International Council for theExploration of the Sea

CM 2OOO/M:29Theme Session on Environment -

Plankton - Fish Linkages

REASONS OF PLANKTON BIOMASS DYNAMICSIN THE SOUTHERN BARENTS SEA

S.S.Drobysheva and V.N.Nesterova

Polar Research Institute of Marine Fisheries and Oceanography (PINRO),6 Knipovich Street, 183763, Murmansk, Russia

Barents Sea water masses variety and latitudinal extent of this reservoir createsspatial heterogeneity of its population zoogeographical composition and temporalshifts of seasonal biological processes in different sea areas (Bogorov, 1941). Itdetermines the dynamics of local systems’ productional level . These variationsdepend on the activity of the Gulf Stream, which advection of warm Atlanticwaters is extremely important for keeping up the life in severe polar waters(Zenkevich, 1963 j.

The extent of Atlantic advection influence can be judged by the distribution ofwater masses and water exchange intensity (Dobrovolsky, 1961; Tantsura, 1959;Mukhin, 1975; Kudlo, 1961). In accordance with the distribution of Atlantic waters,the south-western sea is inhabited by boreal fauna and the north-east - by thearctic one (Deryugin, 1915; Hofsten, 1916; Filatova, 1938). The boundary betweenthem almost coincides in different ecological groups of marine organisms (plankton,benthos, necton). It is located at the level of 35-40”E (Cheremisina, 1948) andits year-to-year position depends on annual shifts of faunisic complexes. Theinfluence of water masses on plankton is more indicative. Its composition andabundance at the eastern border of the Atlantic waters penetrating into theBarents Sea is reliably recorded in the Kola Meridian hydrographic section(33’ 30’ E) crossing three Atlantic flows - the coastal and main branches of theMurman Current and the Central Branch of the North Cape Current (Tantsura,1959).

The first mass collecting mesoplankton in the Kola Meridian Section was carriedout by the State Oceanographic Institute of the USSR Academy of Science in1929-1930, and in 1959 PINRO started to conduct regular annual plankton surveys,which were in progress till 1993. In total, 660 plankton samples were collected.

Already at the first stage of all-the-year-round investigations, in the 3Os, the idea ofextraordinary homogeneity of plankton specific structure all over the latitudinallength of the section with predominating group of Calanoida, among whichC.finmarchicus made up 80-90% of the total biomass; of the short-tetm summerperiod of plankton intensive development with abrupt increase in biomass; of thelatitudinal shift of growth peak along the Kola Section during summer months

2

(Yashnov, 1939) was given.. The displacement of development “wave” along thesea area corresponds to the periods of plankton spring-summer growth in differentlatitudes (Drobysheva, Nesterova, Nesvetova, 1988) (Fig.1). Based on it , it wasassumed, that reproduction of C.finmarchicus in the Barents Sea was monocyclicand that the southern (Atlantic) and northern (the Arctic Ocean) groups with aboundary at the level of 73-74’N represented different populations not related toeach other genetically and different in biological characteristics (Yashnov, 1939).

Those propositions became initial when our analysing structural and quantitativedynamics of C.jkmarchicus southern group status by the data from collectingplankton in the Kola Meridian Section in the 60-9Os, in the period of biomassreaching maximum in summer (May-June), and concentrating in the surface 50 mwater layer. The purpose was to clear up the reasons of variability of the mainpopulational characteristics of C.jnmarchicus from the southern group.

The period investigated was characterised by prolonged cooling following theintensive warming in the 20-40s and lasted till the 90s with minute exemptions(1973-1975) (Kudlo, Shpaikher, 1973; Mukhin, 1975). Therefore, cold (1978, 1979,I980, 1981) and warm (1983, 1984, 1990, 1991) years of that period were themost indicative.

During all the years specific composition of May-June plankton southern group inthe surface waters became enough stable. Against the unchangeable predominanceof boreal C.jkmarchicus only small changes in specific structure due to the portionof minor small copepods fluctuating and appeared species-indicators of warm andcold waters took place. In cold years the number of Pseudocalanus eZongutusdecreased and typically cold water species Metridia longa and Aeginopsisappeared, the number of Euphausiacea was great; in the warm years the number ofOithona simiZis increased and that one of juvenile euphausiids reduced (Fig.2).

The differences in plankton age composition in different flows of Atlantic watersbecause of the lateness of development periods in the more northward areas weremore significant.

During all the years of our investigations copepodites of C.finmarhicus I-III stages(Fig.3 ) prevailed in the surface layer plankton everywhere. But in cold 1979,when water temperature anomaly was negative, but rapidly reduced from winterminimum (-1.5”C) to 0.2OC towards late summer, the number of juveniles wasgreat all along the Kola Meridian Section and the peak was at the north stationsof the section, in the waters of the North Cape Current northern branch (74”N)(Tereshchenko, 1999). The similar picture was kept in the following cold years -1980, 1981. A different situation was observed in warm 1983 and 1984 - thenumber of Calanus juveniles was greater at the southern stations, i.e. in thewaters of the North Cape Current coastal and main branches (70-72”N), whenwarm water masses predominated in the area of the Kola Meridian Section. Forthis, the number of older individuals was noticeably less than in the cold years.

Obviously, year-to-year quantitative differences and latitude trends in distribution ofCalanus juveniles at I-III stages are well-explained by different growth periods.Delayed growth in cold years resulted in growing individuals staying too long in

3

the surface layers, especially, at the north stations, early growth in warm years -in early descending of growing year-class to the lower water layers and, hence,rapid depletion of the upper ones . By the way, the fact, that the number of olderindividuals was considerably more in late May, than in the warm years, indicatedthis. Consequently, mean plankton biomass in the Kola Section, containing threewater flows, reflects summary conditions of spring-summer growth, but does notconnect with water temperature at the certain moment.

Long-term series of May-June plankton biomass averaged by the section shows thefluctuations within the limits of SO-600 mg/m3 (Fig.4). Such great amplitude wasobserved in the 60s and mid-80s, but during the prolonged period of 1967-1984the biomass level was enough stable, and its variations did not exceed80-250 mg/m3. I t would appear reasonable that both system variations in biotaunder the influence of abiotic conditions and the change of biotic press onplankton might be the reasons of those fluctuations. The integral index of thefirst one are water temperature fluctuations, of the second one - abundance of mainconsumers -juvenile cods and capelin (Drobysheva, 1990). Since the boreal speciesC.finmarchicus was the main component of plankton community in the areasurveyed, it was natural to expect synchronous fluctuations of temperature andbiomass . However, the analysis of long-term fluctuations of plankton summerbiomass in the Kola Meridian Section revealed four periods of different biomasscorrelation with water temperature (see Fig.4): A and C - negative correlationwas accompanied by anomalous biomass leaps (from 50 to 600 mg/m3); B(asynchronous) and D - positive (synchronous) correlation was characterized bystable interannual producing at the mean level of biotic potential - 150-200mglm3.

Evidently, the mechanism of forming plankton community was different in thoseperiods, i.e. there was a change of leading factor.

Asynchronous stages coincided with abrupt reduction in the Barents Sea fishabundance as a result of their intensive fishing: in 1957 the stock of codsdecreased to 2.0 mill. t under 4.5 mi1l.t in the previous years, in 1987 capelinstock was reduced to 0.09 mi1l.t under the mean annual value of 5.3 mil1.t in theprevious ten years (ICES, 1999). Plankton and C.finmarchicus population, inthe first place, rapidly responded to the slackening of biotic press by surplussurvival (Drobysheva, Dolgov, Nesterova, 1991; Orlova, Matishev , 1993).H. Skjoldal drew the same conclusions (Skjoldal at all, 1991). Against this totalbiological background, which is the similar for all the zoogeographical groups, theimpact of hydrodynamic conditions was veiled., as the biotic factor was moreeffective regulator of plankton production level.

Synchronous periods coincided with high and relatively stable abundance of fishes,and, hence, with more even press of grazing. It caused stable low level ofbiomass, on the background of which the effect of Atlantic waters advection wasevident.

Ultimately, the character of annual variations of plankton biomass was the following:

1 Biomass correlation character and water temperature varied from time to time.

2.

3.

4

In the periods of direct dependence the level of mean biomass was low(150 mg/m3) and annual fluctuations did not exceed the increase in 2-3 times ;when the dependence was reverse, the mean value of biomass was two timeshigher (300 mg/m3 ) and annual fluctuations were increased in eight times.

Synchronous fluctuations of plankton temperature and biomass were observedin the periods of even fish-consumer press; while the asynchronous ones - inthe years of anomalous fluctuations of fish stock.

Therefore, temperature background provides relatively stable plankton communityfunctioning at the level of natural biological potential according to zoogeographicalstatus of species predominating; abrupt biotic disturbances change reservoirecosystem connections, on principle, therefore, become the main reason ofextreme fluctuations of plankton abundance in the Barents Sea.

5

REFERENCES

ANON., 1995. Dynamics of abundance and distribution of mass plankton groupsfrom the Barents Sea (Calanus, Euphausiaceu), in 1980-1995 as a factor of fishfood supply. Report on PINRO research work (Conclusion) ; Leader -S.S.Drobysheva. Subject 1, Section 1.33. Murmansk. 1995. 23~. (in Russian)

ANON., 2000. Report of the Arctic Fisheries Working Group. ICES C.M.,2000/ACFM: 3;68 pp.

BOGOROV, V.G. 1941. Biological seasons in plankton from different seas. DANSSSR. 1941. 31. N 4, p.403-406 (in Russian)

CHEREMISINA, V.T. 1948. On the zoogeography of the Barents Sea. TrJMBS.1948. P.293-298 (in Russian)

DERYUGIN, K.A. 1915. Fauna of the Kola Bay and conditions of its existence.SPb: Zap.SPb AN, Ser. 18. 1915. 340~. (in Russian)

DOBROVOLSKY, A.D. 1961 On determining water masses. Okeanologiya. 1961.Vol. 1, p.12-24 (in Russian)

DROBYSHEVA, S.S. 1990. Trophic relations of main ecological components inthe Barents Sea biota. Sel. papers : Food resources and relations of fishes in theNorth Atlantic. Murmansk, PINRO. 1990. p. lo-23 (in Russian)

DROBYSHEVA, S.S., NESTEROVA, V.N., NESVETOVA, G.I., RYZHOV, V.V.and A.I.CHEPURNOV. 1988. Division of the Barents Sea in view of primary andplankton production formation type. ICES, C.M. 1988/ L:7/ , p.l-5

DROBYSHEVA, S.S., DOLGOV, A.V. and V.N.NESTEROVA. 1991. Influenceof food supply of the Lofoten-Barents Sea Cod on its population status in the 80s.ICES C.M.l991/G:21, 1 Ip.

FILATOVA, Z.A. 1938. Quantitative assessment of bottom fauna in the south-western Barents Sea . Trudy PINRO. 1938. Issue 7, p.28-49 (in Russian)

HOFSTEN, N. 1916. Die Decapoden Crustaceen des Eisfjords. Zool.Erg. der Sved.Exped. nach Spitsbergen, 1908-l 9 16. Ibid.7. p. l-5

KUDLO, B.P. 1961. Some data on water exchange between the Barents andNorwegian Seas. Trudy PINRO. 1961. Issue 64. p.33-64 (in Russian)

KUDLO, B.P. and A.O.SHPAlKHER. 1979. Present-day variations of watertemperature in the Barents and Norwegian Seas. Trudy PINRO. 1979. Issue 34.p. 149-157 (in Russian)

MUKHIN, A..I... 1975. Thermic condition of waters in the southern Barents Seain 1948-1973. Trudy PINRO. 1975. Issue 35. p-71-83 (in Russian)

6

ORLOVA, E.L. and G.G.MATISHEV. 1993. Structural and functional role of codin the Barents Sea ecosystem. Apatity: Kola Scientific Center of RussianAcademy of Science. 1993. 162 p. (in Russian)

SKJOLDAL, V.E. 1991. Plankton in relation to climate and fish in the Barents Sea :events during the 1980s . The Symposium on Hydrographical Variability in theICES area, 1980-1989/ Mariekamp, Aland Isls, Finland, 5-7 June 1991. ICES -Copenhagen, 1991.20 pp.

TANTSURA, A.I. 1959. On seasonal variations of the Barents Sea currents. TrudyPlNRO. 1959. No.1 1. p. 35-53 (in Russian)

TERESHCHENKO, V.V. 1999. Hydrometeorological conditions in the Barents Seain 1985-1998. Murmansk: PINRO Press, 1999. 176 p. (in Russian)

YASHNOV, V.A. 1939. Planktonic productivity in the south-western Barents Sea.Trudy PINRO. 1939. p.201-218 (inRussian)

ZENKEVICH, L.A. 1963. Biology of seas in the USSR. M.-L.: AN SSSR. 1963.739 p. (in Russian)

~; 1') ~

vict:::J

(?)

,~~,: :."'"

780/ ,// /

/// //

// ////

////530/////////

//// ..'...//

//

~

.J- ~7.!.. o, I .-;:- I-"-::".:

-~-:>.'I .~

r cV:.-'\)-::

~

z

:".:~./~l"~

700

(),..~,

SO'400300

20.

iOO

1/ / 14I / '" J~~~2gi

Fig.! Chart of seasonal shift of "red Calanus" (IV-V stage s) in the Barents Sea

area

Legend: l -location of zone in May; 2 -in June; 3 -in July; 4 -in August.Figures in the chart mean maximum summer biomass in proper area of the

Barents Sea.

/:°/ ."" ./ / "", ,1.

r;:;]Il-t

a-:Q)-.5).O-O-.roQ)

Cij'

DO;=to'

3":JaJ

~.~.Cl?

æ-oCl>roc:c-o()tl)

Q)::Jc:Cl>

roO"::Jco~c:Cl>

~()Q)ro:Jc:cn~:J3Q)-,o::Jo'Ccn

8

)-'

<.D<.Dt\.J

)-'

c.oc.o)-'

~tO00tO

<D~<D

~(O

~

9

~~

(]Q~o~-In,~o3~--t(')O'"(5'C~

n-I

('J--P-4~ ,

NI

('J,~::j

3~...,(')O'"n'cV)

(')-<I

(')-<.

~

-<~-,

~~

'<t

~~:3~-.:3

~p)..,3----\,O00w..\,O00.f::.."-"p):3o..(")o-o..---..-\,O...J\,O

"-\O00o'-'"<~~-tV).

1"T'j_.~w

>-~~Cl>.-to

2(').-toC""1~oI-+)

(JE..~~cCl>

~~3~""1(')o-o'~

"Oo"Oc-~o'o~.-to=r~Cl>.-to

~.o~JA.oI-+)

.-.-~o-

~

~~-,-,O--.~~-.;(Z)~(').-to

o'~

~

10

Mean biomass of Calanus in 50-O m/layer, mg/cubic meter

.-.N (..> ~ U1 O) ---Jo o o o o o oo o o o o o o

roooo

1959

1960

1961

1962

1963

1964

1965

1966

1967

1968

1969

1970

1971

1972

1973

1974

1975

1976

1977

1978

1979

1980

1981

1982

1983

1984

1985

1986

1987

1988

1989

1990

1991

1992

1993

Q=4

~Q-=~~..,Q;;.=00~'"-o'=

~

-

C]to-o'3tl)C/JC/J

+ro3~

Q3

E"-.co

"""'-C')

o

(,) (,) ~ .l:.'0 -(.71 "o "U'

Mean annua I water temperature on" Kola Meridian" Section in 200. O m/layer, C o

U1"o/\J-(1'

~(jQ'~>.(t'J.,=

crQt'J

=o-==Co==t')t'J

Q~(j~~=cC-"

~==~.,t')=-?)'c(IJ

;-'Q=-=-t'J

'=~.,t'J=-(IJ

(IJt'J===Co

~~-t'J.,-t'J

3'Ot'J.,~-c.,t'J