Seasonal Dynamics of Macroinvertebrate Communities in Offshore Mussel Aquaculture in the Southern Black Sea: Implications for Diversity

This study investigates the taxon composition, seasonal variations, and diversity dynamics of macroinvertebrate communities associated with <i>Mytilus galloprovincialis</i> cultivated in mussel longline systems in the central Black Sea. Monthly sampling conducted between September 2023 and August 2024 yielded a total of 99,719 individuals representing 20 taxa. The communities were predominantly dominated by amphipods, particularly <i>Jassa marmorata</i> (71%) and <i>Stenothoe monoculoides</i> (28%). Individual abundance peaked in autumn, whereas taxon richness reached its highest levels in summer. ANOVA results revealed significant seasonal differences in diversity indices (<i>p</i> < 0.05). Multivariate analyses, including NMDS and RDA (PCA proxy), indicated distinct seasonal clustering, with pH (41%) and salinity (35 g/kg) identified as the primary environmental drivers of community composition. These findings demonstrate that offshore mussel longline systems function not only as aquaculture infrastructure but also as reef-like artificial habitats that support benthic diversity. The dominance of opportunistic and detritivorous amphipods, along with their sensitivity to environmental gradients, suggests their potential utility as bioindicators for ecological monitoring.