Spatial patterns of Posidonia oceanica structural and functional features in the Eastern Mediterranean (Aegean and E. Ionian Seas) in relation to large-scale environmental factors.

In the context of general ecosystem monitoring of the Greek coastal marine environment, a total of 22 descriptors of Posidonia oceanica meadows were studied in 69 study sites. Spatial variation of P. oceanica meadows' features in relation to specific environmental factors (i.e., light, physical exposure, temperature, and nutrients) controlling their dynamics was assessed in three sub-ecoregions of the Hellenic seas (Eastern Ionian, North Aegean, and South Aegean). The studied meadows differentiated by exhibiting varying growth patterns at both the local and sub-ecoregional scale. Significant differences in morphological and demographic descriptors were observed for meadows of the N. Aegean Sea as compared to those of the S. Aegean and the Eastern Ionian Seas. Light limitation was determined as the main driver differentiating the P. oceanica meadows' distribution (i.e., lower limit depth), demography (i.e., shoot density, meadow cover) and shoots' biometry (i.e., shoot length, shoot leaf surface and leaf biomass) along the mainland coastal zone of the N. Aegean Sea. Considering the projected decline of P. oceanica in the face of increasing natural and human impacts, this study offers a crucial ecological baseline that can enhance our understanding of P. oceanica meadows' trends, against which the efficiency of conservation plans and management actions may be monitored.

Cumulative impacts from multiple human activities on seagrass meadows in eastern Mediterranean waters: the case of Saronikos Gulf (Aegean Sea, Greece).

Ecosystem-based management (EBM) addresses the fundamental need to account for cumulative impacts of human activities with the aim of sustainably delivering ecosystem services. The Saronikos Gulf, a large embayment of the Aegean Sea, provides a wide range of ecosystem services that are impacted by multiple human activities, deriving from the metropolitan area of Athens (situated at the northeast part of the Gulf). The anthropogenic impacts affect the status of several marine ecosystem components, e.g., seagrass meadows. Cymodocea nodosa meadows are only present at the most confined western part of the Gulf, whereas Posidonia oceanica meadows are mainly distributed in the inner and outer part of the Gulf. The aim of this study is to assess the cumulative impacts from multiple human activities on the seagrass meadows in the Gulf. The main results indicated that most impacted meadows are P. oceanica in the inner part of the Gulf, adjacent to the most urbanized coastal areas, and near port infrastructures. Land-based pollution, as well as physical damage and loss seem to be the main pressures exerted on the meadows. Understanding cumulative impacts is crucial for informing policy decisions under an EBM approach.

Ecoregion-based conservation planning in the Mediterranean: dealing with large-scale heterogeneity.

Spatial priorities for the conservation of three key Mediterranean habitats, i.e. seagrass Posidonia oceanica meadows, coralligenous formations, and marine caves, were determined through a systematic planning approach. Available information on the distribution of these habitats across the entire Mediterranean Sea was compiled to produce basin-scale distribution maps. Conservation targets for each habitat type were set according to European Union guidelines. Surrogates were used to estimate the spatial variation of opportunity cost for commercial, non-commercial fishing, and aquaculture. Marxan conservation planning software was used to evaluate the comparative utility of two planning scenarios: (a) a whole-basin scenario, referring to selection of priority areas across the whole Mediterranean Sea, and (b) an ecoregional scenario, in which priority areas were selected within eight predefined ecoregions. Although both scenarios required approximately the same total area to be protected in order to achieve conservation targets, the opportunity cost differed between them. The whole-basin scenario yielded a lower opportunity cost, but the Alboran Sea ecoregion was not represented and priority areas were predominantly located in the Ionian, Aegean, and Adriatic Seas. In comparison, the ecoregional scenario resulted in a higher representation of ecoregions and a more even distribution of priority areas, albeit with a higher opportunity cost. We suggest that planning at the ecoregional level ensures better representativeness of the selected conservation features and adequate protection of species, functional, and genetic diversity across the basin. While there are several initiatives that identify priority areas in the Mediterranean Sea, our approach is novel as it combines three issues: (a) it is based on the distribution of habitats and not species, which was rarely the case in previous efforts, (b) it considers spatial variability of cost throughout this socioeconomically heterogeneous basin, and (c) it adopts ecoregions as the most appropriate level for large-scale planning.