|Mediterranean pelagic habitat. Oceanographic and biological processes, an overview|
Wurtz, M. (2010). Mediterranean pelagic habitat. Oceanographic and biological processes, an overview. IUCN: Gland & Malaga. ISBN 978-2-8317-1242-0. 88 pp.
The Mediterranean Sea is a highly variable and dynamic environment, with very high biologic diversity. Between 4% and 18% of the world’s marine species are found in the Mediterranean, even though it represents only 0.82% in surface area and 0.32% in volume of the world oceans : more than a quarter of these species are endemic to the Mediterranean. The Mediterranean Sea and its pelagic environment are also of great economic importance to the surrounding countries. This document is the first part of a project conducted by The World Conservation Union, IUCN, in an attempt to describe the functioning of the Mediterranean Sea and the threats to the ecosystem, and further to discuss solutions and provide a model for formulating protection plans. The high variability of the Mediterranean ecosystem brings the need for special actions and dynamic protection. The high level of biodiversity in the Mediterranean Sea can be explained by its geological history, in which the rate of environmental change, and thus species occurrence, has been exceptionally high. Moreover, the present variety of climatic and hydrologic situations found within the Mediterranean pelagic ecosystem allows for the presence of both temperate and subtropical species. The Mediterranean Sea is unique, being a semi-enclosed sea connected to the Atlantic Ocean through the narrow Strait of Gibraltar, to the Red Sea by the man-made Suez Canal and to the smaller enclosed Black Sea via the narrow Bosphorus Strait. The Mediterranean Sea exchanges water, salt, heat, and other properties with the North Atlantic Ocean, and is thus an important actor, affecting global water formation processes and variability and subsequently the stability of the global thermohaline state of equilibrium. Water from the Atlantic enters the Mediterranean Sea through the Gibraltar Strait, circulates in Mediterranean basins, undergoing evaporation and depletion of nutrients, sinking in certain areas and becoming transformed into the salty, nutrient-poor Mediterranean water that later returns to the Atlantic through the Strait of Gibraltar. Mediterranean circulation is driven by water exchange through the various straits, by wind stress, and by freshwater and heat fluxes causing buoyancy flux on the surface. The patterns and processes are complex and highly dynamic, including free or boundary currents and jets, bifurcating, meandering, growing and shedding ring vortices. These features create a landscape of dynamic habitats whose location, extent and shape changes through time. There are also permanent and recurrent sub-basin scale cyclonic and anticyclonic gyres, ocean fronts, upwelling areas, and small but energetic mesoscale eddies. All these hydrographical structures are associated to various transition domains, i.e. narrow regions of strong temperature and salinity gradient. Transition domains are of particular biological and ecological importance, maybe most significantly as being breeding and nursery grounds for a wide range of organisms. They are also associated with a high and predictable primary production, making them important foraging areas with high prey aggregation, and with changes in type and abundance of marine organisms. These structures also serve as migration routes for highly mobile species, such as marine mammals and other top predators. Human activities have a large impact on physical, chemical and biological environment, which leads to ecological changes, and sometimes to permanent ecosystem shifts. Given the variability of the Mediterranean pelagic ecosystem and its dynamic habitats, a broad-based, dynamic conservation approach is needed to preserve essential ecological processes and services, and to protect economic and cultural resources for future generations. Hence, this project aims to apply a process approach to habitat conservation, seeking to ensure that not only the pelagic marine species, but also the dynamic pelagic habitats upon which they depend, are considered when Marine Protected Areas (MPAs) are formed. A particular aim of this project is trying to characterize which physical and biological characteristics make certain ocean habitats more suitable than others, and to determine if the processes are persistent and predictable enough in space and time to warrant designation as MPAs.