the summer circulation models in the area, as the species composition of each sampling point resulted in a clustering driven by the water column stability (Brunt–Väisälä frequency) with statistical significance. SIMPER analysis revealed that cluster dissimilarity is tied almost totally to the abundance of copepods, appendicularians and teleost eggs.

These preliminary results help to improve the understanding of the structure of zooplankton communities in the central Mediterranean Sea and provides a basis for future studies focusing on ecological monitoring, on the introduction of alien species and the assessment of plankton responses to climate change.