Unveiling the diversity of benthic habitats of the Romanian Black Sea coast: New records and an updated checklist

This study presents a comprehensive ecological assessment of the benthic habitats along the Romanian Black Sea coast, with a central focus on the rediscovery and population analysis of the rare burrowing bivalve Barnea candida. Reported for the first time in over six decades, the species was identified in marl soft-rock outcrops stations at two stations located in shallow areas, making it a significant conservation milestone. Detailed morphometric measurements were used to evaluate population structure and growth patterns. Our results revealed the presence of both mature and juvenile individuals, indicating successful local recruitment and habitat resilience. Thirteen stations corresponding to distinct benthic habitats (marl outcrops, biogenic reefs, photophilic algae beds, seagrass meadows, and deep rock substrata) have been analyzed in terms of species richness and community structure using both density and biomass data and integrated with substrate. The faunal associations included Brachynotus sexdentatus and Pholas dactylus with marl beds, Molgula manhattensis on shallow rock with photophilic algae, Mytilus and Mytilaster on exposed biogenic reefs, and Petricola lithophaga in deep rocky areas. A new record of Zostera marina and the reappearance of the red alga Dasya pedicellata were also documented, further highlighting the ecological value and recovery potential of these coastal systems. Overall, this study provides the first integrated ecological and population-level analysis of Barnea candida in the region, highlighting marl beds as keystone microhabitats for its conservation. The findings aim to support monitoring, habitat protection, and benthic biodiversity management in the Romanian Black Sea coastal waters.