Population dynamics of a temperate coral along a depth gradient in the Dardanelles

Notwithstanding the importance of analyzing the variations of population dynamic traits along environmental gradients for assessing coral resilience to global climate change, temperate areas are more understudied than tropical regions. In the Mediterranean Sea, some studies are available for its western basin, while there is a lack of information for its eastern basin. This study starts to fill this gap, by determining the demographic characteristics of the solitary zooxanthellate scleractinian Balanophyllia europaea in the Dardanelles (Turkey) along a 1–21 m depth transect. The population dynamics of B. europaea from this site in the eastern Mediterranean Sea was compared with the populations in the NW Mediterranean Sea. In particular, the sites of Calafuria and Palinuro (Tyrrhenian Sea, Italy) were chosen for the comparison since their temperature and latitude, respectively, were similar to that of the Dardanelles population. The population density in the Dardanelles increased exponentially with depth, possibly due to lower current and wave action, and higher salinity at depth. Age structure in the Dardanelles was relatively overrepresented in younger age classes with increasing depth. Nevertheless, this difference in age structure was not strong enough to cause trends with depth for all derived demographic parameters. In comparison with Italian populations, age structure presented a higher frequency of young individuals and were more stable in the Dardanelles, likely due to the less intense wave action. Hosting different clades of symbiotic algae may also contribute to these differences, but molecular studies are necessary to verify this hypothesis.