No abstract

Seagrasses are flowering plants, adapted to marine environments, that are highly diverse in the Mediterranean Sea and provide a variety of ecosystem services. It is commonly recognized that light availability sets the lower limit of seagrass bathymetric distribution, while the upper limit depends on the level of bottom disturbance by currents and waves. In this work, detailed distribution of seagrass, obtained through geoacoustic habitat mapping and optical ground truthing, is correlated to wave energy and light on the seafloor of the Marine Protected Area of Laganas Bay, Zakynthos Island, Greece, where the seagrasses Posidonia oceanica and Cymodocea nodosa form extensive meadows. Mean wave energy on the seafloor was estimated through wave propagation modeling, while the photosynthetically active radiation through open-access satellite-derived light parameters, reduced to the seafloor using the detailed acquired bathymetry. A significant correlation of seagrass distribution with wave energy and light was made clear, allowing for performing fine-scale predictive seagrass mapping using a random forest classifier. The predicted distributions exhibited >80% overall accuracy for P. oceanica and >90% for C. nodosa, indicating that fine-scale seagrass predictive mapping in the Mediterranean can be performed robustly through bottom wave energy and light, especially when detailed bathymetric data exist to allow for accurate estimations.

Our understanding of the distribution of coralligenous formations, throughout but mostly on the Eastern Mediterranean seafloor, is still poor and mostly relies on presence-only opportunistic trawling and fishermen reports. Previous efforts to gather this information created relevant geodatabases that led to a first draft predictive spatial distribution of coralligenous formations in the Mediterranean Sea using habitat suitability modelling techniques. In the last few decades, the use of hydroacoustics to map the seafloor for various geotechnical and habitat mapping projects accumulated high amounts of detailed spatial information about these formations, which remains majorly unexploited. Repurposing these datasets towards mapping key habitats is a valuable stepping stone to implementing the EU Habitat Directive. In Greece, a unique volume of seafloor mapping data has been gathered by the Laboratory of Marine Geology and Physical Oceanography, Geology Department, University of Patras. It accounts for more than 33 marine geophysical expeditions during the last three decades, having collected hydroacoustic data for a total seafloor area of 3,197.68 km2. In the present work, this information has been curated, re-evaluated, and archived to create the most complete, until now, atlas of coralligenous formations in the Greek Seas and the only integrating presence–absence data. This atlas has been used to train and validate a predictive distribution model, incorporating environmental variables derived from open data repositories, whose importance has been assessed and discussed. The final output is an improved probability map of coralligenous formation occurrence in the Greek Seas, which shall be the basis for effective spatial planning, gap detection, and design of future mapping and monitoring activities on this priority habitat.

No abstract