Marine animal forests in high-energy environments after a large anthropic impact: discoveries from the Rion-Antirion Strait, Greece

The Rion–Antirion Strait (Greece, 50–100 m depth) hosts rich Marine Animal Forests (MAFs), formed by several species of anthozoans, sponges, bryozoans and tunicates. Using twelve video transects collected in 2019 and 2023 and a Regional Oceanographic Modelling System (ROMS) hydrodynamic model, we characterized the assemblages’ biological composition, geomorphology, and physical drivers. Strong bidirectional bottom currents (0.01–0.25 m/s, peaking at 0.8 m/s) funnel nutrients into the strait, resulting in the highest chlorophyll concentrations recorded between the adjacent Patras and Corinth Gulfs. Bridge construction (1998–2004) likely caused extensive habitat loss through dredging, excavation, ballast dumping, and fine-sediment remobilization. Today, pioneer taxa – such as Alcyonium spp. and Caryophylliidae spp. – form dense fields, benefiting from trophic flexibility, rapid recruitment, and tolerance to moderate turbidity. In contrast, fragile and less adaptable taxa such as Antipatharia and Pennatuloidea remain sparse and degraded, suggesting limited recovery potential under sustained disturbance. Sponges and tunicates play a key role in post-disturbance habitat structuring by providing settlement microhabitats. Our results suggest unexpected resilience of anthozoan assemblages in high-energy, non-rocky settings, while underscoring the ecosystem’s likely vulnerability to cumulative anthropogenic pressures. The absence of pre-disturbance baseline data limits the reconstruction of historical biodiversity levels, emphasizing the need for long-term monitoring to assess future impacts from coastal infrastructure development and climate change. These findings provide new insights into MAF ecosystem dynamics and inform targeted conservation strategies for vulnerable Mediterranean habitats.