Inequitable protection of multidimensional biogeochemical regions in the Mediterranean Sea

In many cases, protected areas are placed opportunistically and do not fully capture the representation of ecological components for achieving biodiversity conservation goals. In marine systems, where threats and biodiversity are inherently multidimensional and include vertical depth gradients, the designation of protected areas can be more challenging than in the terrestrial realm. Here, we aimed to evaluate the representation equality of biogeochemical regions at different depths in the Mediterranean Sea as a surrogate for biodiversity. We conducted a gap-analysis evaluating the current extent and coverage of protected areas in the Mediterranean Sea biodiversity hotspot to achieve an equitable representation and conservation strategy for the basin. We used biogeochemical regions across different depths, which allow more complex 3D marine spatial planning that includes spatial complexity of marine systems. A total of 60 biogeochemical regions distributed across three bathomes (spaces determined by depth; i.e. epipelagic, mesopelagic, and bathypelagic zones) and the seafloor were assessed. We found that biogeochemical regions in the Mediterranean Sea were not equally protected across bathomes, and that global conservation targets were not met. The bathypelagic bathome had the lowest representation in the Mediterranean Sea marine protected area (MPA) network, as well as the lowest protection equality. The sub-basins with highest protection included the Algero-Provençal basin and the Tyrrhenian Sea. These two sub-basins were the only ones that passed the Aichi protection target of 10%, while all others were lower than the target. The Ionian Sea was identified as the most highly diverse sub-basin regarding biogeochemical regions but with the least protection and with low conservation equality, making this sub-basin a high priority for conservation. Amongst countries, non-European Mediterranean countries had lower values of protection and conservation equality metrics. In general, the bathypelagic bathome was found as the least protected, the most fragmented, and with the lowest protection equality, thus its protection should be enhanced through all the Mediterranean Sea. Decision makers in the Mediterranean can apply the gap-analysis approach presented here as a useful starting point for improving protection equality in the region, incorporating these metrics in the evaluation of new proposed protected areas and sites for conservation.