Zooplankton in the Vasikkalampi pond, a warm water effluent recipient in Central Finland

Seasonal and vertical fluctuations of zooplankton species composition,biomass, and production were monitored by weekly sampling duringa two year period in one eutrophic pond in Central Finland.The study was one part of a more comprehensive study programto investigate the effects of warm water effluents from onesmall thermal power plant (35 MW) on the pond ecosystem. Becauseof the circulation of the pond water through the pumps in thepower plant the crustacean populations were very sparse in planktonduring the seasons the power plant was in operation (late Augustto May). During that time rotifers were dominant and some speciesreached very high densities (e.g., Keratella cochlearis s.l.ca. 15 000 ind. l^–1 in sping). In summer months Asplanchnapriodonta, Ceriodaphnia quadrangula, Bosmina longirostris, Mesocyclopsleuckarti and Thermocyclops oithonoides were dominant. A totalof 96 planktonic and meroplanktonic taxa were identified (26ciliates, 46 rotifers, 21 cladocerans and 3 copepods). The dryweight biomass of total zooplankton was 10 mg m^–3 in wintermonths, 10–100 mg m^–3 in spring and 300–1000mg m^–3 in summer. The total yearly production of zooplanktonwas 8552 mg dry wt m^–3 a^–1 in 1979 and 8440 mg drywt m^–3 a^–1 in 1980, from which the proportion ofrotifers was 33–39%, cladocerans 52–58% and copepods8.6 –9.4%. The winter production was 0.2–0.5% ofthe total yearly production, that of spring and autumn togetherwas 8.1–10.4% and the remainder (89–91%) was summerproduction.     

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,     

Biogeographic study of the planktonic communities of the Prince Edward Islands (Southern Ocean)

Microphytoplankton and zooplankton composition and distributionin the vicinity of the Prince Edward Islands and at the Sub-antarcticFront (SAF) were investigated in late austral summer (April/May)1996. Samples were collected for analysis of chlorophyll a concentration(Chi a), microphytoplankton and zooplankton abundance. Generally,the highest Chl a concentrations (up to 2.0 µg l^–1)and zooplankton densities (up to 192 ind. m^–3) were recordedat stations within the inter-island area while the lowest values(<0.4 µg l^–1) were observed at stations upstreamof the islands. High Chl a and zooplankton biomass values werealso associated with the SAF. Microphytoplankton were dominatedby chain-forming species of the genera Chaetoceros (mainly C.neglectus),Fragilariopsis spp. and the large diatom Dactyliosolen antarcticus.The zooplankton assemblages were always dominated by mesozooplanktonwhich at times contributed up to 98% of total zooplankton abundanceand up to 95% of total biomass. Among mesozooplankton, copepods,mainly Clausocalanus brevipes and Metridia lucens numericallydominated. Among the macrozooplankton euphausiids, mainly Euphausiavallentini, E.longirostis and Stylocheiron maximum, and chaetognaths(Sagitta gazellae) accounted for the bulk of abundance and biomass.Cluster and ordination analysis did not identify any distinctbiogeographic regions among either the microphytoplankton orzooplankton.     

Zooplankton composition and distribution off the coast of Galicia, Spain

During June and September 1984, zooplankton samples were collectedwith other hydrographic and biological data along the Galiciancoast (NW of Spain). In June copepods contributed {small tilde}60%to the total zooplankton community, with larvaceans, siphonophoresand cladocerans also abundant. In September >90% of the zooplanktonsampled were copepods. The dominant species of copepods in bothJune and September were Acartia clausi, Paracalanus parvus andTemora longicornis. The meroplankton was dominated by echinoderms,bryozoans, barnacle larvae and bivalve larvae. In June the averagezooplankton biomass was 31.08 mg C m^–3; the Septemberaverage was 41.69 mg C m^–3. The relationship between theslopes of the regression equations (biomass versus abundance)suggests that the zooplankton assemblage in June was composedby larger animals than in September. The major concentrationof zooplankton was between 0 and 50 m, with both June and Septemberdaytime surface samples having 6–7 times the amount oforganisms than the lower water column (50–100 m). Therewere no distinct differences in total zooplankton abundancesat the inshore and offshore stations; however, the inshore stationsoften had a higher percentage of meroplankton than the offshorestations. In June zooplankton abundance at the northern transectsand the western transects was similar. In September there weregreater concentrations of zooplankton in the western Galicianshelf as compared with the northern shelf. These differencesin the horizontal distribution of the zooplankton were relatedto upwelling events.     

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.     

Abundance and diversity of surface zooplankton in the Gulf of Aqaba, Red Sea, Egypt

Surface zooplankton were studied in Egyptian coastal watersof the Gulf of Aqaba, from bimonthly samples from July 1994to May 1995. Species diversity, numerical abundance and dynamicswere analysed for each taxon, at six sites, inside three Protectorates.A total of 62 taxa and species were identified. At all sites,copepods were predominant in the standing crop with an averageof 1945 ind. M^–3 and formed {small tilde}75.5%, numerically,of the total zooplankton community. The meroplanktonic larvaeoccupied the second rank and they constituted {small tilde}19.7%of the total zooplankton. Seasonally, the main peak of zooplanktonabundance was recorded in winter (January) with an average of3510 ind. M^–3 while September was characterized by thelowest density (1906 ind. m^–3 The relatively higher diversityvalues were recorded at Ras Mohammed Protectorate and a progressivedecline in diversity was observed northward.     

Distribution of Calanus species in Kongsfjorden, a glacial fjord in Svalbard

The distribution of Calanus species was investigated in Kongsfjordenin summer of 1996 and 1997. In both years Calanus finmarchicusand Calanus glacialis dominated, although the boreal C. finmarchicuswas more abundant than the Arctic C. glacialis in 1997. Thiscoincided with a 2°C higher water temperature at 50 m in1997, indicating stronger influence of Atlantic origin waterthat year. Advected Calanus finmarchicus occurred in deep andsubsurface layers of the outer fjord in 1996 (200 ind. m^-3,mainly CIII). A less abundant local population aggregated insurface layers of the inner fjord (100 ind. m^-3). Similarly,advected C. finmarchicus occurred in subsurface layers in 1997(446 ind. m^-3, mainly CIII and CIV) and a local population insurface layers (183 ind. m^-3, mainly CI). Calanus glacialisin 1996 aggregated as CII and CIII in the deep layers of theouter fjord (272 ind. m^-3), whereas CIII–CV were abundant(216 ind. m^-3) in cold surface waters of the inner fjord. In1997 C. glacialis (mostly CIII–CV) was more abundant inthe outer than in the inner part of the fjord (40 and 192 ind.m^-3, respectively). Within Kongsfjorden, Calanus finmarchicusneeds one year to complete its life cycle, whereas Calanus glacialisneeds two. Calanus hyperboreus seems to be an expatriate inthe fjord system.     

Primary and bacterial production compared to growth and food requirements of Daphnia longispina in Lake Kvernavatnet, west Norway

Primary production, and bacterial production as measured byincorporation of [³H-methyl]thymidineinto ice cold TCA insolublematerial were investigated during 1984 in Lake Kvernavatnet,west Norway. Primary production averaged 222 mg C m^–2day^–1 and bacterial production averaged 163 mg C m^–2day^–1. The bacterial production in the euphotic pelagiczonecontributed -60% of the total pelagic bacterial production.The zooplankton was dominated byDaphnia longispina. From growthexperiments with animals fed only natural food in coarse filteredlake water, the population daily growth increments were calculated.The average production of D.longispina was 151 mg C m^–2day^–1 during the period investigated. The estimated primaryproduction was too low to sustain both the bacterial productionand the zooplankton food requirements. These results imply thatthe carbon cycle of the lake is dependent on the supply of allochtonousmaterial, or that the current methods for measuring productionrates in aquatic environments are systematical erratic.     

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.     

Trophodynamics of the scyphomedusae Aurelia aurita. Predation rate in relation to abundance, size and type of prey organism

Ephyra larvae and small medusae (1.7–95 mm diameter, 0.01–350mg ash-free dry wt, AFDW) of the scyphozoan jellyfish Aureliaaurita were used in predation experiments with phytoplankton(the flagellate Isochrysis galbana, 4 µm diameter, {smalltilde}6 x 10^–6 µg AFDW cell^–1), ciliates (theoligotrich Strombidium sulcatum, 28 µm diameter, {smalltilde}2 x 10^–3 µg AFDW), rotifers (Synchaeta sp.,0.5 µg AFDW individual^–1) and mixed zooplankton(mainly copepods and cladocerans, 2.1–3.1 µg AFDWindividual^–1). Phytoplankton in natural concentrations(50–200 µg C I^–1) were not utilized by largemedusae (44–95 mm diameter). Ciliates in concentrationsfrom 0.5 to 50 individuals ml^"1 were consumed by ephyra larvaeand small medusae (3–14 mm diameter) at a maximum predationrate of 171 prey day^–1, corresponding to a daily rationof 0.42%. The rotifer Synchaeta sp., offered in concentrationsof 100–600 prey I^–1, resulted in daily rations ofephyra larvae (2–5 mm diameter) between 1 and 13%. Mixedzooplankton allowed the highest daily rations, usually in therange 5–40%. Large medusae (>45 mm diameter) consumedbetween 2000 and 3500 prey organisms day^"1 in prey concentrationsexceeding 100 I^–1. Predation rate and daily ration werepositively correlated with prey abundance. Seen over a broadsize spectrum, the daily ration decreased with increased medusasize. The daily rations observed in high abundance of mixedzooplankton suggest a potential ‘scope for growth’that exceeds the growth rate observed in field populations,and this, in turn, suggests that the natural populations areusually food limited. The predicted predation rate at averageprey concentrations that are characteristic of neritic environmentscannot explain the maximum growth rates observed in field populations.It is therefore suggested that exploitation of patches of preyin high abundance is an important component in the trophodynamicsof this species. ¹Present address: University of Bergen, Department of MarineBiology, N-5065 Blomsterdalen, Norway     

Isolation, Culture, and Plant Regeneration of Protoplasts of Two Shrubby Oxalis Species from South America

Protoplasts were successfully isolated from internodal callustissues of both Oxalis glaucifolia and O. rhombeo-ovata whenthey were digested in a solution containing 0.1% (w/v) MacerozymeR-10, 0.5% (w/v) cellulase Onozuka R-10 and 0.3 mmol m^–3sucrose. Protoplasts proliferated to give cell colonies on Gamborget al.'s B5 medium supplemented with 0.3 mmol m^–3 mannitol,0.5 mg dm^–32, 4-D, and 2.0 mg dm^–3 kinetin. Calluswas produced upon transfer of cell colonies to Murashige andSkoog medium containing 2.0 mg dm^–3 l-naphthaleneaceticacid (NAA) and 0.1 mg dm^–3 kinetin for O. glaucifolia,or with 5.0 mg dm^–3 NAA and 0.5 mg dm^–3 6-benzylaminopurine,for O. rhombeo-ovata. Plants were regenerated from O. glaucifoliaprotoplasts on a medium containing 0.1 mg dm–3 NAA, 1.0mg dm^–3 kinetin and 1.0 mg dm^–3 gibberellic acid,but only vascular nodules were differentiated by O. rhombeo-ovataprotoplast-derived calli. Key words: Tissue culture, protoplasts, plant regeneration, Oxalis spp     

The contribution of ammonia excreted by zooplankton to phytoplankton production in Narragansett Bay

Ammonia excreted by mixed zooplankton populations over an annual(1972–1973) cycle in Narragansett Bay varied from 0.04to 3.21 µg at NH₃-N dry wt^–1 day^–1, exclusiveof two exceptional rates measured one year apart: 11.74 and18.39 µg at NH³-N mg dry wt^–1 day^–1. Grossphytoplankton production integrated over the year (1972–1973)averaged 151 mg C m^–3 day^–1 for an 8 m water column;peaks of 332 and 905 mg C m^–3 day^–1 occurred duringthe winter-spring and summer blooms, respectively. Excretedammonia, integrated seasonally and annually, contributed only0.2% and 4.9% of the nitrogen required for observed gross productionduring the winter-spring and summer blooms, respectively, and4.4% annually. However, excreted ammonia may be an importantsource of the nitrogen required by Skeletonema costatum, thedominant diatom in Narragansett Bay, during the post-bloom periodwhen 186% of the nitrogen required for its net production wasmet by ammonia excretion. A combination of zooplankton ammoniaexcretion and benthic ammonia flux contributed 22% of the nitrogenrequired for the annual gross production (440 g C m^–2)while 51% of the nitrogen required for the net production ofSkeletonema was accounted for by regenerated nitrogen. ¹This research was supported by NSF grant GA 31319X awardedto Dr.T.J.Smayda.     

Annual pattern of micro- and mesozooplankton abundance and biomass in a subtropical estuary

The pattern of biomass and abundance of microzooplankton andmesozooplankton were studied over an annual cycle in the NuecesEstuary, Texas. Zooplankton samples and associated hydrographicdata were collected at four locations at biweekly intervalsfrom September 1987 through October 1988. This is a broad, shallowbay system with an average depth of 2.4 m. The concentrationof chlorophyll a in the surface waters averaged 7.4 µgl^–1with 85% passing through a 20 µ mesh. Microzooplankton(20–200 µ in length) were extremely abundant throughoutthis study. Abundances of ciliates (including both aloricateciliates and tintinnids) ranged from 5000 to 400 000 l^–,with a mean of 38 000 l^–1 of seawater over the entirecourse of the study. Mesozooplankton (200–2000 µmin length) abundance averaged 6100 m^–3 for samples collectedduring the day and 10 100 m^–3 for samples collected atnight. Mesozooplankton were dominated by Acartia tonsa whichmade up {small tilde}50% of the total. Biomass estimates formicrozooplankton (based on volume estimates) were often higherthan measured biomass of mesozooplankton. Given the shortergeneration times and higher metabolic rate of microzooplanktoncompared to mesozooplankton, microzooplankton should have agreater effect on the trophic dynamics of the Nueces Estuarythan mesozooplankton.     

Chemical composition and biomass parameters of a population of Craspedacusta sowerbii Lank1880 (Cnidaria: Limnomedusa)

Until now, very little information about the ecology of thefreshwater jellyfish, Craspedacusta sowerbii, has been available.Although many publications deal with Craspedacusta, most ofthem contain only observations. Detailed analyses are rare.In this study, investigations on size-dependent fresh and dryweights, and carbon, nitrogen and phosphorus, are presented.The water content of the medusae ranged between 96.74 and 99.87%.Fresh and dry weights ranged from 0.06 to 331.86mg FW ind.^0–1and 0.01 to 2.50 mg DW ind.^–1, respectively. The molarC:N:P relationship was calculated as 39:9:1. The C:P ratio waslow in contrast to other freshwater zooplankton species, andimplied a high demand for P. A comparison with the C:P stoichiometryof their prey indicates the possibility of P limitation of Craspedacustaat a gross growth efficiency above 25%. The results are discussedin relation to medusae abundance, bioaccumulation and theirimpact on food web structure.     

Hydrodynamic Control of Late Summer Species Composition and Abundance of Zooplankton in Hudson Bay and Hudson Strait (Canada)

The spatial variation in zooplankton biomass, abundance andspecies composition in relation to hydrography and chlorophylla (Chl a) was studied in the subarctic waters of Hudson Bayand Hudson Strait. Sampling was carried out in early September1993 at 21 stations arranged along a transect following theQuébec coast from James Bay, in Hudson Bay, to the vicinityof Ungava Bay in Hudson Strait. Both the biomass and the abundanceof total zooplankton were low along the lower part of HudsonBay (averaging 1.6 g DM m^–2 and 9432 ind. m^–2) andincreased sharply toward the upper end of the Bay and in HudsonStrait (averaging 6.0 g DM m^–2 and 40 583 ind. m^–2).A total of 80 zooplankton taxa was identified in the samples.Copepods were clearly numerically dominant at all sampling stations,accounting for more than 85% and 93% of the zooplankton communityin the Bay and the Strait, respectively. Clustering samplesby their relative species composition revealed four groups distributedalong well defined environmental gradients characterizing thedistribution of physical variables and Chl a. The first group,located in the most southern region of Hudson Bay and fartheroffshore, northwest of the Belcher and Sleeper Islands, wasstrongly influenced by freshwater run-off from James Bay andother major rivers around the Bay, and was characterized bythe presence of two euryhaline copepod species (Acartia longiremisand Centropages hamatus). The second and the third groups occupiedthe largest region along the sampling transect, from the middleof Hudson Bay to the western region of Hudson Strait, and werecharacterized by a typical arctic zooplankton fauna relatedto the cyclonic circulation in central Hudson Bay. The fourthgroup was located in the easternmost part of the sampling transectin Hudson Strait where the highest phytoplankton biomass valueswere observed (Chl a ~220 mg m^–2). The zooplankton assemblagethere showed an important increase in the abundance of the largeherbivorous copepod Calanus glacialis/finmarchicus, which werenumerically four times more abundant in the central Strait region(averaging 15 251 ind. m^–2) than in the western side ofHudson Strait and in Hudson Bay (3629 ind. m^–2). Theseresults support the hypothesis that the structure in the localbiological community is influenced by the local hydrodynamicfeatures which, through their action on surface water temperature,salinity, stratification and mixing conditions, lead to spatialdifferentiation of the phytoplankton and zooplankton communities.     

DISTRIBUTION AND ABUNDANCE OF GYMNOSOMATA (GASTROPODA: OPISTHOBRANCHIA) IN THE SOUTHWEST ATLANTIC

The distribution and abundance of gymnosome gastropods in theArgentine Sea and Brazil—Malvinas Confluence during 1978–1979and 1988 were studied. The collections analyzed included 768quantitative samples obtained between 48°W and the coast,and from 35°S to 55°S. Two species were found. Spongiobranchaeaaustralis was the most frequent and abundant (up to 730 per1000 m3); its presence in the area was associated with the coreof the Malvinas Current. Clione antarctica was less abundant(maximum abundance: 230 per 1000 m³) and was also associatedwith the Malvinas Current. The geographic ranges of both speciesin the area are wider than previously described. Since the rangeof S. australis in the area extends far from the range of itsprey Clio, it is not clear whether S. australis can feed onthe thecosomatous pteropod Limacina (and not only on Clio, asdescribed in the bibliography) or it starves in that area. Duringthe 1978–1979 annual cycle, the abundance of both speciesfollowed neither the abundance patterns of their prey nor ofthe total zooplankton, and differed from each other. The residencetime of swarms of both gymnosomes were shorter than one month.As a general pattern, the aggregates are rapidly transportednorthward by the Malvinas Current and also penetrate the outershelf water, but they remain there only during a short periodand cannot preclude the final expatriation. So, the abundanceof gymnosomes in the area depends on passive migration morethan intrinsic population factors. (Received 9 July 1997; accepted 15 December 1997)     

The Zooplankton community of Croker Passage,Antarctic Peninsula

Summary Zooplankton species composition, abundance and vertical distribution were investigated in the upper 1000 m of Croker Passage, Antarctic Peninsula during the austral fall (March–April, 1983). 106 species were identified, many being mesopelagic and reported previously from the Southern Ocean. The most numerous species (>1000/100 m³) were the copepodsMetridia gerlachei, Microcalanus pygmaeus, Oncaea antarctica andOncaea curvata. Oncaea curvata alone constituted half the zooplakton population. Zooplankton biomass was dominated by three copepod species,Metridia gerlachei, Calanoides aculus andEuchaeta antarctica,which comprised 74% of the biomass. Size analysis revealed most of the zooplankton numbers were in the >1 mm fraction. The biomass distribution was polymodal with major maxima in the >1 mm and the 4–4.9 mm size classe. The >1 mm peak, exclusive of protozoans, was primarily copepod nauplii and copepodites ofOncaea, Metridia andMicrocalanus. The 4–4.9 mm peak was mostlyCalanoides acutus andMetridia gerlachei.All of the principal species had broad vertical distributions both day and night. There was some suggestion of diel vertial migration byMetridia gerlachei andEuchaeta antarctica, with segments of their populations migrating into the upper 100 m and 200 m, respectively, at night. Most of the dominant and subdominant species were concentrated below 200 m,with only the subdominantOithona similis having its maximum in the epipelagic zone. The occurrence of zooplankton at winter depths appears to have been earlier in Croker Passage in 1983 than has been generally reported for waters south of the Polar Front.Total standing stock of net-caught zooplankton (>15 mm) in the upper 1000 m was estimated at 3.1 gDW/m², which is somewhat higher than values reported for the West Wind Drift and for open ocean areas of temperate to tropical latitudes.Euphausia superba (17–52 mm) dominated the pelagic biomass, exceeding zooplankton standing stock under a square meter of ocean by a factor of 15. This is in contrast to lower latitudes where zooplankton biomass is usually greater than macrozooplankton-micronekton.     

The ecology of the Calanus ponticus population in the deeper layer of its concentration in the Black Sea

The layer of daytime concentration of Calanus ponticus (VC andVI C) performing daily vertical migrations and the layer of‘winter stock’ aggregation are confined to the depthof maximal gradient of the main pycnocline under an unusuallysharp oxycline. The concentration layer thickness ranges from2 to 20–30 m and the Calanus concentration in it is >250ind. m^–3, sometimes being 3500 ind. m^–3 and evenmore. The population in the concentration layer is divided intotwo ecological groups: I, feeding and migrating specimens ofcopepodite stages V and VI, their body lipid contents being25–60 µg min.^–1; and II, non-feeding and non-migratingspecimens of copepodite stage V, their body lipid contents being100–150 µg ind.^–1. The relationship with oxygenconcentration was studied in both ecogroups. The experimentsshow that specimens of ecogroup II can exit at an oxygen concentrationof 0.06 ml 1^–1, but at such concentration falling intoanabiosis. They die at 0.04 ml O₂ 1^–1. Estimates of respirationof the group II specimens (‘winter stock’) showthat lipids they store are sufficient for 7 months' survival.Depth of Calanus concentration is determined by water densityrather than concentration of oxygen.     

Predation and respiration by the small cyclopoid copepod Oithona similisr: How important is feeding on ciliates and heterotrophic flagellates?

Feeding on natural plankton populations and respiration of thesmall cyclopoid copepod Oithona similis were measured duringthe warm season in Buzzards Bay, Massachusetts, USA. AlthoughO.similis did not significantly ingest small autotrophic andheterotrophic flagellates (2–8 µn), this copepodactively fed on >10 µm particles, including autotrophic/heterotrophic(dino)flagel-lates and ciliates, with clearance rates of 0.03–0.38ml animal^–1 h^–1. The clearance rates increased withthe prey size. O.similis also fed on copepod nauplii (mainlycomposed of the N1 stage of Acartia tonsa with a clearance rateof 0.16 ml animal^–1 h^–1. Daily carbon ration fromthe combination of these food items averaged 148 ng C animal^–1day^–1 (41% of body C day^–1), with ciliates and heterotrophicdino-flagellates being the main food source ({small tilde}69%of total carbon ration). Respiration rates were 020–0.23µl O₂ animal^–1 day^–1. Assuming a respiratoryquotient of 0.8 and digestion efficiency of 0.7, the carbonrequirement for respiration was calculated to be 125–143ng C animal^–1 day^–1, close to the daily carbon rationestimated above. We conclude that predation on ciliates andheterotrophic dinoflagellates was important for O.similis tosustain its population in our study area during the warm season.