Identifying sites for Deep Sea MPAs

Identifying sites for Deep Sea Marine Protected Areas

In the high seas, priorities for protection will focus on deep-sea communities because they contain a high level of endemic species and unique but extremely vulnerable habitats. Deep-sea species mainly inhabit continental slopes, submarine canyons, and seamounts. The western Mediterranean is higher in overall abundance and diversity of deep-sea taxa than the eastern Mediterranean. These patterns may be explained by the Tethys hypothesis suggesting that Mediterranean ecological communities are Atlantic relics of the Messinian episode, when the Mediterranean basin sealed and almost completely desiccated. An alternative hypothesis suggests that Mediterranean fauna are satellite populations dependant on East Atlantic larval replenishment, through the Strait of Gibraltar, for the maintenance of its populations.
 

Deep-sea sponge communities like this one are particularly vulnerable to trawl fisheries

The low food input to the deep sea results in scarce food resources, high food partitioning, highly diversified diets, and very complex trophic webs. Assemblages in waters deeper than 1000m exhibit extremely low productivity, and as such they may be particularly vulnerable to human influences. The main anthropogenic impacts on these communities are:

  • Removal of top predators by fishing and removal of habitat-forming species such as gorgonian (e.g. Isidella elongata) and cold water coral species (e.g. Lophelia pertusa and Madrepora oculata) by deep-sea trawling
  • Modification of trophic links between species in food webs by discarding by-catch and the subsequent and unorthodox use by species
  • Accumulation of heavy metals and toxins in specific areas of the deep sea due to marine pollution that is channelled by submarine canyons
  • Global climate change will affect the quality and quantity of food that reaches deep-sea communities

A recent study by IUCN and WWF has identified sites that need to be protected (see Figure). An important criterion in the identification of deep-sea MPAs is the type and number of endemic species in an area. Although 26% of Mediterranean species are estimated to be endemic, an overall estimate is not available for deep-sea species. Thus far it is known that there are at least 14 species (6 fishes, 4 decapods and 4 echinoderms) endemic to deep-sea Mediterranean ecosystems. The most unique high-sea and deep-sea ecosystems are associated with cold seeps, brine pools, cold water coral mounds, and seamounts. Tudela et al. propose a system of deep sea marine protected areas that is representative of these unique habitats and based on a distribution of 35 unique, deep-sea biocenoses in the Mediterranean. As a result, a ban on fishing in areas deeper than 1000m has been adopted by the General Fisheries Commission for the Mediterranean (GFCM).

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Mediterranean landscape
The Mediterranean deep-sea ecosystems: An overview of their structure, functioning and anthropogenic impacts