The bioluminescence field as an indicator of the spatial structure and physiological state of the planktonic community at the Mediterranean Sea basin.

The purpose of this work is to show the possibilities of using the characte ristics of the bioluminescent fields to monitor the marine planktonic commu nities. The data bank contains 3500 vertical casts of bioluminescent potent ial and near 1000 planktonic organisms obtained at 500 oceanographic statio ns executed in 21 expedition to the Mediterranean Sea basin in 1970-1995. S tudies were carried in different seasons in the Mediterranean and the Black Seas where different trophic conditions and considerably different species composition and abundance occurred in the phytoplankton. There are of coar se differences between abundance of various dinoflagellates and an intensit y of measurement of bioluminescence, but the main features of these appeare d to be similar, the intensity of bioluminescence increased in proportion t o their number and physiological state. Seasonal changes are also well developed and mostly in the Black Sea. Two i ntensive periods of bioluminescence were recorded , one in May-June and the other one, more intensive, in October-November. The bioluminescent potenti al was achieving 1.4 10(-2) microwatt cm(-2) l(-1), which exceeded minimum numbers in February 500 times. Seasonal cycles are weakly developed in the ogliotrophic regions in the Mediterranean Sea: differences of the biolumine scent potential between summer and winter periods achieve 3.5 times only. Macroscale trends of bioluminescence changes within the Mediterranean basin are comparable with that of the plankton spatial distribution. General tre nd of bioluminescence increase, from the Aegean Sea to the west and from th e Algerian coast to Spain, was evaluated on the basis of the whole basin. B ioluminescence in the central part of the Black Sea is 3 times weaker than in the Alboran Sea. However, it is one order higher than that in the centra l part of the Mediterranean Sea. As we have stated there are regions of "clean" and "polluted" waters in bot h nertic and open sea waters. For example, in the Mediterranean Sea the sen tral regions of the Alboran, Ionian and Aegean Seas, and the central part o f the western gyre and Karadag marine reserve of the Black Sea were all con sidered to have relatively good water quality while the regions of the inte nsive shipping (straits, southern part of the Ionian Sea near-Bosphorus reg ion. Black Sea north-western part) and densely inhabited riparian zones(Cri mean southern coast) were considered to be regions of "ecological risk". Th ere are considerable differences between the parameters of the regression l ines from the studied regions. For example, to obtain the same bioluminesce nce intensity in the 0-100 m layer, the quantity of dinoflagellates in poll uted regions of the Mediterranean Sea would have been twice as abundant as those from "clean" waters. Similarly the numbers of bioluminescent algae in the Black Sea would have increased 3-4 times to obtain the same biolumines cent intensity. As the anthropogenic pressure in the Black Sea is higer, du e to the population density in the river drainage areas and to the low wate r exchange the differences are more apparent. It can be presumed, that an o rganism's metabolic state (and hence its bioluminescence) could serve as an indicator for the levels of pollution in the environment.