Spatial and depth-related variation in the less-mobile vagile crustacean associates of <i>Posidonia oceanica</i> (L.) Delile in seagrass meadows on the Turkish coast of the Aegean Sea

Abstract We conducted quantitative and qualitative sampling of the less-mobile (vagile) crustaceans associated with Posidonia oceanica (L.) Delile in seagrass meadows in the Turkish Aegean Sea. We sampled 29 stations that revealed more than 35,000 individuals of 199 species belonging to seven orders, 73 families, and 119 genera of crustaceans including eight species recorded for the first time on the Turkish Aegean coast. Two introduced species, Ampithoe bizseli Özaydinli &amp; Coleman, 2012 (Amphipoda) and Processa macrodactyla Holthuis, 1952 (Caridea), and one wood-boring species of Limnoria Leach, 1814 (Isopoda) were collected. Amphipods, isopods and decapods were the most dominant groups at all depth ranges. Amphipods were the most abundant group at 0–5 m, tanaids at 6–15 m, with Chondrochelia savignyi (Kroyer, 1842) the most common species. Multivariate analyses detected significant regional structuring, with four main station clusters emerging characterized by a few widespread amphipod taxa. No significant correlations were observed between physicochemical variables and community descriptors. Results demonstrate high crustacean diversity, clear spatial structuring, and emerging ecological pressures, emphasizing the need for targeted monitoring and proactive conservation to safeguard the ecological integrity of P. oceanica meadows.