X hits on this document

PDF document

An introduction to Mediterranean deep-sea biology* - page 18 / 32





18 / 32

ecosystem to climate variability on a decadal scale. Because the Mediterranean Sea behaves as a minia- ture ocean (Bethoux et al., 1999), changes that occur in the eastern Mediterranean can be used as a model of the potential instability of the oceanic circulation. Such a model would help our understanding and our predictions of the impact of climate change in deep seas worldwide (Lascaratos et al., 1999). Indeed, Danovaro et al. (2001), report that in the past decade, extensive climate change has modified the physico-chemical characteristics of deep waters in the eastern Mediterranean. Climate change has caused an almost immediate accumulation of organ- ic matter on certain areas of the deep-sea floor, altered the carbon and nitrogen cycles and had neg- ative effects on deep-sea bacteria and benthic fauna. They propose a miniature ocean model in an attempt to provide new ways of interpreting signals from the deep sea. Their approach indicates that contrary to what might have been expected, deep-sea ecosys- tems do respond quickly to climate change.

The deep Mediterranean differs from the better- known oceanic abyss in terms of its physical envi- ronment, food supply and degree of inter-specific interaction (both competition and predator-prey), any of which could influence the physiological char- acteristics of the fauna present. Influences may be direct (e.g. effects of temperature on metabolism) or, given sufficient time, through selection of advanta- geous traits. In the case of the deep Mediterranean, has there been sufficient time and selective pressure for adaptation, or are these just cold-water animals surviving in a warm sea?



The Mediterranean Sea is a semi-enclosed sea characterised by a continental shelf most frequently reduced to a narrow coastal fringe and covering less than 30% of the total area. The bathyal ground extends for about 60% of the whole basin, whereas the abyssal plane covers about 13% of the bottoms. Despite these differences in the extension of the bot- tom types, most of the Mediterranean living resources are exploited on the continental shelf, where a high variety of species and biocoenoses occur and many fishing techniques and related activ- ities have long been carried out. In spite of the long history of biological resource harvesting in the

24 F. SARDÀ et al.

Mediterranean coastal areas (Caddy, 1993; Farrugio et al., 1993), the exploitation of deep-sea organisms started only in the first few decades of the last cen- tury due to the development of the technology for seeking in deep waters. In particular, the red shrimps Aristaeomorpha foliacea and Aristeus antennatus began to constitute the target of deep-water bottom trawl fishing in the 1930s in the Ligurian Sea, where the first trawlers that sought the epibathyal depths managed to catch between 100 and 200 kg d-1, and in some periods, after the second world war, the cap- tures went up to 1000 kg d-1 per boat (Relini and Orsi Relini, 1987). Nevertheless, it was not until the middle 1940s when its importance as an exploited resource was evidenced in the Catalan and Balearic seas (Arté, 1952; Bas et al., 1955; Bas, 1960; Mas- sutí, 1961; Maurin, 1965a, b; Relini-Orsi and Relini, 1972; Massutí and Daroca, 1978), and it was point- ed out as one of the latest fisheries developed in the Mediterranean.

Western Mediterranean fisheries

Though fisheries down to a depth of 700 m have been usual since the middle of the last century in the Mediterranean sea, the deep-sea bottoms down to 1000 m are still totally pristine. At these depths there are no specialised fisheries as in other parts of the world such as Canada and Australia. However, the trawl bottom fishery currently goes down to almost 1000 m. This deep trawl bottom fishery is carried out due to two fundamental factors. The first one is the narrowness of the shelf, crossed by numerous submarine canyons. This brings the deep depths within a few miles of the coast. The second one is the human density of Mediterranean regions and the high demand for marine products, which are traditional in the Mediterranean diet. These factors generate high competition between fishermen. The Mediterranean sea is considered an oligotrophic sea and is characterised by over-exploitation of its marine resources, this over-exploited situation began in the 1980s. The trawl boats that work on deep-sea grounds have powers of between 300 and 1800 CV. Boats of wood or iron have now been replaced by boats of glass-fibre and of a catamaran type with high technologies. However, mixed enter- prises to exploit the deep-sea ground of North Africa are now common. The deep-sea rose shrimp, Aris- teus antennatus (Risso, 1816) (Crustacea, Decapo- da, Dendrobranchiata, Aristeidae), is the most important fishery in the western Mediterranean Sea

Document info
Document views116
Page views116
Page last viewedMon Jan 23 19:17:03 UTC 2017