Evaluation of habitat distribution and human imprints around an insular open-pit, Gyali Island, Southeast Aegean Sea

Gyali is a small volcanic island in the Dodecanese. The present study used a high resolution hydroacoustic dataset, validated by camera and sediment samples, in order to investigate the habitat distribution, to compare sonar and satellite information regarding the distribution of seagrass and to detect potential anthropogenic imprints in the marine environment due to the onshore extraction activities. The seafloor has an uneven morphology and is characterized by numerous fluid seepages probably of hydrothermal origin, either extended or isolated. Side scan sonar analysis revealed six reflectivity types corresponding to specific seafloor morphology and consistency. Those were attributed to five marine substrates/habitats: sand, rippled sand, gravel-rhodoliths, P. oceanica, and reefs/rocky relief. Evidence of locally intense hydrodynamics was also observed. Satellite data concerning the spatial extent of seagrass was compared with the sonar recorded distribution, revealing significant differences, with only 44% of the total area mapped using satellite data corresponding with seagrass mapped in the present study. Anthropogenic targets related to anchor and mooring scars (few of them running through seagrass meadows) and other debris were detected scattered on the seafloor, mainly to the east and south of the island. Yet, the overall appearance of the habitat distribution and the visual inspection findings did not suggest considerable pressures from the onshore mining activities, even though biodiversity and other environmental studies need also to be implemented to confirm this conclusion.