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An introduction to Mediterranean deep-sea biology* - page 14 / 32





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benthic macrofauna composition of the deep Mediterranean Sea, quantitative data from this basin are generally scarce or lacking. It is not an exagger- ation to say that the vast majority of the deep Mediterranean basin is virtually unknown. Despite the interest of its fauna, the eastern Mediterranean, the deepest of the two basins, remained one of the most poorly studied areas of the world until the early 1990s. During the second half of the 20th century research was sparse, with only some general ecolog- ical and faunal surveys conducted in the Mediter- ranean providing scattered information (Pérès and Picard, 1958; Tchukhtchin, 1964; Ledoyer, 1969; Guille, 1970; Desbruyeres et al., 1972; Vamvakas, 1970 and 1973; Di Geronimo, 1974). The earliest records of macrobenthic organisms from the Cretan Sea were those given by Forbes (1844), Raulin (1870) and Jeffreys (1881, 1883). However, with the establishment of the Institute of Marine Biology of Crete, a number of benthic studies have appeared in the last twelve years (Tselepides, 1992; Tselepides and Eleftheriou, 1992; Koutsoubas et al., 1992, 2000; Tselepides, 1994; Karakassis and Eleftheriou, 1997; Eleftheriou et al., 1996; Tselepides et al., 2000), contributing significant information to the knowledge of the macrobenthic fauna mainly from the outer continental shelf to the upper and mid- slope of the island of Crete.

Until recently, however, knowledge of the deep (bathyal to abyssal) macrobenthic fauna remained sparse, derived primarily from material collected during the early “POLA” Expedition (1890-1893) in the eastern Mediterranean (Sturany, 1896) and to a lesser extent from the METEOR expeditions in 1987, 1993 and 1998 (Janssen, 1989; Fiege et al.,

1994, 2000; Ben-Eliahu and Fiege, 1996). It was not until recently (1987-2000) that a coherent sampling effort was undertaken, mainly within the framework of EU funded projects, but even so the number of reliable quantitative macrobenthic samples acquired is very low (probably less that 100), as most of these studies were conducted as part of large multidisci- plinary biogeochemical projects and therefore little effort and time was devoted to sampling the benthic community.

Several investigations have described low-densi- ty and low-diversity conditions of marine inverte- brates in the eastern Mediterranean (Pérès and Picard, 1958; Fredj and Laubier, 1985; Janssen, 1989; Tselepides and Eleftheriou, 1992; Tselepides et al., 2000). Por and Dimentman (1989) mentioned that a safe hypothetical figure concerning the impoverishment in the general diversity of the marine biota in the Levantine Basin would be 30%. The bathyal muds of the Levantine basin have also been reported as being inhospitable or even azoic after the last “sapropelic event” (Menzies, 1962, 1973; George and Menzies, 1968; Bacescu, 1985). Tselepides et al. (2000), in the Cretan Sea, reported that mean benthic biomass, abundance and diversity (Fig. 2) decreased drastically with depth, with major faunal transitions occurring at 200, 500 and 1000 m depth. Unexpectedly, the western basin has also been grossly understudied, with very few quantita- tive studies focusing on the bathyal and abyssal macrofauna. A comprehensive quantitative approach was undertaken by Stora et al. (1999) with samples taken within and along the flanks of the Toulon Canyon. Other recent studies have focused mainly on functional aspects such as gradients of

FIG. 2. – Hurlbert’s expected number of species from the continental margin of Crete (from Tselepides et al., 2000).

20 F. SARDÀ et al.

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