Assessing the fish fauna diversity and abundance at Aegean and Ionian seas, with emphasis on certain NIS fish species via Scientific diving and Visual Census.

The Mediterranean Sea and its exceptional biodiversity suffer from non-indigenous (NIS) and invasive species. These result from Lessepsian migration and human activities. Species with the highest negative impact include Pterois miles, Lagocephalus sceleratus and Fistularia commersonii. The current study assessed the distribution and abundance of these three species in the Aegean and Ionian Seas in the context of the regional diversity of ichthyofauna. Using Scientific Diving and Visual Census, we focused on NIS fish fauna, and surveyed most of the areas where the occurrence or establishment of NIS had been documented. Emphasis was given to regions with limited available data. This study assessed the homogeneity of diversity and abundance of the fish species at the diving sites; assessed the most dominant species per region; and calculated relevant biodiversity indexes. Our results suggest that the south and east parts of the Aegean Sea are the most affected by the establishment of NIS. Samos Island is concluded to be an important region for the expansion of NIS to the northern parts of the Aegean Sea. Also, both the Saronikos Gulf and the whole area of the Peloponnese seem to have a pivotal role in the expansion of distribution of NIS from the east Mediterranean sub-basin to the west sub-basin. The genus Siganus seems to have very high abundances and population densities in certain areas, and therefore its establishment could have negative impacts in these regions. We conclude that scientific diving is not appropriate for monitoring the population status of L. sceleratus and we propose more appropriate methodologies such as the use of baited cameras and ROV's to be used in the future.

From seascape ecology to population genomics and back. Spatial and ecological differentiation among cryptic species of the red algae Lithophyllum stictiforme/L. cabiochiae, main bioconstructors of coralligenous habitats.

Ecosystem engineering species alter the physical structure of their environment and can create or modify habitats, having a massive impact on local biodiversity. Coralligenous reefs are highly diverse habitats endemic to the Mediterranean Sea built by calcareous benthic organisms among which Crustose Coralline Algae are the main engineering species. We analyzed the diversity of Lithophyllum stictiforme or L. cabiochiae in coralligenous habitats combining a multiple barcode and a population genomics approach with seascape features. Population genomics allowed disentangling pure spatial effects from environmental effects. We found that these taxa form a complex of eight highly divergent cryptic species that are easily identifiable using classic barcode markers (psbA, LSU, COI). Three factors have a significant effect on the relative abundances of these cryptic species: the location along the French Mediterranean coast, depth and Photosynthetic Active Radiation (PAR). The analysis of around 5000 SNPs for the most abundant species revealed genetic differentiation among localities in the Bay of Marseille but no differentiation between depths within locality. Thus, the effect of depth and PAR on cryptic species communities is not a consequence of restricted connectivity but rather due to differential settlement or survival among cryptic species. This differential is more likely driven by irradiance levels rather than by pressure or temperature. Both the genetic and species diversity patterns are congruent with the main patterns of currents in the Bay. Ecological differentiation among these engineering cryptic species, sensitive to ocean warming and acidification, could have important consequences on the diversity and structure of the coralligenous communities.