Annual cycle and ecological interactions of macroalgal epiphytes with Cymodocea nodosa and Ruppia maritima in Epanomi and Vravrona, Greece

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Cymodocea nodosa and Ruppia maritima constitute key seagrasses that provide habitat, stabilize sediment, and support nutrient cycling and carbon sequestration in coastal ecosystems. This study aims to investigate the composition and abundance of epiphytic macroalgae on C. nodosa and R. maritima at the coastal sites of Epanomi and Vravrona, parts of Natura 2000 network in Greece. Seasonal plant material collection was conducted from 2022 to 2023 and epiphytic macroalgae were removed and identified to species or genera level. The coverage and number of epiphytic macroalgal taxa were determined and species were classified into Ecological Status Groups (ESGs). The similarity of macroalgal composition and coverage between seasons, locations and hosts was analyzed using cluster analysis. Vravrona exhibited higher epiphyte coverage compared to Epanomi, while Rhodophyta dominated qualitatively and quantitatively throughout the year. In Epanomi, seasonal shifts in dominance were observed, with different algal groups prevailing in each season. Cluster analysis revealed distinct clusters of epiphyte communities, indicating significant differences between sites and seasons, suggesting that local environmental conditions play a role in determining the composition and structure of epiphytic communities. The findings underscore the need for continuous environmental assessments to protect coastal waters and support conservation strategies for these critical ecosystems.