Epibenthic Invertebrate Diversity on Sublittoral Rocky Habitats in Marine Protected Areas of the North Aegean Sea After a Severe Heatwave Event

Marine invertebrates, such as sponges, corals, mollusks and sea squirts, are appropriate climate-change descriptors on sublittoral rocks. The present study assesses the diversity, relative abundance and health condition of epibenthic invertebrates inhabiting sublittoral rocky habitats within the Natura 2000 network (Chalkidiki, north Aegean), after the 2021 marine heatwaves. Samplings were made with non-destructive techniques in autumn 2021 by diving along vertical belt transects (up to 30 m). Fourteen stations were surveyed, revealing 56 macroscopic invertebrates, 16 algae and 15 reef-associated fishes. Richness showed increased values at the deepest and steepest cliffs. Reefs were the dominant habitat type, hosting different facies of infralittoral algae and coralligenous biocenoses. Three algal (Halimeda tuna, Peyssonelia squamaria, Lithophyllum strictiforme) and 12 invertebrate (Aplysina aerophoba, Chondrilla nucula, Chondrosia reniformis, Ircinia variabilis, I. oros, Sarcotragus foetidus, Spongia officinalis, Balanophyllia europaea, Cladocora caespitosa, Pinna nobilis, Spondylus gaederopus, Microcosmus sabatieri) species were found in partial or full necrosis. According to relevant data collected about 20 years ago, the biota had higher diversity without signs of necrosis. Sarcotragus foetidus, I. variabilis, B. europaea, C. caespitosa and S. gaederopus were the most affected by necrosis species over the surveyed area. They represent appropriate climate change descriptors to assess the resilience of Mediterranean MPAs, being priority species in marine conservation.