Unusual temporal variations in the spatial distribution of chlorophyll-a in the Black Sea during 1990-1996

The chlorophyll-a data set established by Turkey, Ukraine, Russia, Bulgaria and Romania was evaluated for the 1990-1996 period and only the surface chlorophyll-a was evaluated and interpreted for different parts of the Black Sea. Three well defined chlorophyll-a maxima were observed in the surface waters in the shelf region: a winter maximum in January-February, a spring-early summer one in May-June and an autumn peak in September-November. One of the expected results was the high level of chlorophyll-a concentration in shelf waters (0.02-34.0 mu gL(-1) as the range of monthly averages) compared to deep regions (0.02-2.5 mu gL(-1)) throughout the whole year. Chlorophyll-a data related to deeper central part of the Black Sea showed different and unusual trends in terms of seasonal and interannual variability's. A late winter blooming continued with slightly decreasing trend till late spring which collapsed during May. The developments of moderate mid-summer and autumn blooms were also observed. A very unusual development of phytoplankton population in 1992 mid-summer caused formation of a chlorophyll-a peak which was almost at the same order of magnitude with winter-spring bloom

Unusual temporal variations in the spatial distribution of chlorophyll-a in the Black Sea during 1990-1996

The chlorophyll-a data set established by Turkey, Ukraine, Russia, Bulgaria and Romania was evaluated for the 1990-1996 period and only the surface chlorophyll-a was evaluated and interpreted for different parts of the Black Sea. Three well defined chlorophyll-a maxima were observed in the surface waters in the shelf region: a winter maximum in January-February, a spring-early summer one in May-June and an autumn peak in September-November. One of the expected results was the high level of chlorophyll-a concentration in shelf waters (0.02-34.0 mu gL(-1) as the range of monthly averages) compared to deep regions (0.02-2.5 mu gL(-1)) throughout the whole year. Chlorophyll-a data related to deeper central part of the Black Sea showed different and unusual trends in terms of seasonal and interannual variability's. A late winter blooming continued with slightly decreasing trend till late spring which collapsed during May. The developments of moderate mid-summer and autumn blooms were also observed. A very unusual development of phytoplankton population in 1992 mid-summer caused formation of a chlorophyll-a peak which was almost at the same order of magnitude with winter-spring bloom

Long-term variations of surface chlorophyll a and primary production in the open Black Sea

Extensive data sets on surface chlorophyll a (chl a), depth-integrated primary production (DIPP) and phosphate (PO4, muM) averaged for the upper 25 m layer in 1964, 1973, 1978 and for a period (1980 to 1996) of regular measurements have been used to evaluate long-term changes in the upper portion of the euphotic layer of the entire open (>1000 m) Black Sea. After preliminary analysis of seasonal dynamics, special attention was given to data obtained during those periods of the year with relatively stable values, revealing interannual and long-term fluctuations and trends. Of 2 phytoplankton characteristics (chl a and DIPP), long-term trends were obtained only for chl a since only these data covered the entire open sea and all periods investiged. A positive correlation was found between DIPP (using 2 different C-14 methods: actual in situ and simulated in situ) and the more numerous chl a data for different monthly intervals, with significant correlation coefficients (r = 0.51 to 0.82). This means that the observed patterns in long-term variability for chl a may be valid also for DIPP, The results show that interannual fluctuations in chl a are more pronounced during the warm months, from approximately May to September. Chl a levels within this interval were moderate, with a mean of 0.15 +/- 0.04 mg m(-3) during the first 'quiet' period (1964 to 1986), but increased steadily at a rate of 0.06 mg m(-3) yr(-1) during 1988 to 1991 and sharply in 1992 (mainly due to high July values) to 0,99 +/- 0.7 mg m(-3). In contrast, negative trends were characteristic of the third period (1993 to 1996): an abrupt decrease in chl a to 0,26 +/- 0.08 mg m(-3) in 1993 and a negative trend (-0.02 mg m(-3) yr(-1)) during 1993 to 1996. Low concentrations Of PO4 (0.015 to 0.138 muM) in the upper 25 In layer throughout the year and the absence of statistically reliable interannual trends in distribution suggest that this nutrient was limiting the level of primary production during the second period. This means that phosphate concentration in the upper 25 m layer cannot be considered a reliable indicator of the presence or absence of anthropogenic eutrophication in the open Black Sea. This long-term variability in phytoplankton characteristics agrees well with the data on interannual changes in other ecological variables of the open Black Sea characterized by a collapse of the Black Sea ecosystem during the second period and its recovery after 1992. Comparison of changes in the open and shelf areas of the Black Sea between these 3 periods, and similar changes in the plankton community and in pelagic fish stocks in the second half of the 1980s to the beginning of the 1990s in other regions of the northern hemisphere, connected with changes in the climatic regime during this period, have led us to conclude that global climatic processes have played an important role in changing the phytoplankton characteristics of the open Black Sea and affecting the whole pelagic ecosystem, especially over the last 2 decades

Nutritional condition of female Calanus euxinus from cyclonic and anticyclonic regions of the Black Sea

The content and composition of lipids in Calanus euxinus females were studied in cyclonic and anticyclonic regions in the southern Black Sea during the period of persistent density stratification (September 1996). The lipid content of C, euxinus from cyclonic regions was greater than of individuals from anticyclonic regions (average 101.9 and 58.8 mu g ind.(-1), respectively). Total Lipid content (mainly wax esters, 70 to 72%, and triacylglycerols, 8 to 13%) of female C. euxinus was correlated with chlorophyll a (chl a) (mean integrated concentration) (r = 0.92, p < 0.005). The high correlation with chi a was shown also for wax ester content. used as a long-term index of food supply (r = 0.89, p < 0.05). The correlation between triacylglycerol content (a short-term index) and chi a was not significant (r = 0.66, p < 0.2). In cyclonic regions the mean integrated chi a concentration (0.38 mg m(-3)) (as an indicator of phytoplankton food biomass) was 1.7-fold higher than in anticyclonic areas. The same trend occurred for mean integrated concentrations of nitrate and phosphate (0.996 and 0.299 mu M in cyclonic and 0.438 and 0.061 mu M in anticyclonic regions. respectively) in the chi a containing layer. Thus, conditions for total primary productivity in cyclonic regions were more favorable than in anticyclonic ones. This was consistent with lipid levels in female C, euxinus

Fat content in Black Sea sprat as an indicator of fish food supply and ecosystem condition

Fat content (as % of total body wet wt) of the sprat Sprattus sprattus phalericus in the Black Sea was determined annually during the peak feeding period (i.e. summer) between 1960 and 2001. Interannual variations of this characteristic were quite high (from 8.0 to 16.0%). Sprat fat content can be used as an indicator of food supply (or recent feeding history). In the Black Sea, different periods could be distinguished with respect to food supply of this species: Period I (1960 to 1964) with stable sprat fat content values of 11.2 to 13.7 %; Period II (1965 to 1972) with decreased values of 8.5 to 10.3 %; Period III (1974 to 1982) with higher values of 11.4 to 15.7 %; Period IV (1983 to 1990) when there were the highest interannual fluctuations and a decrease to 9.9 to 10.7 %; Period V (1991 to 1997) again with high fat content values of 12.2 to 14.7 %; Period VI (1998 to 2001) with stabilized fat content values of 12.0 to 12.3 %. These periods are closely related to the general situation in the Black Sea ecosystem caused by climatic changes, increased trophic competition, eutrophication and pollution. Relationships between interannual fluctuations in sprat fat content, on the one hand, and sprat biomass and phytoplankton concentration, on the other, are revealed. The features of the interannual dynamics of the Black Sea sprat fat content are similar to those (biomass and catches) of small pelagic fishes in the Mediterranean and in some other parts of the World Ocean