Copepod abundance in the western Irish Sea: relationship to physical regime, phytoplankton production and standing stock

The distinct patterns of stratification in the North Channeland stratified region of the western Irish Sea influence theseasonal abundance of phytoplankton. The 3–4 month productionseason in the stratified region was characterized by productionand biomass peaks in the spring (up to 2378 mg C m² day^–1and 178.4 mg chlorophyll m^–2) and autumn (up to 1280 mgC m^–2 day^–1 and 101.9 mg chlorophyll m^–2).Phytoplankton in the North Channel exhibited a short, late productionseason with a single summer (June/July) peak in production (4483mg Cm^–2 day^–1) and biomass (–160.6 mg chlorophyllm^–2). These differences have little influence on copepoddynamics. Both regions supported recurrent annual cycles ofcopepod abundance with similar seasonal maxima (182.8–241.810³ind. m^–2) and dominant species (Pseudocalanus elongatusand Acartia clausi). Specific rates of population increase inthe spring were 0.071 and 0.048 day¹ for the North Channel andstratified region, respectively. Increased copepod abundancein the stratified region coincided with the spring bloom, andwas significantly correlated with chlorophyll standing stock.Increased copepod abundance preceded the summer production peakin the North Channel. This increase was not correlated withchlorophyll standing crop, suggesting that a food resource otherthan phytoplankton may be responsible for the onset of copepodproduction prior to the spring bloom. Hetero-trophic microplanktonas an alternative food source, and advection of copepods fromthe stratified region, are proposed as possible explanationsfor copepod abundance increasing in advance of the summer peakin primary production.     

Life history, biomass and production of two planktonic cyclopoid copepods in a shallow subtropical reservoir

Two planktonic cyclopoid copepods (Tropocyclops prasinus andMesocyclops longisetus) were raised in the laboratory to obtainlife history information (duration of embryonic and post-embryonicdevelopment, reproductive performance, longevity, and stage-specificlength and weight values). Animals were maintained at 20 and25°C, and fed ad libitum. Development times were temperaturedependent when food was not limiting, with shorter periods ofembryonic and post-embryonic development and decreased longevityat 25°C. Laboratory data on the duration of developmentand biomass, together with population dynamics data obtainedin the field, were used to estimate summer and winter biomassand production of these species in a shallow reservoir, LagoaDourada, Brazil. The maximum production rate of T. prasinus,attained during summer, was 2.8 mg dry weight (DW) m^–3day^–1 and the highest daily production:biomass (P:B) ratiowas 0.29, whereas for M. longisetus the maximum production ratewas 1.4 mg DW m^–3 day^–1 and the highest daily P:Bratio was 0.39, in the winter. Over short time intervals (everyother day), there was great variability of the species productionrates. Species production rates were low compared to valuesreported in the literature for the same or other species ofequivalent sized copepods from both tropical and subtropicalregions.     

The seasonal abundance and production of Oithona nana (Copepoda:Cyclopoida) in Southampton Water

Recent studies indicate that Oithona spp. contribute significantlyto total copepod biomass. Little is known, however, about theirecological significance, particularly in the case of the estuarineOithona nana. A study comprising three sites within SouthamptonWater was conducted to evaluate the late-stage copepodite/adult(stages IV–VI) O. nana community, using 120-µm meshnets. Although present throughout the estuary, there was a strikingspatial gradient with O. nana most common in the upper estuary.A clear seasonal pattern was observed with O. nana as the mostabundant copepod species from late summer until early winter.It comprised 61% of all copepods recorded, with a biomass of757.22 mg C m^–3. Production estimates of O. nana werederived from the ‘instantaneous-growth’ approach,using appropriate growth equations. The estimated productionof O. nana ranged from 1.50 mg C m^–3 year^–1 withinthe lower estuary to 146.77 mg C m^–3 year^–1 in theupper estuary. In the upper estuary, this compares with productionrates of 187.47 mg C m^–3 year^–1 for all Acartiacongeners (excluding nauplii), the most common calanoid genus.Throughout the estuary, O. nana annual production represented18% of total copepod production clearly indicating that, atleast in the upper estuary, O. nana production may be directlycomparable with calanoid production.     

The productive and optical status of the oligotrophic waters of the Southern Aegean Sea (Cretan Sea), Eastern Mediterranean

Primary production, pigment concentrations and spectral measurementsof downwelling irradiance were made at four stations in fourseasons (spring, summer, autumn, winter) during 1994 in thewaters of the South Aegean Sea (Cretan Sea), Eastern Mediterranean.Rates of production were determined using in Situ incubationtechniques and included measurements at the surface microlayer.Depth-integrated values averaged over season were 5.66 mg Cm^–2 h^–1 for primary production and the correspondingchlorophyll (Ch1) a and phaeophytin (Phaeo) a values had meansof 4.87 and 1.21 mg m^–3 respectively. The assimilationratio remained very low (mean over season: 1.19 mg C mg^–2Chl a h^–1 as did the Phaeo a/Chl a ratio (mean over season:0.24). The annual production for the area was estimated to yield24.79 g C m^–2 year^–1. Primary production and Chla estimates showed statistically significant seasonal, spatialand depth variations. The spectral values of the attenuationcoefficient Kd (     

Production of Penilia avirostris in Kingston Harbour, Jamaica

The cladoceran Penilia avirostris is one of the more abundantand widespread members of the crustacean zooplankton in nearshoretropical and subtropical waters. Its abundance, biomass, fecundity,development rate and production were estimated in Kingston Harbour,Jamaica, during an 18 month period. Mean annual abundance ofPenilia was 1821 m^–3, while biomass (excluding eggs/embryos)was 2.87 mg ash-free dry-weight (AFDW) m^–3 (43.1 mg AFDWm^–2), accounting for 13% of the copepod community biomass.Fecundity increased with body size. There was no clear seasonalpattern of abundance, size or fecundity, nor were physical orbiological variables correlated to these variations. Developmenttime averaged 20.5 h for juveniles and 41.4 h for adult femalesduring incubations; there was no clear evidence of a diel patternto molting. Growth rate appeared to be exponential, with correspondingsomatic growth rates, averaging 0.27 day^–1 for juveniles,and 0.34 day^–1 for somatic plus reproductive growth inadult females. Annual production was estimated as 173 kJ m^–2year^–1,     

Production of Oikopleura longicauda (Tunicata: Appendicularia) in Toyama Bay, southern Japan Sea

Oikopleura longicauda occurred throughout the year in ToyamaBay, southern Japan Sea, and analysis of its size compositionand maturity revealed that reproduction was continuous overtheyear. Somatic growth production (P_g) varied with season from0.03 to 103 mg carbon (C) m^–2day^–1 (annual P_g 4.5g C m^–2), and house production (P_e) from 0.11 to 266 mgC m^–2 day^–1 (annualP_e 11.3 g C m^–2). The annualP_g/B ratio was 176. Compared with production data of some predominantzooplankton species in Toyama Bay, it is suggested that despitetheir smaller biomass, appendicularians are an important secondaryproducer.     

Production of tropical larvaceans in Kingston Harbour, Jamaica: are we ignoring an important secondary producer?

The larvacean community was observed during an 18 month periodat the mouth of eutrophic Kingston Harbour, Jamaica. Duringthis period, larvaceans averaged 3607 m^–3 with a biomassof 2.2mg ash-free dry weight m^–3 (32.6mg AFDW m^–2in a community dominated by Oiko pleura longicauda There wereno relationships between larvacean biornass and any size fractionof chlorophyll, suggesting that other factors must normallyregulate larvacean communities. The evidence indicates thatthis regulation is by predation. Annual production by larvaceanswas 586 kJ m^–3 year ^–1 (29.3 g AFDW m^–2 year^–1);production of houses could represent an added 300–600kJ m^–2 year. While copepod biomass was 10 times higherthan that of the larvaceans during the same period, copepodgrowth rates were only one.third those of larvaceans. Thus,larvacean annual production is at least 30% that of the copepods,due to their rapid growth rates, and at least 50% that of thecopepods when house production is considered. The contributionof larvaceans to plankton production has been underappreciatedhistorically when only their biomass is considered. ¹Present address :Monterey Bay Aquarium Research Institute 7700Sandholdt Road, Moss Landing, CA 95039-0628, USA     

Planktonic primary production in the German Wadden Sea

By combining weekly data of irradiance, attenuation and chlorophylla concentrations with photosynthesis (P) versus light intensity(E) curve characteristics, the annual cycle of planktonic primaryproduction in the estuarine part of the Northfrisian WaddenSea was computed for a 2 year period. Daily water column particulategross production ranged from 5 to 2200 mg C m^–2 day^–1and showed a seasonal pattern similar to chlorophyll a. Budgetcalculation yielded annual gross particulate primary productionsof 124 and 176 g C m^–2 year^–1 in 1995 and 1996,respectively. Annual amounts of phytoplankton respiration, calculatedaccording to a two-compartment model of Langdon [in Li,W.K.W.and Maestrini,S.Y. (eds), Measurement of Primary Productionfrom the Molecular to the Global Scale. International Councilfor the Exploration of the Sea, Copenhagen, 1993, pp. 20–36],and dissolved production in 1996, were both in the range of24–39 g C m^–2 year^–1. Annual total net productionwas thus very similar to particulate gross production (127 and177 g C m^–2 year^–1 in 1995 and 1996, respectively).Phytoplankton growth was low or even negative in winter. Inspring and summer, production/biomass (Pr/B) ratios varied from0.2 up to 1.7. Phytoplankton growth during the growth seasonalways surpassed average flushing time in the area, thus underliningthe potential of local phytoplankton bloom development in thispart of the Wadden Sea. The chlorophyll-specific maximum photosyntheticrate (P^B_max) ranged from 0.8 to 9.9 mg C mg^–1 Chl h^–1and was strongly correlated with water temperature (r² = 0.67).By contrast, there was no clear seasonal cycle in ^B, which rangedfrom 0.007 to 0.039 mg C mg^–1 Chl h^–1 (µmolphotons m^–2 s^–1)^–1. Its variability was muchless than P^B_max and independent of temperature. The magnitudeand part of the variability of P^B_max and ^B are presumably causedby changes in species composition, as evidenced from the rangeof these parameters found among 10 predominant diatom speciesisolated from the Wadden Sea. The ratio of average light conditionsin the water column (E_av) to the light saturation parameterE_k indicates that primary production in the Wadden Sea regionunder study is predominantly controlled by light limitationand that nutrient limitation was likely to occur for a few hoursper day only during 5 (dissolved inorganic nitrogen) to 10 (PO₄,Si) weeks in the 2 year period investigated.     

Population biomass, feeding, respiration and growth rates, and carbon budget of the scyphomedusa Aurelia aurita in the Inland Sea of Japan

We investigated the seasonal occurrence, wet : dry : carbon: nitrogen weight ratios, population biomass, gastric pouchcontents, and rates of feeding, growth and respiration of thescyphomedusa Aurelia aurita in the central part of the InlandSea of Japan. Aurelia aurita medusae began to appear in January/Februaryas ephyrae, reached annual maximum body size in July/August,and disappeared, presumably due to death, by November. Initialslow growth in early spring was followed by a period of exponentialgrowth (mean growth rate: 0.069 d^–1) between April andJuly. In the Ondo Strait, which is characterized by strong tidalmixing, the A. aurita population (mean carbon biomass: 66.0mg C m^–3) overwhelmingly dominated the zooplankton-communitybiomass (mean biomass of micro- and mesozooplankton: 23.7 mgC m^–3) between May and early August The gastric contentanalysis revealed that A. aurita ate almost all micro- and mesozooplankters,of which small copepods were most important. On the basis ofdigestion time for small copepods (60 min) and their abundancein the gastric pouch of field-collected A. aurita, we determinedthe weight specific feeding rates and clearance rates. The formerincreases linearly with increasing copepod abundance, but thelatter was relatively constant irrespective of the food supply.We also measured the respiration rates of A. aurita and expressedthem as functions of body weight and temperature. These physio-ecologicalparameters enabled us to construct the carbon budget of theA. aurita population typical of early summer in the Ondo Strait.Predicted population-feeding rate (6.07 mg C m^–3 d^–1)was higher than the population-food requirement for both metabolismand growth (4.55 mg C m^–3 d^–1), indicating thatfood supply was sufficient to sustain the observed growth rate.This feeding rate was equivalent to 26% of micro- and mesozooplanktonbiomass, a significant impact on zooplankton.     

Size-fractionated primary production studies in the vicinity of the Subtropical Front and an adjacent warm-core eddy south of Africa in austral winter

Results are presented of size-fractionated primary productionstudies conducted in the vicinity of the Subtropical Front (STF),an adjacent warm-core eddy, and in Sub-antarctic waters duringthe third South African Antarctic Marine Ecosystem Study (SAAMESIII) in austral winter (June/July) 1993. Throughout the investigation,total chlorophyll (Chl a) biomass and production were dominatedby small nano- and picophytoplankton. No distinct patterns intotal Chl a were evident. At stations (n = 7) occupied in thevicinity of the STF, total integrated biomass values rangedfrom 31 to 53 mg Chl a m^–2. In the vicinity of the eddy,integrated biomass at the eddy edge (n = 3) ranged from 24 to54 mg Chl a m^–2 and from 32 to 43 mg Chl a m^–2 inthe eddy (n = 2). At the station occupied in the Sub-antarcticwaters, total integrated biomass was 43 mg Chl a m^–2.Total daily integrated production was highest at stations occupiedin the vicinity of the STF and at the eddy edge. Here, totalintegrated production ranged from 150 to 423 mg C m^–2day^–1 and from 244 to 326mg C m^–2 day^–1, respectively.In the eddy centre, total integrated production varied between134 and 156 mg C m^–2 day^–1. At the station occupiedin the Sub-antarctic waters, the lowest integrated production(141 mg C m^–2 day^–1) during the entire survey wasrecorded. Availability of macronutrients did not appear to limittotal production. However, the low silicate concentrations duringthe survey may account for the predominance of small nano- andpicophytoplankton. Differences in production rates between theeddy edge and eddy core were related to water column stability.In contrast, at stations occupied in the vicinity of the STF,the control of phytoplankton production appears to be relatedto several processes, including water column stability and,possibly, iron availability.     

Daily changes in population structure and production of Eudiapomus gracilis (G.O. Sars) (Copepoda, Calanoida) during summer in a shallow lake (Balaton, Hungary)

Population structure and production of Eudiaptomus gracilis(G.O. Sars) have been calculated from daily measurements inLake Balaton for one month during each summer in 1975 and 1977.Fecundity was different in the two years 6.98 ? 1.16 and 10.68? 1.42 in 1975 and 1977, respectively. A total of 80% and 64%of the population were made up of larvae in 1975 and 1977, respectively.The ratio of males to females was 1:1.63 and 1:1.1, respectively.In 1975 it was possible to follow the development of cohorts,19 –20 days in the former year, 17 –20 days in thelatter. In both years of examination 80 – 83% of naupliiand 12–15% of copepodites were eliminated. Daily net biomassproduction was 6.88 mg (dry wt.)/m³ in 1975 and 1.94 mg (drywt.)/m³ in 1977. Ratios of eggs, nauplii and copepodites indaily production was 1:2.4:1.4 in 1975 and 1:1.0:1.0 in 1977.The daily potential biomass production were 34.40 mg (dry wt.)/m³ and 10.28 mg (dry wt.)/m³ and the elimination were 80 and81 wt.%, respectively. P/B ratio — allowing for net productionvalues — was nearly the same in both periods of investigation(0.12 and 0.099 respectively).     

Structure and Function of an Age Series of Eucalypt Plantations in Central Himalaya. I. Dry Matter Dynamics

The biomass and net primary productivity (NPP) of 2- to 8-year-oldplantations of Eucalyptus tereticornis Sm. (= E. hybrid) growingin the tarai (a level area of superabundant water) region ofCentral Himalaya were estimated. Allometric equations for allthe above-ground and below-ground components of trees and shrubswere developed for each stand. Understorey, forest floor biomassand litter fall were also estimated from stands. Shrubs appearedfirst at 5-year-old plantation. The biomass of vegetation, forestfloor littermass, tree litter fall and net primary productivity(NPP) of trees and shrubs increased with the increase in plantationage, whereas herb biomass and NPP significantly (P < 0·01)decreased with the increase in plantation age. The total plantationbiomass increased from 7·7 t ha^–1 in the 2-year-oldto 126·7 t ha^–1 in the 8-year-old plantation andNPP from 8·6 t ha^–1 year^–1 in the 2-year-oldto 23·4 t ha^–1 year^–1 in the 8-year-old plantation.The biomass accumulation ratio ranged from 0·81 to 5·93. Eucalyptus tereticornis Sm, plantation, biomass, forest floor, litter fall, net primary productivity, biomass accumulation ratio     

Biomass and production of the major dominant crustacean zooplankton in a tropical Rift Valley lake, Awasa, Ethiopia

Seasonal variation of the biomass (B), production (P) and P/Bratio of the numerically dominant crustaceans in Lake Awasa(Mesocydops aequatonalis stmilts, Thermocyclops consunilis andDiaphanosoma exisum) were studied during 1986 and 1987. Quantitativenet samples (64 (xm mesh) were taken at three stations on 10day intervals throughout 1986, and the dry weights and developmenttimes for each life stage were obtained from laboratory measurementsand cultures Total biomass of most of the dominant crustaceans,determined from 390 samples during 1986, was 44.85 mg m^–3(dry weight, DW) with adult females of Mesocyclops making >43.5%.Alona diaphana, another common crustacean, is dealt with ina separate paper, as are the Rotifera. Production of the dominantcrustaceans during 1986 was estimated by the growth incrementsummation (Winberg) and instantaneous growth (Ricker) methodsThe annual integrated production of the two dominant cyclopoidsis 535.2 mg (DW) m^–3 (Winberg) while annual crustaceanproduction totals 2.5 g (DW) m^–3 (Ricker) The mean annualP/B ratio for individual species and stages varied from 221.0for Diaphanosoma, to 121.7-143.0 for nauplii and 9.8–187 for copepodites of the cyclopoids It was 55 8 for the dominantzooplankton species Low or high zooplankton production and biomassturnover rates (P/B) cannot be used to characterize all tropicallakes consistently However, production per unit biomass is likelyto be higher in tropical lakes.     

Carbon flux by seasonal vertical migrant copepods is a small number

The abundant species of Calanus that dominate the mesozooplanktonof high North Atlantic latitudes overwinter at depths >500m, when the population loses 70–80% of its biomass bypredation and physiological stress. This represents an annualflux of carbon, obtained in the photic zone, into the interiorof the ocean of 274.5 mg C m^–2 year^–1, or 0.0018Gt C year^–1 for the North Atlantic. This is a small valuecompared with the flux of respiratory carbon by diel migrantsin warmer oceans and, when extrapolated to a global flux (0.012–0.018Gt C year^–1 over areas where winter migrations are importantis also small compared with computations of the global sinkingflux of particles through 200 m (1.6–3.8 Gt C year^–1or other relevant global carbon fluxes in the oceans.     

Seasonal and interannual variability of chlorophyll a and primary production in the Equatorial Atlantic: in situ and remote sensing observations

The seasonal variability of phytoplankton in the EquatorialAtlantic was analysed using Sea-viewing Wide Field-of-view Sensor(SeaWiFS)-derived chlorophyll a (Chl a) concentration data from1998 to 2001, together with in situ Chl a and primary productiondata obtained during seven cruises carried out between 1995and 2000. Monthly averaged SeaWiFS Chl a distributions werein agreement with previous observations in the Equatorial Atlantic,showing marked differences between 10° W in the EasternTropical Atlantic (ETRA) and 25° W in the Western TropicalAtlantic (WTRA) provinces (Longhurst et al. 1995. J. PlanktonRes., 17, 1245–1271). The seasonal cycle of SeaWiFS-derivedChl a concentration calculated for 0–10° S, 0–20°W (ETRA) is consistent with in situ Chl a measurements, withvalues ranging from 0.16 mg m^–3, from February to April,to 0.52 mg m^–3 in August. Lower variability was observedin 10° N–10° S, 20–30° W (WTRA) whereminimum and maximum concentrations occurred in April (0.15 mgm^–3) and in August (0.24 mg m^–3), respectively.A significant empirical relationship between depth-integratedprimary production and in situ measured sea surface Chl a wasfound for ETRA, allowing us to estimate the seasonal cycle ofdepth-integrated primary production from SeaWiFS-derived Chla. As for Chl a, this model was verified in a small area ofthe Eastern Equatorial Atlantic (0–10° S, 0–20°W), although in this instance it was not completely able todescribe the magnitude and temporal variability of in situ primaryproduction measurements. The annual euphotic depth-integratedprimary production rate estimated for ETRA by our empiricalmodel was 1.4 Gt C year^–1, which represents 16% of theopen ocean primary production estimated for the whole AtlanticOcean.     

Metazooplankton dynamics and secondary production of Daphnia magna (Crustacea) in an aerated waste stabilization pond

The seasonal dynamics of metazooplankton biomass was monitoredin an aerated waste stabilization pond during three consecutiveyears (1994–1996). The pond showed a low diversity ofplanktonic metazoans because of elevated pH, relatively highconcentration of free dissolved ammonia and low oxygen concentration.The planktonic community was composed of the anomopod branchiopodDaphnia magna, and the cyclopoid copepods Cyclops vicinus andCyclops strenuus. Both predation by cyclopoids and competitionwith D.magna excluded rotifers from the pond, except duringa short period in spring 1996. Daphnia magna was the dominantorganism from a biomass point of view. In parallel with biomass,demographic parameters, secondary production and the spatialdistribution of D.magna were studied. A significant seasonaland interannual variation in the density, biomass and productionof D.magna was observed. The maximum density of daphnids variedfrom 264 x 10³ to 686 x 10³ individuals m^–2 and the maximumbiomass from 4 to 30 g dry weight (DW) m^–2. The annualnet production was high compared with the production of Daphniain natural environments, ranging from 288 to 593 g DW m^–2year^–1. The annual net production of exuviae accountedfor ~25% of the total annual net production. Harvesting of daphnidsfor commercial applications that took place during the productiveperiod did not have any discernible effect on the populationdynamics of D.magna. Sexual reproduction was not observed duringthe three studied years. Negative mortality rates, occurringduring early spring, however, indicated that recruitment fromephippia was effective in the pond of Differdange and that sexualreproduction took place before 1994. Swarming was regularlyobserved in relation to high densities.     

The seasonal population changes and carbon budget of the calanoid copepod Boeckella minuta Sars in a newly formed sub-tropical reservoir

The population carbon budget and seasonality of Boeckella minutain a newly formed subtropical reservoir were examined 3 yearsafter the reservoir filled. Average daily biomass was 26.4 mgC m^–3 and the annual population carbon budget was: consumption2470, egestion 1482, assimilation 988, production 493 and respiration495, mg C m^–3 year^–1, and the average P/B and P/Aratios were 0.08 and 0.5 respectively. Clutch size and reproductiveeffort (egg production/assimilation) were low, and the proportionof males decreased throughout the population cycle. The seasonalabundance pattern changed from perennial (pre-filling years)to a 7 month cycle. It is suggested that eutrophication andthe spring bloom of cyanobacteria may have accentuated a seasonaldecrease in reproductive effort and survival, leading to anabsence of planktonic stages during summer, and that restingeggs facilitated population survival during the summer periodof stratification.     

Biomass, Productivity and Energetics in Himalayan Alder Plantations

Biomass, net primary production and energy fixation in an agesequence of Himalayan alder (Alnus nepalensis D. Don) plantationswere estimated in the Kalimpong forest division of the easternHimalayas. Biomass in the plantations ranged from 106 t ha^–1(7-year stand) to 606 t ha^–1 (56-year stand) demonstratingthe potential of the alder for accumulating large biomass. Netprimary production and net energy fixation rates of the plantationswere reduced by nearly half in the 7-year stand (25 t ha^–1year^–1; 421 x 10⁶ kJ ha^–1 year^–1) comparedwith the 56-year stand (13 t ha^–1 year^–1; 215 x10⁶ kJ ha^–1 year^–1). Compartmental models of energystorage and flow rates were developed for the 7-year and 56-yearstands. The production efficiency, energy conversion efficiencyand energy efficiency in N₂ fixation have inverse relationshipswith plantation age. These efficiencies, when treated with eachother, showed significant exponential functions. Alnus nepalensis D. Don, Himalayan alder, plantation age, biomass, net primary production, energy flow, efficiencies     

Density and distribution of bacterioplankton and planktonic ciliates in the Bering Sea and North Pacific

The total number of planktonic bacteria in the upper mixed layerof the Bering Sea during the late spring-early summer periodranged between 1 and {small tilde}4 x 10⁶ ml^–1 (biomass10–40mg C m^–3). In the northern Pacific, along 47–52⁶N,the corresponding characteristics of the bacterioplankton densityin the upper mixed water layer were: total number 1–2x 10⁶ cells ml^–1 and biomass 15–46mg C m^–3Below the thermocline at 50–100 m, the density of bacterioplanktonrapidly decreased. At 300 m depth, it stabilized at 0.1–0.2x 106 cells ml^–1. The integrated biomass of bacterioplanktonin the open Bering Sea ranged between 1.2 and 3.6 g C m^–2(wet biomass 6–18 g m^–2) Its production per dayvaried from 2 to 23 mg C m^–3 days^–1 in the upper0–100 m. The numerical abundance of planktonic ciliatesin this layer was estimated to be from 3 to l0 x 10³ cells l^–1,and in the northern Pacific from 0.4 to 4.5 x 10³ l^–2.Their populations were dominated by naked forms of Strombidium,Strombilidium and Tontonia. In some shelf areas, up to 40% ofthe total ciliate population was represented by the symbioticciliate Mesodinium rubrum. The data on the integrated biomassof basic groups of planktonic microheterotrophs are also presented,and their importance in the trophic relationships in pelagiccommunities of subarctic seas is discussed.     

Simulated annual plankton production in the northeastern Pacific Coastal Upwelling Domain

A microcomputer simulation model is presented that describesthe generalized plankton production dynamics, in the surfacemixed layer, of the Juan de Fuca Eddy located on the southwesternBritish Columbia continental shelf. The Juan de Fuca Eddy simulationmodel evaluates how the annual biomass production of diatoms,copepods and euphausiids is forced by plankton feeding interactions,seasonal variability in upwelling, water temperature and solarradiation, and generalized fish predation. The model estimatesannual primary production of 345 g C m^–2 year^–1and secondary production of 19.4 g C m^–2 year^–1for copepods and 6 g C m^–2 year^–1 for euphausiids,during 1985–89; -90% of the annual plankton productionwas generated during the April-October upwelling season. Perturbationsof 22 abiotic and biotic parameters, one at a time by ±10%of nominal values, indicated that oceanic variability (e.g.upwelling rate) most strongly affected primary production. Conversely,zooplankton production was most sensitive to variability inbiological parameters describing zooplankton grazing potentialand growth (e.g. gross growth efficiency). Simulated seasonalbiomass patterns of diatoms, copepods and euphausiids were foundto closely match empirical data. However, euphausiid biomassproduction in the Juan de Fuca Eddy alone was unable to meetthe demands of estimated pelagic fish consumption. Local Eddyeuphausiid populations had to be supplemented, from regionaleuphausiids. by a mechanism that is proposed to be linked tothe seasonal pattern and intensity of positive Ekman transport(upwelling).