MICHAEL TÜRKAY & INGRID KRÖNCKE
Forschungsinstitut Senckenberg
Frankfurt a. M. and Wilhelmshaven

The eastern Mediterranean deep sea is unique in respect of its extreme oligotrophy, caused by accelerated bacterial degradation due to the high temperatures governing the deep waters.

There is only one other sea in the world which is comparable: In the Red Sea bottom temperatures are usually about 20.5°C, but the organic input from the highly productive coral reefs fringing its coasts overcompensates the quick degradation in the water column. In contrast, the Levantine Basin is much broader and its coasts are far less productive than the Red Sea reefs. Only the discharge of the Nile brings some more organic matter into the water column and the sediments, but a response of the benthos is only locally perceivable (TÜRKAY 1996)

The positive correlation of macrofauna abundance and biomass with TOC found during our studies stresses the structuring influences of nutrient input into the sediments. This is a well known fact and can be confirmed as of major importance for understanding the community structure in the eastern Mediterranean deep sea also. The vast oceanic basins depend predominantly on pelagic production, which can be uniform throughout the basin area if this is not crossed by frontal systems. The organic material reaches the bottom by sinking. In the Mediterranean, which is almost completely land-locked, lateral transport of organic matter plays a major role. The deepest parts of the Levantine and Ionian Basins are adjacent to shallower areas and are closer to the coast than the larger but shallower Levantine abyssal plains. The correlation of benthic production with distance to larger land masses is especially noticeable in the Cretan area., which shows that lateral transport in this area is probably more important than autochthonous pelagic production. The patchiness of fauna within the Ierapetra Basin as described by FIEGE et. al. (2000) accounts for a patchy distribution of different food qualities. This again must be caused by irregular food ingression events. Our results indicate that the deep Levantine Sea is an event-driven system, in which terrestrial runoff and lateral transport play a major role in the functioning of the community.

Future studies have to concentrate on describing and understanding spatial variability in community structure and its linkage to food ingression events. Only by this means will it be possible to get a better picture of the processes on which the functioning of the deep Mediterranean ecosystems is based.

Literature cited
FIEGE, D., KRÖNCKE, I & BARNICH, R. (2000): High abundance of Myriochele fragilis NILSEN & HOLTHE, 1985 (Polychaeta: Oweniidae) in the deep sea of the Eastern Mediterranean. -- Hydrobiologia, 426: 97-103.
TÜRKAY, M. (1996): Composition of the deep Red Sea macro- and megabenthic invertebrate fauna. Zoogeographic and ecological implications. In: UIBLEIN, F., OTT, J. & STACHOWITSCH, M [Eds.]: Deep-sea and extreme shallow water habitats: affinities and adaptations. -- Biosystematics and Ecology series, 11: 43-59; Wien (Österreichische Akademie der Wissenschaften).