Mesophotic animal forests of the Aegean Sea support fish diversity hotspots under high fishing pressure

Abstract Marine animal forests (MAFs) are dense aggregations of habitat‐forming species that constitute essential habitats for diverse taxa including fish. However, the study of MAFs and their associated fauna remains largely skewed to their shallowest occurrence, above 30 m depth. Using closed‐circuit rebreather diving, we describe fish communities associated with newly discovered mesophotic forests of black corals ( Antipathella subpinnata ) and red gorgonians ( Paramuricea clavata ) occurring between 50 and 90 m at two sites in the Aegean Sea, Eastern Mediterranean. Mesophotic forests supported higher abundance and species richness of fish than surrounding mesophotic barrens at both sites. Fish communities associated with mesophotic forests were taxonomically and ecologically distinct from those found on shallow reefs and on mesophotic barrens. Mesophotic forests were dominated by demersal, medium‐sized species forming small schools while mesophotic barrens were dominated by small pelagic species forming large schools. Abundance and species composition of cryptobenthic fishes collected differed between depth and site but were not sensitive to the presence of mesophotic forests. Nonindigenous fish species were only observed on shallow reefs, suggesting that mesophotic depths could be less exposed to thermophilic invasions. However, mesophotic forests featured the highest densities of derelict fishing lines among all habitats surveyed, suggesting high levels of fishing pressure in surrounding areas. Given the rarity and fragility of mesophotic forests, the unique fauna they support, and their high exposure to fishing pressures, our results call for dedicated management and conservation of these ecosystems to mitigate ongoing threats to their ecological integrity.