Population dynamics of the scyphomedusa Aurelia aurita in Southampton Water

The population dynamics of the scyphomedusa Aurelia aurita inSouthampton Water is characterized. Strobilation, indicatedby the presence of 1 mm ephyrae, occurred from the end of Januaryto the middle of March. Maximum abundances of up to 8.71 m^–3occurred soon after ephyrae release, after which numbers declinedsteadily until the end of June, when the population was absentfrom Southampton Water. The residence time of 3–4 monthsis somewhat less than that reported in many other areas, includingKiel Bight and Gullmarfjord. The carbon biomass of A.auritaaccounted for 92–97% of the predominant gelatinous biomass(A.aurita, Pleurobrachia pileus and Phialidium hemisphericum)in the upper estuary, and this reached a maximum of 30.2 mgC m^–3 in May 1990 and 27.6 mg C m^–3 in June 1991.Coincident with increased water temperature and mesozooplanktonabundance during May, growth rates increased from 0.02–0.30mm day^–1 to a peak of 4.8 mm day^–1, with a maximumbell diameter of 120–140 mm reached in late May/earlyJune. Size to maturity was variable, although the smallest medusaobserved to be ‘ripe’, i.e. containing dividingeggs and planula larvae in the brood sacs on the oral arms,were 64–71 mm. Aurelia aurita is believed to be endemicto Southampton Water, but because of the double high water inthe area, short flushing rates of between 4.5 and 20 days maybe responsible for such short residence times of Aurelia medusae.The effects of strong NE winds were considered as factors governingthe distribution of medusae in years of atypical temporal abundance.     

Interannual changes in the biomass of the Black Sea gelatinous zooplankton

The 15 year changes in the total gelatinous biomass consistof a general trend to increase, from 250 gm^–2 in 1980to 2500 g m^–2 in 1995, and fluctuations with a periodof –4 years performed against the background of this trendin the upper 150 m layer. Different species occupying distincttrophic niches form these peaks. When represented as the percentageof the total zooplankton biomass, Aurelia aurita and Mnemiopsisleidyi exhibit the contra-phase fluctuations where a sharp increasein M.leidyi is accompanied by a decrease in the A.aurita biornass.     

Population dynamics of Aurelia aurita (Scyphozoa) from an isolated brackish lake, with particular reference to sexual reproduction

The annual cycle of abundance, growth and sexual reproductionof the scyphomedusa Aurelia aurita was examined over a 12 monthperiod in an isolated, shallow, brackish, man-made body of water:Horsea Lake, England. Strobilation started in December and ephyraewere present through June in varying numbers, suggesting a 7month period of near-continuous recruitment. Horsea Lake hasa dense A.aurita population, with the peak abundance of 24.9m^–3 occurring in mid-May. Medusae (>10 mm) were presentin the water column from March through January. Maximum belldiameter of 105 mm was observed in late September. However,medusa growth was very poor (G ranged between –0.03 and0.07 day^–1 over a 12 month period), and monthly mean belldiameters were typically <50 mm. For most of the year, theabundant A.aurita population was most likely severely food limitedas a result of a numerically and species-poor mesozooplanktoncommunity dominated by the calanoid copepods Acartia margalefiand Acartia tonsa. Nevertheless, the very small A.aurita medusaewere still able to attain sexual maturity and reproduce. Ripefemale medusae carrying fertilized eggs and planula larvae werefirst observed in May and June, although the main period ofplanula larva production was September-December. In November,all females were ripe, the smallest being 19–20 mm belldiameter. At both Horsea Lake and a nearby productive estuary,Southampton Water, planula larva production increased linearlywith wet weight, although compared with the larger A.auritamedusae from Southampton Water, reproductive output at HorseaLake was low. Aurelia aurita in Horsea Lake showed plasticityin its population characteristics in response to environmentalconditions, with both fecundity and size to maturity varyingon a seasonal basis. Medusae appeared to partition the availablefood resources into either somatic growth when food was abundantor reproductive effort when food was scarce.     

Biomass and size structure of the scyphomedusa Aurelia aurita in the northwestern Black Sea during spring and summer

The abundance, biomass and size structure of the scyphomedusa,Aurelia aurita, was measured during two research cruises tothe northwestern Black Sea (July–August 1995 and April–May1997). Average biomass of Aurelia was relatively constant (132–179g wwt m^–2) throughout the investigation period and similarto previous years. Abundance and biomass at individual stationsappeared to be unrelated to temperature and salinity when thelatter exceeded ~13. Biomass was low at coastal stations inthe plume of the Danube where depth was <20 m and salinitydropped to <11. The spring cruise (April–May) coincidedwith, or just followed the peak of strobilation. The summercruise (July–August) took place near the beginning ofplanulae larvae release. The population size structure was dominatedby small individuals in spring, while large medusae prevailedmainly in late summer. Aurelia was, on average, larger at deepwater stations during summer, suggesting that per capita foodsupply was higher further offshore. The individual body massincreased from spring through summer. Accordingly, the volume(wet wt) to length (bell diameter) relation changed significantly.If all medusae measured throughout the seasons were pooled,volume (V, in cm³) was related to length (L, in cm) accordingto V = 0.08 L^2.71, which is similar to measurements conductedin other coastal areas. In contrast to the common conjecture,we did not find inverse relations between biomasses of Aureliaand the combjelly Mnemiopsis leidyi. Preliminary feeding experimentsindicate that Aurelia may feed upon small Mnemiopsis. The significanceof indirect trophic relations and direct feeding interactionsamong the gelatinous zooplankton in the Black Sea has importantconsequences for the energy flow along the food web and, therefore,needs further study.     

Plant Growth in Relation to the Supply and Uptake of NO3-: A Comparison Between Relative Addition Rate and External Concentration as Driving Variables

Two approaches to quantifying relationships between nutrientsupply and plant growth were compared with respect to growth,partitioning, uptake and assimilation of NO₃^– by non-nodulatedpea (Pisum sativum L. cv. Marma). Plants grown in flowing solutionculture were supplied with NO₃^– at relative addition rates(RAR) of 0·03, 0·06, 0·12, and 0·18d^–1, or constant external concentrations ([NO₃^–)of 3, 10, 20, and 100 mmol m^–3 over 19 d. Following acclimation,relative growth rates (RGR)approached the corresponding RARbetween 0·03–0.12 d^-1, although growth was notlimited by N supply at RAR =0.18 d^-1. Growth rates showed littlechange with [NO₃–] between 10–100 mmol m^–3(RGR=0·15 –0·16 d^-1). The absence of growthlimitation over this range was suggested by high unit absorptionrates of NO₃^–, accumulation of NO₃^– in tissues andprogressive increases in shoot: root ratio. Rates of net uptakeof NO₃^– from 1 mol m^–3 solutions were assessed relativeto the growth-related requirement for NO₃^–, showing thatthe relative uptake capacity increased with RGR between 0·03–0·06d^–1 , but decreased thereafter to a theoretical minimumvalue at RGR     

Growth and ingestion rates of larval fish populations in the coastal waters of Israel

Clupeoid larvae were collected on eight cruises between February1984 and February 1985 in the coastal waters of Israel. Fromanalysis of daily growth increments of otoliths, growth ratesof the abundant clupeoids, Engraulis encrasicolus, Sardina pilchardusand Sardinella aurita were found to be 0.55 mm day^–1,0.67 mm day^–1 and 0.60 mm day^–1, respectively, duringthe first month after hatching. Ingestion rates were estimatedusing an equation from the literature relating ingestion andgrowth of larval fish. Ingestion calculated for populationsof fish larvae in pelagic waters ranged from 0 to >23 mgC m^–2 day^–1 with maximum rates observed in April.Annual ingestion by larval fish at a pelagic station near Haifawas calculated to be 2.2 g C m^–2 year^–1, 10–20%of annual primary production estimated from ¹⁴C uptake.     

Nitrogen Utilization in N-limited Barley During Vegetative and Generative Growth: III. POST-ANTHESIS KINETICS OF NET NITRATE UPTAKE AND THE ROLE OF THE RELATIVE ROOT SIZE IN DETERMINING THE CAPACITY FOR NITRATE ACQUISITION

Barley (Hordeum vulgare L., cvs Golf, Mette, and Laevigatum)was grown under nitrogen limitation in solution culture untilnear maturity. Three different nitrogen addition regimes wereused: in the ‘HN’ culture the relative rate of nitrate-Naddition (RA) was 0·08 d^–1 until day 48 and thendecreased stepwise to, finally, 0·005 d^–1 duringgrain-filling; the ‘LN’ culture received 45% ofthe nitrogen added in HN; the ‘CN’ culture was maintainedat RA 0·0375 d^–1 throughout. Kinetics of net nitrateuptake were measured during ontogeny at 30 to 150 mmol m^–3external nitrate. V_max (which is argued to reflect the maximuminflux rate in these plants) declined with age in both HN andLN cultures. A pronounced transient drop was observed just beforeanthesis, which correlated in time with a peak in root nitrateconcentration. Similar, but less pronounced, trends were observedin CN. The relative V_max (unit nitrogen taken up per unit nitrogenin plants and day) in all three cultures declined from 1·3–2·3d^–1 during vegetative growth to 0·1–0·7d^–1 during generative growth. These values are in HN andLN cultures 15- to more than 100-fold in excess of the demandset by growth rates throughout ontogeny. Predicted balancingnitrate concentrations (defined as the nitrate concentrationrequired to support the observed rate of growth) were below6·0 mmol m^–3 in HN and LN cultures before anthesisand then decreased during ontogeny. In CN cultures the balancingnitrate concentration increased during grain-filling. Apartfrom the transient decline during anthesis, most of the effectof ageing on relative V_max can be explained in terms of reducedcontribution of roots to total biomass (R:T). The loss in uptakeper unit root weight is largely compensated for by the declinewith time in average tissue nitrogen concentrations. The quantitativerelationships between relative V_max and R:T in ageing plantsare similar to those observed for vegetative plants culturedat different RAs. The data support the contention that the capacity for nitrateacquisition in N-limited plants is under general growth control,rather than controlled by specific regulation of the biochemicalpathway of nitrate assimilation. Key words: Barley, nitrogen concentration, root: total plant biomass ratio, V_max     

Biomass, feeding and production of Noctiluca scintillans in the Seto Inland Sea, Japan

The abundance and biomass of the large heterotrophic dinoflagellateNoctiluca scintillans, together with the changes in its potentialprey items, were monitored in the Seto Inland Sea, Japan, duringsummer 1997 (17 July-11 August). Growth and grazing rates ofNscintillans fed natural plankton populations were also measuredeight and seven times, respectively, during the survey period.The abundance and biomass of N scintillans averaged over thewater column (19 m) were in the range 1–345 cells 1^–1(temporalaverage = 93 cell1^–1) and 0.1–49.6 µg C l^–1(temporalaverage = 13.8 µg C l^–1; three times higher thanthat of calanoid copepods during the same period). Noctilucascintillans populations followed the changes in phytoplankton:N.scintillans biomass was increasing during the period of diatomblooms and was at a plateau or decreasing during periods oflow chlorophyll a. The growth rates of N.scintillans (µ)were also consistent with the wax and wane of the N.scintillanspopulation: N.scintillans showed highest growth rates duringdiatom blooms. A simple relationship between µ and chlorophylla concentration was established, and the production of N.scintillanswas estimated using this relationship and the measured biomass.The estimated production averaged over the water column wasin the range >0.1–5.2 µg C l^–1 day^–1(temporalaverage = 1.4 µg C l^–1 day^–1; 64% of the productionof calanoid copepods during the same period). Diatom clearancerates by N.scintillans were in the range 0.10–0.35 mlcell^–1 day^–1, and the phytoplankton population clearanceby N.scintillans was >12% day^–1. Thus, although thefeeding pressure of N.scintillans on phytoplankton standingstock was low, N.scintillans was an important member of themesozooplank-ton in terms of biomass and production in the SetoInland Sea during summer.     

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,     

Aspects of the feeding ecology of turbid water zooplankton. In situ studies of community filtration rates in silt-laden Lake le Roux, Orange River, South Africa

Diel vertical studies of zooplankton community filtration rates(CFR) were undertaken in situ over two annual cycles in a shelteredbay of Lake le Roux, a large silt-laden oligotrophic reservoirin the arid subtropics of South Africa. The grazer communitywas dominated by a copepod, Meradiaptomus meridianus, whileDaphnia gibba. D. barbara and Moina brachiara accounted forthe balance. Spot estimates of CFR varied from 0.1 to 75% d^–1( = 12.2) in the upper 10 m, while depth-integrated values ranged seasonally from 0.1 to 15% d^–1 ( = 7.4). Most variation in CFR was attributable toseasonal changes in grazer biomass (0–408, = 58.2 µg 1^–1 or 3–1000, 360 mg m^–2 dry wt), and temperature (12–22C). Thesevariables are used to construct multiple linear regression modelsfor the prediction of CFR in this system. Some higher CFR values(up to 260% d^–1 were measured in wanner (up to 26.5C)surface waters with an unusually rich zooplankion (786 rg 1^–1).No significant did vertical changes in CFR or grazer biomasswere observed. Both variables declined sharply with depth. Inorganicturbidity dominated the seston, and algal carbon probably accountedon average for less than about 20% of the total POC available.The feeding responses of this turbid-water community were generallyconsistent with observations made on other assemblages, apartfrom seemingly high specific filtration rates which, atypically,were inversely related to temperature.     

Photoadaptation in Antarctic phytopfankton: variations in growth rate, chemical composition and P versus I curves

The response of phytoplankton to variations in the light regimewas studied during the VULCAN and ACDA cruises in the Antarctic.Unenriched batch cultures of 12–19 days' duration reachedchl concentrations of 10–50 µg^–1 and exhibitedexponential growth rates, with the maximal rate being 0.41 doubl,day^–1. Ice edge algae exhibited maximum growth rates atphoton flux densities (PFD) of 30–100 µE m^–2S^–1and the growth rate was reduced by about 30% at 500–1000µE m^–2S^–1 The chl/C ratio ranged between 0.004and 0.018, with the lowest ratios at PFDs above 500 µEm^–2S^–1 chl/C ratios were also below maximum at PFDsbelow 40–50 µE m^–2S^–1 The C:N:P ratioswere close to the Redfield ratios; the Si/C ratio averaged 0.16(atoms), and the ATP/C ratio averaged from 0.0024 to 0.0050in different culture senes. When thawed after having been frozenfor 10 days, shade-adapted cultures were in a much better conditionthan sun-adapted ones. P versus I data showed that the maximumassimilation number varied from 0.75 to 4.4 µg C (µgchl)^–1h^–1. It varied inversely with the chl/C ratio;therefore the maximum carbon turnover rate varied little betweensamples (0.024/0.035 h^–1). Low biomass communities exhibitedrelatively high values for (the initial slope of P versus Icurves), low values for 1_sat (160–330 µE m^–2S^–1),and they were susceptible to photoinhibition. In contrast, communitiesdominated by Odontella weissflogii exhibited low values for, a high value for I_sat (560 µE m^–2S^–1 andthey tolerated high PFDs. The photo-adaptational status of thephytoplankton in natural water samples is discussed relativeto the profile of water column stability and mixing processes.     

Effect of u.v.-B irradiance on the response of 15N-nitrate uptake of Lauderia annulate and Synedra planctonica

The marine diatoms Lauderia annulata and Synedra planctonicaharvested during exponential growth were exposed to differentdoses of u.v.-B (286, 439 and 710 J m^–2 d^–1) for2 days. Uptake of ¹⁵N-nitrate was estimated before, during andafter u.v.-B radiation over 2 days. Exposure to high levelsof u.v.-B (710 J m^–2 d^–1) caused irreversible damageat the second daily irradiance. Lauderia cells were less affectedby u.v.-B stress than Synedra cells. ¹⁵N-nitrate uptake wasreduced under u.v.-B irradiance but could be reactivated within1 day following exposure to a low dose (286 J m^–2 d^–1).Higher levels of u.v.-B radiation (710 J m^–2 d^–1)led to irreversible damage. The pattern of ¹⁵N-incorporationinto several amino acids of Lauderia varied after 2 days ofu.v.-B radiation. ¹⁵N enrichment of glutamine increased markedlyafter u.v.-B stress (717 J m^–2 d^–1) whereas ^I5Nexcess of aspartic acid was significantly reduced. Results arediscussed with reference to the u.v.-B damage of the nitratetransport system.     

Feeding and growth rates of the doliolid, Dolioletta gegenbauri Uljanin (Tunicata, Thaliacea)

The goal of this research is to enhance our knowledge of thecontributions of doliolids to the planktonic community as consumersand secondary producers. The objectives are to quantify feedingand growth rates of Dolioletta gegenbauri gonozooids at fourfood concentrations and four temperatures in order to determinetheir impact as grazers throughout the water column. Althoughdoliolids are abundant in numerous regions of the coastal ocean,and are considered to be major planktonic grazers, data on ratesof feeding and growth are scarce. Laboratory experiments wereconducted at 16.5, 20, 23.5 and 26.5°C to quantify removalof a 50:50 volumetric concentration of Thalassiosira weissflogiiand Rhodomonas sp. at four different food concentrations of20, 60, 160 and 390 µg C l^–1. Results from theseexperiments suggest that clearance rates are similar at concentrationsfrom 20 to 60 µg C l ^–1, and decrease as the foodconcentrations increase to 160 and 390 µg C l ^–1.The ingestion rates increase over a range of phytoplankton concentrationsfrom 20 to 160 µg C l ^–1, then decrease when abnormallyhigh concentrations of 390 µg C l ^–1 are offered.Clearance and ingestion rates increase as temperature increasesfrom 16.5 to 26.5°C. The exponential growth rates rangefrom k = 0.2–0.7, with the lowest rates occurring at thehighest food concentration. Growth rates increase with increasingtemperature from K = 0.1–0.3 at 16.5°C to 0.45–0.7at 26.5°C. In each case, the small- and medium-sized zooidshad higher growth rates than the larger gonozooids. These resultssuggest that doliolid feeding and growth rates are a functionof environmental food concentrations and temperatures, and implythat they can be important consumers in a changing neritic environment.     

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.     

Phytoplankton and zooplankton development in a lowland, temperate river

The longitudinal and seasonal patterns of plankton developmentwere examined over 2 years in a lowland, temperate river: theRideau River (Ontario, Canada). Following an initial decreasein phytoplankton and zooplankton biomass as water flowed fromthe headwaters into the Rideau River proper, there was an increasein chlorophyll a (chl a) and zooplankton biomass with downstreamtravel. At approximately river km 60, both phytoplankton andzooplankton reached their maximum biomass of 27 µg l^–1(chl a) and 470 µg l^–1 (dry mass), respectively.Downstream of river km 60, the biomass of both planktonic communitiesdeclined significantly despite increasing nutrient concentrationsand favorable light conditions. These downstream declines maybe due to the feeding activity of the exotic zebra mussel (Dreissenapolymorpha) which was at high density in downstream reaches(>1000 individuals m^–2). There was no evidence forlongitudinal phasing of phytoplankton and zooplankton, as increasesand decreases in chl a and zooplankton biomass appeared to coincide.Overall, chl a was best predicted by total phosphorus (R²=0.43),whereas zooplankton biomass was best predicted by chl a (R²=0.20).There was no evidence for significant grazing effects of zooplanktonon phytoplankton biomass.     

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.     

Microzooplankton grazing in a coastal embayment off Concepcion, Chile, (~36{degrees} S) during non-upwelling conditions

The impact of grazing by natural assemblages of microzooplanktonwas estimated in an upwelling area (Concepción, Chile)during the non-upwelling season in 2003 and 2004. Seawater dilutionexperiments using chlorophyll a (Chl a) as a tracer were usedto estimate daily rates of phytoplankton growth and microzooplanktongrazing. Initial Chl a concentrations ranged from 0.4 to 1.4mg Chl a m^–3 and phytoplankton prey biomass and abundancewere numerically dominated by components <20 µm. Phytoplanktongrowth and microzooplankton grazing rates were 0.19–0.25day^–1 and 0.26–0.52 day ^–1, respectively.These results suggest that microzooplankton exert a significantremoval of primary production (>100%) during the non-upwellingperiod.     

Zooplankton growth rates: the larvaceans Appendicularia, Fritillaria and Oikopleura in tropical waters

The growth rates of Appendicularia sicula, Fritillaria borealissargassi, Fritillaria haplostoma, Oikopleura dioica and Oikopleuralongicauda were determined from microcosms incubated in situat 23C in Jamaican waters. Experiments were conducted fromoligotrophic offshore waters, through mesotrophic Lime Cay andeutrophic Kingston Harbour in both natural and nutrient-enhancedphytoplankton communities. Length-weight relationships werecalculated for two of these species: O.longicauda log W=2.47log TL –6.10 and F.haplostoma log W=2.44 log TL –7.37,where weight (W) is in micrograms and trunk length (TL) is inmicrometres. Instantaneous growth rates averaged 1.7–2.5day^–1 for the five species and were observed as high as3.3 day^–1 These instantaneous rates are equivalent todaily specific growth rates averaging 4.6–11.4 and rangingup to 28. In larger genera, growth rates were related positivelyto picoplankton and nanoplankton concentration, and negativelyto the biomass of larvaceans, but in the smallest species growthwas unrelated to these factors. However, because the variabilityin these two factors within microcosms exceeded their naturalrange of variability, growth rates of larvaceans may normallybe unlimited by resources or population density effects. ¹Present address :Monterey Bay Aquarium Research Institute 7700Sandholdt Road, Moss Landing, CA 95039-0628, USA ²Present address :Bedford Institute of Oceanography PO Box 1006,Dartmouth, Nova Scotia B2Y 4A2, Canada     

Copepod egg production, moulting and growth rates, and secondary production, in the Skagerrak in August 1988

Measurements of hydrography, chlorophyll, moulting rates ofjuvenile copepods and egg production rates of adult female copepodswere made at eight stations along a transect across the Skagerrak.The goals of the study were to determine (i) if there were correlationsbetween spatial variations in hydrography, phytoplankton andcopepod production rates, (ii) if copepod egg production rateswere correlated with juvenile growth rates, and (iii) if therewas evidence of food-niche separation among co-occumng femalecopepods The 200 km wide Skagerrak had a stratified water columnin the center and a mixed water column along the margins. Suchspatial variations should lead to a dominance of small phytoplanktoncells in the center and large cells along the margins; however,during our study blooms of Gyrodinium aureolum and Ceratium(three species) masked any locally driven differences in cellsize: 50% of chla was >11 µm, 5% in the 11–50µm fraction and 45% <50 µm. averaged for allstations. Chlorophyll ranged from 0.2 to 2.5 µg l^–1at most depths and stations. Specific growth rates of copepodsaveraged 0.10 day^–1 for adult females and 0.27 day^–1for juveniles The latter is similar to maximum rates known fromlaboratory studies, thus were probably not food-limited. Eggproduction rates were food-limited with the degree of limitationvarying among species: 75% of maximum for Centropages typicus, 50% for Calanus finmarchicus, 30% for Paracalanus parvus and 15% for Acartia longiremis and Temora longicornis. Thedegree of limitation was unrelated to female body size suggestingfood-niche separation among adults. Copepod production, summedover all species, ranged from 3 to 8 mg carbon m^–3day^–1and averaged 4.6 mg carbon m^–1 day^–1. Egg productionaccounted for 25% of the total.     

Vertical distribution, life cycle and production of the chaetognath Sagitta crassa in Tokyo Bay, Japan

The daytime vertical distribution of Sagiita crassa in TokyoBay was examined from February 13, 1988 to February 20, 1989.High densities of larger-size chaetognaths were found near thesea bottom, whereas the smaller animals tended to inhabit theupper layers. This feature of distribution is discussed in relationto the distribution of their main food organisms, e g. Pseudodiaptomusmarinus, Acartia omoru, Centropages abdomialis and Oithona davisae.The two periods of replacement of two morphs were confirmedby the variation only in mean body length of this chaetognath,unlike the previous authors who made additional morphologicalobservations. It was hypothesized that S.crassa has at leastfive generations Two generations, including mostly the largerforms, had higher growth rates than the generation consistingmainly of the small form. Yearly respiration of S.crassa was8.2 g C m^–Abstract. Yearly production of this animal wasestimated to be 3.8 g C m^–. A feeding estimate revealedthat chaetognaths require a prey production of 13.1 g C m^–year^–1. The impact of this chaetognath on the prey populationin Tokyo Bay and the propriety of an estimated value of annualproduction of S crassa is discussed.