Not to be cited without rior reference to the authors

International Council for theExploration of the Sea

C.M. 19931L:53Biological Oceanography Commitee

Session 0

VARIABILITY OF PHYTOPLANKTON BIOMASS AND PRIMARY PRODUCfIVITYIN THE SHELF WATERS OF TUE UPWELLING AREA

OF N-NW SPAIN

by

Antonio Bode1, Benita Casas1

, Emilio Fernandez2, Emilio Maraf16n3

, Pablo Serref and Manuel Varela1

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3

Instituto Espanol de Oceanografia. Apdo 130. E15080-La Coruna. Spain.Plymouth Marine Laboratory. West Hoe. PLI 3DH. Plymouth. England.Unidad de Ecologia. Dept. de Biologia de Organismos y Sistemas. Universidad de Oviedo.E33005-0viedo. Spain.

SUMMARY

Chlorophyll-a and primary productivity on the euphotie zone of the N-NW Spanish shelfwas studiedin 125 stations between 1984 and 1992. Three geographie areas (Cantabrian Sea, Rias Altas and RiasBajas), three batimetric ranges (20 to 60 m, 60 to 150 m and stations deeper than 200 m), and fourseasonal periods (summer upwelling, spring and fall blooms, summer stratification and winter mixing)were considered.

One of the major sources of variability of chlorophyll and production data was seasonaJ, withequivalent mean and maximum vaJues during bloom and summer upwelling periods. AverageehJorophyll-a eoneentrations approximately doubled in every step of the increasing produetivitysequenee: winter mixing - summer stratification - high produetivity (upwelling and bloom) periods.Primary production rates increased only 60% in the described sequence. Mean (:t:sd) values ofchlorophyll-a and primary production rates during the high produetivity periods were 59.7 :t: 39.5 mgChJ-a m-2 and 86.9 :t: 44.0 mg C m-2 h-1, respeetively.

Significant differenees in both chJorophyll and produetivity resulted between geographie areas in mostseasons. Only 27 stations showed effects of the summer upwelling that affected coastal areas in theCantabrian Sea and Rias Bajas shelf, but also shelf-break stations in the Rias Altas area. Tbe RiasBaixas area resulted with lower chlorophyll than both the Rias Altas and the Cantabrian Sea areasduring blooms, but higher during upwelling events. On the contrary, primary production rates werehigher in the Rias Baixas area during bloom periods. Mid-shelf areas showed the highest chlorophyllconcentrations during high productivity seasons, probably due to the existenee of various fronts in allgeographie zones considered.

Tbe estimated phytoplankton growth rates were comparable to those of other coastal upwellingsystems, with average values lower than maximum potential growth rates. Doubling rates for upwellingand stratifieation periods in the northern and Rias Altas shelf were equivalent, despite larger biomassaccumulations during upwelling events. Low turnover rates of the existing biomass in the Rias Bajasshelf during upwelling suggests that phytoplankton exported from the highly productive riasaecumulates near shore, and that 'in situ' production is of less importance.

1

INTRODUCTION

The seasonal upwelling system of the N and W Spanish shelf is considered an important source ofinorganic nu trients for primary produetion in that area (Blanton el aL, 1984; Varela, 1992). Cold,nutrient-rich deep waters have been detected near surface in discrete observations through the periodbetween March and Oetober, especially in the north-western shelf (Fraga, 1981, Fraga et a1., 1982,Rios et al., 1987, Varela and Costas, 1987, Varela et a1. , 1987a, b, 1988, 1991, Valdes et al., 1991).Ob ervations of upwelling events for the northern shelf (Cantabrian Sea, Southern Bay of Biscay) aremore scarce (Dickson and Hughes, 1981, Rios et al., 1987, Botas et al., 1990), and suggest that in thisarea the vertical advection of deep waler is related 10 the intensity of the upwelling in Ihe NW shelf,where lower surface temperatures ocurred.

During the thermal stratification period of the summer (May to September), this upwelling modifiesthe vertical structure of the water column, affecting di tributions of phytoplankton in relation to thetemperature and nutrient gradients (Varela et a1., 1987a, b, 1991, Botas et a1. , 1990). In contrast,upwelling events during the spring and autumn are influenced by the local circulation patterns causedby poleward currents flowing parallel to the shelf-break (Frouin et al., 1990). These currents can havea great influence on the development of phytoplankton blooms that normally occur in temperate coastalseas, as reported for the Cantabrian coast (Botas et al., 1988, Bode et al., 1990, Fernandez et aL, 1991,1993).

Coastal waters of NW Spain receive important contributions of exported nutrients and organic matterproduced in the estuarine rias (Tenore et a1., 1982, Lopez-Jamar et a1., 1992). Biological productivityin the rias is enhanced by the combined effects of nutrient-rich water entering from the sea duringupwelling events and local circulation (eg. Tenore et al., 1982, Blanton et al., 1984, Figueiras et al.,1985). Primary productivity of the rias was well studied, particular1y in relation to intense musseIaquaculture (eg. Varela et al., 1984 and references therein). However, there are far less data onphytoplankton productivity and biomass in the open shelf areas (eg. Varela, 1992).

The objectives of this paper are:

1) To summarize the existing information on simultaneous measurements of primary productivity andbiomass in the area affected by the coastal upwelling.

2) To study seasonal and spatial variability in chlorophyll-biomass and phytoplankton carbonproduction in relation to specific questions: i Is the southern part of the area is mOfl~ productivebecause the additional enrichrnent of the rias outflow ? i How different are the values obtained duringthe high production seasons in the low-intensity upwelling area of the Cantabrian Sea and thoseobtained in the western shelf ?

3) To compare primary production and phytoplankton growth rates from high production periods indiverse areas of the N-NW Spanish shelf and other coastal upwelling areas.

METHODS

Figure 1 shows the positions of the stations in whicb phytoplankton biomass and primary productionwere studied between 1984 and 1992. Details of sampling and hydrographic data sources are Iisted inTable 1. Sampies were grouped according to their geographical procedence: 'Cantabrian Sea', 'RiasAlIas' and 'Rias Baixas', and the deplh of the station. Three batimetric ranges were considered: 'CoastaJ'

(20 to 60 rn depth), 'Mid-shelf (60 to 150 rn) and 'Off-shelf (stations deeper than 200 rn).

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Tempcraturc and salinity werc measured .with CfD probes (cruises in the western shelf) or aninduction salinometer (cruiscs in thc Ointabrian Seal. Dissolved mitrient concentrations (nitrate andphosphate) ~'cre dctcrmined with an autoanalyscr (Gras~hoffet al., 1983). Photosynthetically availablcradiation(PAR) was mcasüred witli a submcrsiblc quantum·sensor. Chlorophyll-aconcentrations wercmeasured fluorometrically on 90% acetone extracts of particulate material (parsans et al.; 1984).Primary production rates werc determined at 5 t~ 7 selected depths, using 'in situ'. or'in situ' siniulatedcOnditions (fable 1) on duplicate 100 to 250 mIsamples inoculated with NaH14C03. Average C-14additions were 4 IlCi 14C in the ~'estern shelf cruises and 2 to 10 IlCi 14C in the Cantabrian Seacruises. Simulated 'in situ' incubations were carried out using neutral density screens to simulate 5 to7 light levels, corresponding to those received at the sampling depths. Incubations were made aroundnoon and lasted from 2 to 4 h. Filters employed for chloropyll and productivity determinations werelisted in Table 1. Corrections for dark uptake of C \\'ere made only in the western shelf cruises. ,AllchlorophyJl and production valucs v,'crc intcgratcd i.ri thc cuphotic zone.

Hydrographie and chlorophyIi data were used to c1assify. sampies in definite seasonai oceanographieperiods, following thc information available in thc area (Fraga et al., 1982, Rios et al., 1987, Botaset al., 1988, Valdes et al., 1991, Varela, 1992). 'Bloom' samplcs c.Orrespond to stations studied during

•the spring and auturilO that showed mean chlorophyll-a concentrations bigher than 1 Ilg 1-1 in mostof thc cuphoiic zone arid wcak vertical water density gradients. 'Up~;elling' sampies are summer c3sesthat showed cold «14°C) and nutrient-rich (>5 IlMN-N03-1-t, >O.4i.tM P-PO/-). All sampies fromthc sl.nniner that did not show any characteristie of upwelling w~e c1assified in the group narned'Stratification'. Finally, stations that showcd a ihoroughiyniixed ~:ner column, includirig some sampiesof spring and autumn with low chlorophyll conccntrations, '1.-e~ed~ssified as 'Winter'.

w.......

Carbon pdmary produetion to biomass ratios werc estimated' for .the main periods and' areas usirigaverage chlorophylland pdmary productionvalues. Chlorophyll':':i was eonverted to carbon using amean factor of.o::1ÖO IlC (Ilg Chl-at 1. Minimum änd maximum, range values"'were computed .consideririg ratiÖSY"of 50 lmd 200 Ilg C (Ilg ChI-ar1, respeetively. These conversions are Iikely toprodticc conservative estimates of phytoplankton gfoMh rates i.ri upwelling areas (Brown et 31., 1991),giveri thc large variations in the. carbon to chlorophyll ralios oe natural phytoplankton (eg. Banse,1977). Tbe measured hourly carbon fixation rates were extrapolated to daily rates by assuming aneffective daylcnght of10 h in summer 'Upwelling' and 'Stratification' periods, 8 h during spring andauturrin 'B1oom' peri~ds, and 6 hinthe 'Winter' period. .. ~i'

.:--:Signiflcatlon of ili~'differences bctween spatial .lnd temporal classificätions were test~d usirig analysisof variance (anöva) methods (Sok31 and Rohlf, 1981) using logarithmie transformations of chlorophylland production v~l1ues. Due to. the lack of data in certain combinätions of periods and areas a fullnested anova dessign to obtain a complete partition of variance in seasonal, geographical aridbatimetric zone components was not possible. We uscd single dassification anova to test seasonaldiffcrences, and ncstcd anovas of spatial glOUPS within scasonal j>eriods mthc' snidy of spatialeomponents of variancc. . .

. - ~ .RESULTS AND DISCUSSION

T~por~illiiatio~

Seasonal variations are a major eon1ponent of variability in chlorophyll-a and primary production ratesthrough the area. Figure 2 displays mean values calculated for the selccted periods; indicating that the'a priori' c1assification of sampies was appropiaie (F = 28.94, p<O.OOOI). Multiple comparisons .between means revealed that differences in both chlorophyll and prOduetion between 'Bloom' and'Upwelling' periods were not significantly different (Studerit-Neuinari-Keuls test, p>O.05), but there

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were clear differenees in all other groups. Average ehJorophyll concentrations of the 'Stratification'period was approximately twice the value of the 'Winter' period, and half of the mean value of thehigh produetivity periods ('Bloom' and 'Upwelling'). Mean (:tsd) values of chJorophyll-a and primaryproduetion rate during the high produetivity periods were 59.7 :t 39.5 mg Chl-a m-2 and 86.9 :t 44.0mg C m-2 h-1, respeetively. These values are within the range obtained in other upwelling areas, likeBenguela (40 - 340 !lg C m-2 h-I

, Shannon and Field, 1975, Estrada and Marrase, 1987, Brown et al.,1991), but lower than those cited in other systems (eg. up to 1000!lg C m-2 h-I in the Peru upwelling,Ryther et al., 1971).

Upwelling events are knO'N'O to be very dynamie features, changing water-column properties andplankton communities during short time scales (Blaseo et a1., 1981). This is indieated by the fact that,despite most of the crui es employed in this study were made during the upwelling season, only asmall fraetion of sampIe (27 of 125) showed clear upwelling charaeteristics. Productivity and biomassis generally low during phases of intense water-mixing, when nutrient coneentrations are high, andinereases in phases or areas of moderate turbulence (Margalef and Estrada, 1981). We studiedvariations within the 'Upwelling' sampIes by means of a distinetion of two phases: 'Initial', with highnutrient and low chlorophyll concenlrations, and 'Final', with the eonverse eonditions. Mean (:tsd)values of ehlorophyll-a for 'Initial' and 'Final' periods were 50.99 :t 28.46 Ilg Chl-a I-I (n=10) and69.95 :t 43.85 !l& Chl-a t l (n=17), respeetively. Primary produetion rates were 90.79 :t 44.57 Ilg C •I-I h- I during the 'Initial' phases and 82.21 :t 42.41 !lg C I-I h- I during 'Final' upwelling phases.However, no significant differences between two phases resulted for either ehlorophyll-a nor primaryproduetion beeause of high variances (Mann-Whitney test, p>0.05). The relatively low number ofupwelling cases used in this study diffieults any attemp to study patterns of internal variation. Thereare some evidenees of day-to-day variations in planktonie biomass and produetivity assoeiated toupwelling and downwelling phenomena in this area (Varela et al., 1991). This feature deserves muehlarger attention in future studies, beeause variations in both physieal and biological characteristics inshort time and space scales may have important implications on the fate of the phytoplanktoniebiomass produced by upwelling events. One major quest ion in relation to this subject is thedetermination of the capability of this upwelling to export organic matter out of the euphotic zone, andits variations in the different geographie areas.

S atial ~'ariations

The geographical location of sampling was an important contribution to added variance in bothchlorophyll and primary production values. Figure 3 shows the variance partition of both variables inseasonal ('Period') and geographie ('Area') components using a nested anova, with the 'Area' componentas the nested faetor. SampIes for the winter period were excluded because there was no data for theRias Baixas area. Seasonality was the main source of variation in chlorophylJ-a values whilegeographie loeation was responsible for near 90 % of the variations in primary produetion rates. Themean values of Table 2 show that the Rias Baixas area resulted with higher produetion rates in theRias Baixas area during 'Bloom' periods but also with the lowest rates during the 'Stratifieation' period.Tbe Rias Altas area had intermediate produetion rates in all seasons, but mean ehlorophyll-aconeentrations resulted higher than in the other areas during 'Bloom' and 'Stratification' periods.

Another major source of variability in chlorophyll and primary production values was the depth of thestudied stations and their position relative to the coast. Apart from the evident seasonal variability,there was a significant component of added variance due to the 'Zone' component when data form allgeographie areas were combined (fable 3). Table 4 displays mean values for a11 combinations ofpariods and zones, indicating higher chlorophyll concentrations in the mid-shelf zone during highproduction periods ('Bloom' and 'Upwelling'). Chlorophyll concentrations in the outer shelf zone weregenerally lower than in stations close to the coast. However, the pattern exhibited by primary

- - --- -------------------.: ~ •.'~ \f,"; ~:r.::.':....

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production rates rcsullcd more variable, with higher ralc~ near the coast during 'BIoom' periods andin the mid-shelf zone in all other seasoris. .

..,' ," 'oo ~ ~" ''':'''' ,'> ,:".: "," ',.o ,'":/:"t;·. :,' '. "Mld-shelf areas are a place where a vanety of fronts can be expected (eg. Holhgan, 1981), and theeharacteristics and biological implications of some. of them iri thc Cantabrian Sea had been already _.deseribed (Botas el a1., 1988, Bodc ct a1., 1990, Femandez et a1., 1991~ 1993). Large, and possiblypermanent frontal systems, had bcen reported for the bourida:ries between the. lhrce geographie arcaseonsidered. Fraga ct a1 (1982) and Rios et a1. (i992) reeognized a distinet off-shore surfacecireulation arid a pemianent subsurfaee front off Cape Finistcrre, between the Rias Altas and the RiasBaixas areas. Similarly, there are evidenees of similai fronts off Cape Ortegal, betweeri the Rias Atltasiuea and the Cantabrian Sea (Diai deI Rio cf a1., 1992). These fronts can determine the input ofstirface waters from thc Cenlral Atlantic into the southem Bay of Biseay (Pingree and Le Cann, 1990,Pingree, 1993). Howevei', the biological implications of such fronts in thc NW coast of Spain havebeen scarcely studied (eg. Varela et a1., 1991).'

Doubiirig rates of the existirig biomass may allow for eomparison betwcen different upwelling systems(eg. Brown et a1., 1991). The values calculated with our data indicated that the areas of higherphytoplanktori gro~1h vary seasonally (Table 5). The highest rates werc found in the Rias Baixas areadtiring the 'BIoam' period, but high values were fourid in the Cantabrian Sea arid Rias Altas areaduririg 'Upwelling' and 'Stratification' periods, when phytoplankton growth iri the Rias Baixas area wasrelatively slow. Values for the Cantabrian Sea resulted in general higher than those of the western partof the area, but methodological differences may account for part of this discrepancy, since nosubstraction of dark bottle counts have been applied to the Cantabrian Sea data. Femandez and Bode(in press) have shown that dark bottle substraction may severely underestiniate primary productionrates during periods of slow gro~1h, like the 'Winter' period.

Average gro~1h rates calc~lated for our mean doubling rates during the 'Upwelling' period resultedlower than the expected maximum grO~1h rates calculated with the equation of Eppley (1972):

10g10 Q=0.0275 T - 0.070

where Q is the doubling time (inverse of growth rate) expresscd as days neeessary to double theexisting biomass, andT is the ambient (water) temperature. The temperature of surface waters irithestudied area ranged between 13 arid 20 oe and the corresponding maximum phytoplankton growthrates will be 0.51 and 0.33 doublirigs day·l, respeetivelY. With a mean temperature of surface waterof 15 oe during upwelling events, the expeeted growth rate will be 0.45 day·I, ie. phytoplanktonbiomass will double every 2.2 days. The estimated rates during upwelling events in our studyarearange from 0.47 day·l (biomass double every 2.11 days) iri the Cantabriari Sea, to 0.05 day·l (biomass .double every, 19.2 days) inthe Rias Baixas area. Low biomass tiunover rates in the Rias Baixas areaduring upwelling events in the summer are in agi-eement with the hytpothesis that coastal areas in thisregion reecive important mputs of phytoplankton and partieulate organic matter from the nearby rias(Estrada, 1984). The high primary produetion rates inside these shallow, proteeted environments(Varela et aL, 1984) is effectively exported to coastal areas, where loeal cireulaiion patterns maydetermine its accumulation near the coast or further exPort to other shelf areas (Lopez-Jamar et a1.,1992). Our data suggest that 'in situ' production in coastal areas near the Rias Baixas is lo~' comparedto production iri other shelf areas, despite of the additional nutrients regenerated inside the rias than'can be released with the outflow (Tenore ct a1., 1982, Lopez-Jamar et a1.~ 1992) arid 'iri situ'regeneration (Mouriiio et aL, 1984, IgJesias et aL, 1984).

The comparison of phytoplankton productivity valuc computed for different time-scales reveals thatthese calculations may have an important effect in the estimation of the impact of the high productivityevents in thc pelagic ecosystem. Despite hourly production rates for 'Bloom' and 'Upwelling' periodswere comparable, the extrapolation to daily rates, which takes into account the effective daylenght,indicates that upwelling episodes produced during summer will produce higher biomasses. The factthat chlorophyll concentrations resulted similar for 'Bloom' and 'Upwelling' periods may be explainedby a elose-coupling between primary producers and consumers or, altematively, by hidrographicmechanisms favouring sedimentation of recently produced organic material during summer upwellingevents. Relatively high mesozooplankton biomasses have been reported in the area during periods ofweak upwelling (Valdes et aL, 1991, Varela et aL, 1991). In addition, microbial-Ioop consumers arecapable to remove a large fraction of the daily primary production in an upwelling event of the RiasAltas area (Bode and Varela, in press), and there are examples of rapid phytoplankton degradationthrough bacteria in other bloom areas (eg. Newell and LinJey, 1984). On the other hand, there arereports of downwelling occurring shortly after the maximum productivity period during upwellingevents (Blanton et aL, 1984, Varela et aL, 1991). The rapid sinking of surface water may enhance theeffective sedimentation of the produced material out of the euphotic zone (Varela et aL, 1991) to largeareas of the bottom (Lopez-Jamar et aL, 1992). Probably both mechanisms occurred simultaneously.

Another interesting feature of the estimations displayed in Table 5 is that growth rates computed for •the 'Stratification' period resulted sometimes comparable or higher than those of 'Upwelling' and'Bloom' periods. Production maxima and chlorophyll accumulation in subsurface layers is one of themajor characteristics of stratified water columns in most seas (CulJen, 1982, Estrada, 1985, Dortch,1987, Fernandez and Bode, 1991). Physiological indicators and 'in situ' measures of phytoplanktonproduction indicate that in the Cantabrian Sea these subsurface chlorophyll maxima are produced byactive growth (Fernandez and Bode, 1991). Since sedimentation of particles below the euphotic zonein these periods is expected to be reduced, because of the large water density gradient near thepicnocline, 'in situ' decomposition of organic matter by microplankton appears as a likely explanationof the low phytoplankton biomass. There are evidences that, at least in subsurface chlorophyll maximainside the rias, elose coupling of microheterotrophs and phytoplankton may occur during summer(Figueiras and Pazos, 1991).

CONCLUSIONS

3. The estimated phytoplankton growth rates were comparable to those of other coastal upwellingsystems, with average values lower than maximum potential growth rates. Doubling rates forupwelling and stratification periods in the northern and Rias Altas shelf were equivalent,despite targer biomass accumuJations during upwelling events. Low turnover rates of tbeexisting biomass in the Rias Bajas shelf during upwelling suggests that phytoplankton exported

•Seasonality resulted a major factor of variation of chlorophyll concentrations and prirnaryproduction rates of the shelf area of NW Spain. Shorter time scales are likely to be veryimportant during high production periods, but more data are needed to demonstrate patternsin both parameters during upwelling events.

1.

2. There was a significant interaction between seasonal and spatial variability in chlorophyll andproduction values. The Rias Baixas area resulted with lower chlorophyll than both the RiasAltas and the Cantabrian Sea areas during blooms, but higher during upwelling events. On thecontrary, primary production rates were higher in the Rias Baixas area during bloom periods.Mid-shelf areas showed the highest chlorophyll concentrations during high produetivityseasons, probably due to the existence of various fronts in alJ geographie zones considered.

~ .; I '. ~.' ,f. ..!t,' ~ , ,

from the highly produetive rias aeeumulatcs ncar shore, and that 'in situ' produciion is of less .. importanee. .

1! .,io '.; • ~ .4: ".' I ::. ,,'. ~ ..

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ACKNOWLEDGEMENTS

We are indcbted to the various scientists, teehnicians and ship-erews that collaboratcd in thc .mcasurcments taken at sea and in laboratory analysis during a11 these years. R Carballo and A Botas;providcd hydrographie and ehcmical data and J. Lorcnzo assisted with sampling and graph drawing.BREOGAN cruises were funded by the Joint Spanish-USA Program FOG CCA83/023 and theInstituto Espaiiol de Oceanografia (IEO). COCACE cruises were funded by Hidroeleetrica deICantabrico S.A and the Universidad de Oviedo. ASFLOR cruises were supported by CICYT grantMAR88-0408 to the Universidad de Oviedo. The eontinued sampling at La Coruiia and Asturiastranseets is supported by IEO Program 1010.

REFERENCES

Anad6n, R, E. Femandez, A Botas, A Bode, P. Serret, J.L. Aeuna, J. Cabal, 1. Sostres and F.Alvarez-Marques.-1991. Datos basicos de la campana "ASFLOR }". Biobas. Rev. Biol. Univ. Oviedo.5:1-36.

Banse, K.-1977. Determinig the carbon-to-eWorophyll ratio of natural phytoplankton. Mar. Biol.41:199-212.

Blanton, J.O., L.P. Atkinson, F. Femandez de Castillejo and A Lavin Montero.-1984. CoastalupwelJing off the Rias Bajas, Galicia, Northwest Spain. I. Hydrographie studies. Rapp. P-V. Reun.Cons. Int. Exnlor. Mer 183:79-90.

Blasco, D., M. Estrada and B.H. Jones.-1981. Short time variability of phytoplankton populations inupwelling regions. Tbe example of northwest Africa. In: Coastal Upwelling. F.A Richards (ed.).American Geophysical Union. Washington D.C. 339-347. .

Bode, A, E. Femandez, A Botas and R Anad6n.-1990. Distribution arid composition of suspendedparticulate matter related to a shelf-break saline intrusion in the Cantabrian Sea (Bay of Biseay).Oceanol. Acta. 13(2):219-228.

Bode, A and M. Varela.-(in press). Planktonic carbon and nitrogen budgets for the N-NW Spanishshelf: The role of pelagic nutrient regeneration during upwelling events. Sei. Mar.

Botas, J.A, A Bode, E. Femandez and R. Anad6n.-1988. Descripci6n de una intrusion de agua deelevada salinidad en el Cantabrico Ceritral: distribuci6n de los nutrientes inorganicos y su relaci6n conel fitoplancton. Inv. Pesq, 52(4):559-572.

Botas, JA., E. Femandez, A Bode and R Anad6n.-1990. A persistent upwelling off the CentralCantabrian Coast (Bay of Biscay). Estuar. Coast. Shelf Sei. 30:185-199.

Botas, J.A., E. Femandez, A Bode, R Anad6n and E. Anad6n.-1989. Datos basicos de las eampaiias"COCACE". 1.- Hidrografia, nutrientes, fitoplancton y seston en el Cantabrico Central. Diobas. Rev.Biol.Univ. Oviedo. 1:1-80.

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Bro'-''11, P.c., S.J. Painting and K.L. Cochrane.-1991. Estimates of phytoplankton and bacterial biomasand production in the northern and southern Benguela ecosystems. S. Air. J. Mar. Sei. 11:537-564.

Cullen, U.-1982. The deep chlorophyll maximum: comparing vertical profiles of chlorophyll a. Can.J. Fish. Aqual. Sci. 39:791-803.

Diaz deI Rio, G., J. Alonso, MJ. Garcia Femandez, JM. Cabanas and J. Molinero.-1992. Estudiodinamieo de la plataforma continental deI norte de Galicia (Abril - Junio 1991). lnf. Tee. Inst. Esp.Oceanogr. 134:1-23.

Diekson, R.R. and D.G. Hughes. -1981. Satellite evidenees of mesoscale eddy aetivity over the Biseayabyssal plain. Oceanologica Acta. 4:43-46.

Dortch, Q.-1987. The biochemical composition of plankton in a subsurface chlorophyll maximum.Deep-Sea Res. 34:705-712.

Eppley, R.W.-1972. Temperature and phytoplanktongrowth in the sea. Fishery Bull .. Wash. 70:1063­1085.

Estrada, M.-1984. Phytoplankton distribution and composition off the coast of Galicia (northwest ofSpain). J. Plankton Res. 6(3):417-434.

Estrada, M. -1985. Primary production at the deep chlorophyll maximum in the western Mediterranean.In: Proceedin s of the 19th Euro ean Marine Biolo S m osium. P.E. Gibbs (ed.). Cambridge Univ.Press. 109-121.

Estrada, M. and C. Marrase.-1987. Phytoplankton biomass and productivity off the Namibian coast.S. Air. J. Mar. Sei. 5:347-356.

Fernandez, E. and Bode, A-1991. Seasonal patterns of primary production in the Central CantabrianSea (Bay of Biscay). Sci. Mac. 55(4):629-636.

Fernandez, E. and Bode, A-(in press). Seasonal patterns of dark carbon incorporation by naturalphytoplankton in the Central Cantabrian Sea (Bay of Biscay). P.S.Z.N.I.: Marine Ecology.

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Fernandez, E.; A Bode, A Botas and R. Anadon.-1991. Microplankton assemblages associated withsaline fronts during aspring bloom in the centraJ Cantabrian Sea: differences in trophic structure •between water bodies. J. Plankton Res. 13(6): 1239-1256.

Fernandez, E., J. Cabal, J.L. Acuna, A Bode, A. Botas and C. Garcia-Soto.-1993. Planktondistribution across a slope-current induced front in the southern Bay of Biscay. J. Plankton Res.15(6):619-641.

Figueiras, F.G. and Y. Pazos.-1991. Microplankton assemblages in three Rias Baixas (Vigo, Arousaand Muros, Spain) with a subsurface chlorophyll maximum: their relationships to hydrography. Mar.Ecol. Prog. Sero 76:219-233.

Figueiras, F.G., F.X. NielJ and M. Zapata.-1985. Hidrografia de la Ria de Pontevedra (NO de Espana)con mencion especial al banco de Placeres. lnvestigacion Pesq. 49:451-472.

•

• .',' ~ • ~ +. "

Fraga; F.-1981. Upwelling off the Galician Coast, Northwest Spain. In: Coastal I.!pwclling, F.A.Richards (cd.). pp. 176-182. Amcrican Geophysical Union. Washington, oe.

' .... , . . ..:,

Fraga, F.; C. Mourino and M. Manriqucz.-1982. Las masas'de 3gua en la costa dc Galicia: junio-octubre. Invest. Pcsg. Res. Exp. Cient. 10:55-77. .

Frouin, R., A. Fiuza, I. Arnbar and T.J. Boyd.-1990. Observations of a poleward surfacc eurrent offthc eoasts of Portugal and Spain during winter. J. Geaphysical Res. 95(Cl):679-691. .

Grasshoff, K., M. Ehrhardt and K. Krembling.-1983. Methods of seawater analysis. 2nd. Ed. VerlagChemie. Weinheim. 419 pp. .

Holligan, P.M.-1981. Biological implications of fronts on the northwest European continental shelf.Phi). Trans. R. Soc. Lond. A302:547-562.

Iglcsias, M.L., N. Gonzalez, J.M. Cabanas and T. Nunes.-1984. Condiciones oceanognificas deI asRias Bajas gallegas y de la plataforma ad)·acente. Cuadernos da Area de Ciencias Mariiias. 1:107-118.

Lopez-Jamar, E., RM. Cal; G. Gonzalez, R.B. Hanson, J. Rey, G. Santiago and K.R. Tenore.-1992.Upwelling and out\l:elling effects on the benthic regime of the continental shelf off Galicia, NW Spam.J. Mar. Res. 50:465-488.

Margalef, R. and M. Estrada.-1981. On upwelling, eutrophie lakes, the primitive biosphere, andbiological membranes. In: Coastal Upwelling. F.A. Riehards (ed.). Arnerican Geophysical Union.Washington D.C. 522-529.

Mouriiio, e., F. Fraga and F. Femandez.-1984. Hidrografia de la Ria de Vigo. 1979 - 1980.Cuadernos da Area de Ciencias Mariiias. 1:91-106.

Newell, RC. and E.A.S. Linley.-1984. Significance of microheterotrophs in the dccomposition ofphytoplankton: estimates of carbon and nitrogen 110w based on the biomass of plankton·communities.Mar. Ecol. PragT. Sero 16:105-119.

Parsons, T.R., Y. Maita and e.M. LalJi.-1984. A manual of chemical and biological methods forseawater analyses. Pergamon Press. Oxford, 173 pp.

Pingree, RD.-1993. Flow of surface waters to the west of the British Isles and in the Bay of Biscay.peep-Sea Res. 11. 40:369-388.

Pingree, RD. arid B. Le Cann.-1990. Structure, strenght and scasonality of the slope currcnts in theBay of Biscay region. J. Mar. Biot. Ass. U.K. 70:857-885.

Rios, A.F., F.F. Perez and F. Fraga.-1992. Water massesin the upper and middle North Atlantie Oceancast of thc Azores. Deep-Sca Res. 39:645-658.

Rios, A., F. Fraga, F.G. Figueiras, R Prego and F.F. Perez.-1987. Campafias oceanograficas "Asturias1,11, 111 y IV". Datos informativos Instituto Investigaciones Marinas. Vigo. 22:1-140.

Ryther, J.H., D.W. Menzel, E.M. Hurlbert, C.J. Lorenzen and N. Corwin.-1971. Tbc production andutilization of organic matter in the Peru coastal current. Investigaci6n Pesq. 35:43-59.

Shannon, L.V. and J.G. Field.-1985. Are fish stocks food-limited in the southem Benguela pelagiceeosystem ? MaL EcoJ. Pro . Ser. 22:7-19.

Sokal, R.R. and F.l. Rohlf.-1981. Biometry. The principles and practice of statistics in biologicalresearch. 2nd. ed. W.H. Freeman and Co., San Franeisco.

Tenore, K.R., L.F. Boyer, R.M. Cal, Corral, 1., C. Garcia-Fernandez, N. Gonzalez, E. Gonzalez­Gurriaran, R.B. Hanson, 1. Iglesias, M. Krom, E. Lopez-lamar, 1. McClain, M.M. Pamatmat, A. Perez,D.C. Rhoads, G. Santiago, 1. Tietjen, 1. Westrich and H.L. Windom.-1982. Coastal upwelJing in theRias Bajas, NW Spain: Contrasting the benthic regimes of the Rias de Arosa and de Muros. 1. Mar.Res. 40:701-772.

Valdes, L., MT. Alvarez-Ossorio, A. Lavin, M. Varela and R. CarbaUo.-1991. Cido anual deparametros hidrograficos, nutrientes y plancton en la plataforma eontinental de La Coruiia (NOEspaiia). Bol. Inst. Esp. Oceanogr. 7(1):91-138.

Varela, M.-1992. UpweUing and phytoplankton ecology m Galician (NW Spain) rias and shelfwaters.Bo\. Inst. Esp. Oceanogr. 8(1): 57-74.

Varela, M. and E. Costas.-1987. Distribucion deI tamaiio de las espeeies deI fitoplancton en un areade afloramiento. Inv. Pesq. 51:97-106.

Varela, M., G. Diaz deI Rio, M.T. Alvarez-Ossorio and E. Costas.-1991. Factors controllingphytoplankton size dass distribution in the upwelling area of the Galician continental shelf (NWSpain). Sei. Mar. 55:505-518.

Varela, M., 1.M. Fuentes, E. Penas and J.M. Cabanas.-1984. Producci6n primaria de las Rias Baixasde Galicia. Cuadernos da Area de Ciencias Mariiias. Seminario de Estudos Galegos. 1:173-182.

Vare1a, M., M.J. Campos, 1.M. Cabanas, F.F. Castillejo and G. Diaz dei Rio.-1987a. Composicion ydistribucion dei fitoplancton en 1a plataforma de Galicia durante la Campaiia Breogan 984 (septiembre1984). Bo\. Inst. Esp. Oceanogr. 4(1):95-106.

Varela, M., M.T. Alvarez-Ossorio, L. Valdes, R. Ca1, A. Miranda, G. Santiago y E. Costas.-1988.Partieion de la materia organica particulada en el area de afloramiento de la p1ataforma de Galicia (NOEspaiia) durante 1a Campaiia Breogan 684. Bol. Inst. Esp. Oceanogr. 5(1):97-108.

Varela, M., J.M. Cabanas, M.J. Campos, E. Penas, J. Sanchez, A. Larraiiaga, F.F. Castillejo and G.Diaz dei Rio. -1987b. Composici6n y distribucion deI fitoplancton en la p1ataforma de Galicia durantela Campaiia Breogan 684 (junio de 1984).Bo1. lnst. Esp. Oceanogr. 4(1):75-94.

•

Table 1

Cruises and methodological characteristics of data used in this study.

Cruise Dates Area* Filter** Filter** Incubation type ReferencesChl-a Prod.

BREOGAN-684 Jun 1984 RA,RB MO.8 MO.8 "in situ" Yarela et al. 1987b,l988BREOGAN-984 Sept 1984 RA,RB MO.8 MO.8 "in situ" Yarela et al. 1987aBREOGAN-785 Jul 1985 RA,RB MO.8 MO.8 "in situ" Yarela et al. 1991BREOGAN-486 Mar-Apr 1986 RA,RB MO.8 MO.8 "in situ" unpubl. dataCOCACE Jan-Dec 1987 CA GF/C MO.8 "in situ" Botas et aI. 1989ASFLOR-I Aug 1989 CA GF/F GF/F "in situ simul." Anad6netal.l991ASFLOR-1I Jul 1990 CA GF/F GFfF "in situ simul." unpubI. dataLa Coruna transect Jan 199I-Dec 1992 RA MO.8 MO.8 "in situ simuI." Yaldes et al. 1991 and unpubI. dataAsturias transect Aug 1991 CA GF/F GF/F "in situ simul." unpubI. data

I !' ' . .j,

"*CA: Cantabrian Sea area

:.:, ...

RA: Rias Altas areaRB: Rias Baixas area

**MO.8= Millipore cellulosa-acetate membrane filters 0,8 f-lm pore size.GFfC= Whatman GF/C glass fiber filters.GF/F= Whatman GF/F glass fiber filters.

l _

Table 2

Mean (± sd) chlorophyll-a (Chl-a, mg m-2) and production (Prod, mg m-2 h- I) values for

the different areas and oceanographic periods. Number of data points appear in brackets.

Chl-a

Area Bloom Upwelling Stratification Winter

Cantabrian 49.33± 19.29 4O.72±14.32 25.33± I0.85 15.64±7.52(7) (4) (27) (9)

Rias Altas 67.68±49.49 57.84±41 .86 37.55±24.44 15.64±3.80 •(13) (16) ( (5) (11)

Rias Baixas 32.84±10..50 87.11 ±34.04 35.53±20.45(4) (7) (12)

Production

Cantabrian 93.11±.5O.66 96.13±45.84 57.54±30.31 38.07±25.07(7) (4) (27) (9)

Rias Altas 77.43±43.80 80.17±46.86 56.00±34.47 17.29±11.87(13) (16) ( (5) (11)

Rias Baixas llO.75±43.65 91.18±33.54 41.48±25.57(4) (7) (12)

•

Table3

Summary of anova results for the effects of three batimetric zones ('Coastai', 'Mid-shelf and

'Off-shelf) within sampling periods ('8100m', 'Upwelling" 'Stratification' and 'Winter

mixing') on water column integrated chlorophyll-a (Chl-a) and production (Prod).

SS: sum of squares, DF: degrees of freedom, MS: Mean squares, E: MS-ratio, l!: probability

of Evalues. The error terms correspond to within cell variability. SS for the effects were

computed sequentially as they are listed below.

Variable Effect SS DF MS E

Chl-a Error 5.96 113 0.05Period 41.34 3 13.78 261.39 0.000Zone within period 55.42 8 6.93 131.40 0.000

:I:'~

Prod. Error 9.48 113 0.08Period 55.54 3 18.51 220.72 0.000Zone within period 70.14 8 8.77 140.53 0.000

Table4

Mean (± sd) chlorophyll-a (Chl-a. O1g 01-2) and production (Prod. O1g 01-2 h- 1) values for

three batimetric zones ('Coastai', 'Mid-shelf and 'Off-shelf) and oceanographic periods

('8100m'. 'Upwelling'. 'Stratification' and 'Winter mixing'). Number of data points

appear in brackets.

Coasta1

Mid-shelf

Off-shelf

Coasta1

Mid-shelf

Off-shelf

Chl-a

810001 Upwelling Stratification Winter

43.13±21.23 62.36±36.40 33.21 ±21.26 15.33±8.79(9) (17) (16) (5)

82.70±52.23 65.09±55.29 32.25± 19.39 15.17±4.19(9) (7) (14) (12)

37.35±12.33 60.76± 19.30 28.66±16.04 18.03±6.10(6) (3) (24) (3)

Production

97.83±53.13 83 .88±43.05 59.78±34.74 21.42±13.94(9) (17) (16) (5)

90.25±44.16 95.88±44.80 65.44±30.73 29.38±25.25(9) (7) (14) (12)

68.11 ±34.67 . 69.43±43.85 42.67±24.85 24.38±16.46(6) (3) (24) (3)

•

Table5

Estimates of phytoplankton growth rates for the studied area and periods using average

water column integrated values of chlorophyll-a and production. Values are in doublings

day-I (see methods section for details of calculations). Maximum and minimum estimates

appear in brackets.

Cantabrian

Rias Altas

Rias Baixas

Bloom Upwelling Stratification Winter

0.151 0.236 0.229 0.170(0.075-0.302) (0. 118-0.472) (0.114-0.457) (0.085-0.341 )

0.092 0.139 0.149 0.07(0.046-0.183) (0.069-0.277) (0.075-0.298) (0.039-0.155)

0.269 0.105 0.117(0.134-0.540) (0.052-0.209) (0.058-0.257)

Cantabrian Sca

+ O·10'"\1

•'- ....' i·· .~'.\ • ,"- --oe "• .',., 1.",-'- \ . .

• '. > •

••

200 m

,,

Rias Altas

. "

,,,,

\

••I,

I,\

\.',\

\

I( ....~,

I

'"/I\•I\

' .. -;',•'.

Rias Baixas

4ZON+

Figure 1.- Position of stations studied.

140~-----------------------,

120

c:: 100o

24 27

~ Chl-a (mg m 2)

o Prod (mg m 2h I)

(j:::l

"'0ocl:...oC":l,-..c::

U

80

60

40

20

oflloom Upwelting

54

Stratification

"

20

Winter

i....

Figure 2.- Mean (:!:sd) integrated chlorphyll-a (mg Chl-~ m-2) and primary production (mg C m-2

h-1) in sclectcd oceanographic seasons.

------ -- ---------

.. .

Figure 3.- Relative contribution (perccnt) of temporal (Period) and spatial (Area) factors to total

variancc in walcr-column integratcd chlorophyll-a (Chl-a) and production (Prod) data.