Changes In Productivity Of The Black Sea And Some Practical Recommendations For It’s Protection
CHANGES IN PRODUCTIVITY OF THE BLACK SEA AND SOME PRACTICAL RECOMMENDATIONS FOR IT\’S PROTECTION
B. Alexandrov
Odessa Branch Institute of Biology of Southern Seas, National
Academy of Science of Ukraine
According to the Strategic Action Plan for the Rehabilitation and Protection of the Black Sea [9] eutrophication is the first reason of degradation of the Black Sea ecosystem. Eutrophication means sharp increasing influx of nutrients, which have a strong impact on rates of primary production [6].
A marked increase in the productivity of shelf ecosystems due to eutrophication had a different effect on other components of their biological structure. The increasing amounts of nutrients influenced the pelagic organisms. Their average biomass in the Black Sea rose in 3-30 times. However, salutation of the seabed, the subsequent decreasing in water transparency and oxygen regime caused a 5-10 fold drop in the numbers and biomass of benthic organisms. The catches of plankton feeding small fishes (anchovy and sprat) increased more than two fold [7]. When defining the general changes in the biological structure of the Black Sea ecosystem, an increase in small sized, short cycle species was observed [13]. In other words, eutrophication was favorable for organisms with higher productivity. Owing to this situation, it has been confirmed that with the changing conditions of the ecosystem that has taken place during a rise in trophic status, there has been a disturbance in the stability and the ecological niches formed by the invading highly productive species, which are more adapted to new conditions. For example, changes in biodiversity of the northwestern shelf, as most productive zone of the Black Sea, lead to preferred development of species with a specific production more than 2.4 in the composition of phytoplankton, 1.2 - zooplankton and 0.012 - macrophytobenthos. Changes in the functional activity of plankton and benthos due to restructuring of their biological structure during eutrophication were similar and doubled in comparison to the 1960-1970s [3].
The increase of a food supply of plankton feeding fish has entailed increase of their number on the average in 1,5-2 times. About 90 % of them make the most small-sized and cheap. At the same time the catches of the bottom feeding fish declined as a result of eutrophication. Taking into consideration that the majority of these fish is valuable, it is possible to draw a conclusion, that the overall costs of fish reserves of northwest shelf has decreased, as it is demonstrated on the example of the Danube river mouth zone (Tab. 1).
Table 1. Changing in species composition and quantity characteristics of the ichthyofauna in the Danube river mouth zone of the Black Sea and some economic evaluations
Species
Market price,
Grn*/kg
Before eutrophication**
(1956 – 1959)
After eutrophication ***
(1995 – 1997)
Average annual catch, tons
Share of catch, %
Total price,
millions Grn
Average annual catch, tons
Share of catch, %
Total price,
millions Grn
Plankton feeding fish
Sprat
2,00
1398,4
42,31
2,797
3933,0
83,15
7,866
Anchovy
3,00
826,1
25,00
2,478
249,0
5,26
0,747
Danube shad
4,00
13,1
0,40
0,052
163,3
3,45
0,653
Black Sea scad
4,00
498,5
15,08
1,994
30,7
0,65
0,123
Bonito
10,00
189,8
5,74
1,898
0,0
0,00
0,000
Mackerel
8,00
94,3
2,85
0,754
0,0
0,00
0,000
Total
3020,2
91,38
9,973
4376,0
92,51
9,389
Bottom feeding fish
Great sturgeon
30,00
38,3
1,16
1,148
0,0
0,00
0,000
Russian sturgeon
25,00
5,8
0,18
0,145
0,7
0,01
0,018
Starred sturgeon
17,00
3,1
0,09
0,053
0,0
0,00
0,000
Grey mullet
5,00
2,5
0,07
0,012
0,3
0,01
0,002
Turbot
9,00
152,0
4,60
1,368
0,0
0,00
0,000
Flounder
9,00
2,2
0,07
0,019
23,7
0,50
0,213
Total
203,7
6,16
2,745
24,7
0,52
0,232
Others
0,10
81,0
2,45
0,008
329,5
6,96
0,033
Total
3305,0
100,00
12,726
4730,1
100,00
9,654
*Rate of exchange is 1 USD= 5.00 Grivnyas (Grn)**According N.E. Salnikov [8]; ***According the data of Danube Biosphere Reserve (A. Voloshkevich – personal communication).
Dollar adjustment for property damage on living resources is the most prevailing and effective method among economic instruments of rehabilitation and protection of the Black Sea ecosystem. It is well known that for calculation of the total sum of the damage on fish resources in countries former USSR use average value of phytoplankton, zooplankton, zoobenthos biomass and their annual specific production (P/B). At the same time in contrast to biomass the values of specific production assume as constants in equation of damage calculation [11]. By the way it is necessary to note that these values of specific production have been identify for period before intensive eutrophication and base on the data measurement collected in 60-70s.
The aim of present investigation was to determine the modern values of specific production of the Black Sea phytoplankton, zooplankton, zoobenthos and compare the difference between results of calculation of fee for the damage according to the modern and accepted (standard) values.
Investigated area was the Danube river mouth zone of the Black Sea as one of the richest in fish resources and mostly eutrophicated part of the sea. For the P/B calculations data of quantity investigations of aquatic organisms in different seasons of 1995-1999 were used. There were analyzed 81 samples of phytoplankton, 86 samples of zooplankton and 59 samples of zoobenthos. Biomass and production of all investigated organisms were identified with the help of equations from the papers: for phytoplankton [5, 10] and for pelagic and benthic invertebrates [1, 2].
The increase of the updated annual specific production (Р/В-coefficients) comparing to the base standards for a plankton (in 1,5-3 times) and benthos (in 1, 2 times) influenced the value of demagnification during calculations. Another source of inaccuracy of P/B\’s determination is to fail to take into account the real water temperature during investigated period. The significant role in living conditions of aquatic organisms has not only absolute value of temperature, but it gradient (rate of change). Using this parameter it is possible conditionally to divide year into the main temperature periods. For the Danube influence zone in the Black Sea three time intervals were determined on the base of long-term changes of temperature [4]. The greatest degree of deviation of updated P/B values from normative (standard) is registered in the warm-water period. In particular the values of P/B were 3-5 times higher for pelagic organisms and 1,7 times - for zoobenthos (see table 2).
Thus it is possible to conclude, that for present ecological situation in the Black Sea, the application of existent method in calculation of damage to fish reserves from loss of fodder organisms causes the significant deviation from reality. In average the calculated total fish biomass understates in 1,5time for plankton feeding fish and in 1,2 times for bottom feeding fish, if the standard not corrected method of calculation is used [11]. Moreover the existent method of calculation has some deficiency in methodical order. Accepted values of P/B coefficients are adopted for the annual period. In this situation there is no possibility to take into account the seasonal changes of external natural factors, such as temperature, considerably oscillating during the year. So, in could-water period (January-March) the damage counted on the basis of standard values of P/B leads to the overshoot of results in 1,5-3times, but during the rest part of the year (9 months) it is undervalued in 1,3-3 times (Tab. 2).
Table 2. Seasonal differences between the standard (St) and updated (Up) values of specific production of feeding organisms in Danube influence zone
Time intervals*
Feeding objects
Specific production
Deviation, %
St
Up
1 January - 20 March
(Water temperature,
Т
C
Phytoplankton
0,685
0,452
66
Zooplankton
0,090
0,121
134
Zoobenthos
0,007
0,001
14
21 March - 20 May
13 October - 31 December
(Т= 5,0 - 15,50С)
I
Phytoplankton
0,685
0,962 ± 0,605
140
Zooplankton
0,090
0,216 ± 0,099
240
Zoobenthos
0,007
0,008 ± 0,003
100
21 May - 12 October
(Т > 15,50С)
W
Phytoplankton
0,685
1,939 ± 0,166
283
Zooplankton
0,090
0,536 ± 0,194
595
Zoobenthos
0,007
0,010 ± 0,001
143
Average annual
Phytoplankton
250,0
561,0
224
Zooplankton
32,8
123,9
378
Zoobenthos
2,6
3,1
119
*Time intervals: C - cold-water, I - intermediate, W - warm-water.
Above-stated facts enable to recommend application of seasonal Р/B-coefficients together with calculation of the temperature correction using existing method [12]. The similar approach will enable to promote realization of economic activities in winter season, when the damage is minimum and to minimize effect on water ecosystem in high temperature period of the year, when the probability of negative consequences considerably increases.
Possible recommendations:
– elaborate and approve the system of biological indicators and gradation of their values to identification of the different trophic levels of sea area;
– carry out the division of the Black Sea area into zones (districts) with different trophic level on basis of biological indicators of eutrophication;
– improve existent method of determination the damage to marine ecosystem in define more exactly the average specific production of it basic components (phytoplankton, zooplankton, zoobenthos) for different zones of the Black Sea.
ACKNOWLEDGMENTS
The author would like to thank Dr. D.A. Nesterova, Dr. L.N. Polyschuk and I.A. Sinegub (Odessa Branch, Institute of Biology of the Southern Seas) for phytoplankton, zooplankton and zoobenthos data.
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