The nature of zooplankton spatial heterogeneity in a nonriverine impoundment

Knowledge of spatial heterogeneity characteristic of reservoir plankton communities is fundamental to a variety of ecological studies. Degree of spatial heterogeneity in the zooplankton community of Center Hill Reservoir, with water residence times of 50–250 days, was positively correlated with rate of water influx. Important spatial differences resulted from the contrast between zooplankton associated with new and longer-impounded water. The nature of spatial heterogeneity differed fundamentally from the more riverine impoundments where spatial differences are often persistent and characterized by gradual change (as opposed to contrast) in plankton assemblages with respect to location. Magnitude of plankton spatial heterogeneity in nonriverine impoundments may be predictable from inflow rates. Areas, between which major differences in plankton communities exist, may also be definable from knowledge of inflow dispersal patterns in these impoundments.     

Influence of river inflows on plankton distribution around the southern perimeter of the Salton Sea,California

The influence of river inflows (2.5–5 g l⁻¹) on phytoplankton and zooplankton was assessed with samples collected at 17 sites around the 50 km perimeter of the southern basin of the Salton Sea (41–45 g l⁻¹) along the 5 m isobath on 2 September and 11 December 2000. Phytoplankton generally increased in abundance downcurrent of the points of inflow, but patterns in downcurrent abundance varied widely among species. Several diatom species showed large increases; Chaetoceros muelleri var subsalsum, Cylindrotheca closterium and Thalassionema sp. increased up to 800-fold in abundance by ca. 20 km downcurrent from inflow points in September. In contrast, the dinoflagellates Gyrodinium uncatenum and Prorocentrum minimum increased 6- and 4-fold, respectively, in December, and Gonyaulax grindleyi actually decreased downcurrent of the rivers in September. In September, patterns in downcurrent abundance were correlated with the ratio of cell surface area to cell biovolume, with species with high ratios showing the largest increases. Zooplankton abundances did not show regular trends downcurrent of river inflows except for the larvae of Balanus amphitrite, which increased in density ca. 100-fold. This increase most likely reflected the abundance of adult-colonized rocky substrates near river inflow points. The strong upcurrent trends documented for some species seemed to have been due to the injection of nutrient-rich water from central to nearshore areas and near-site mortality due to the presence of hydrogen sulfide. This study gives a first glimpse of the complexity of the responses of nearshore plankton to river inflow and provides evidence for how changes in factors such as current speed, nutrient supply and salinity stratification may influence plankton dynamics. Guest Editor: John M. Melack Saline Waters and their Biota     

Plankton development in a rapidly flushed lake in the River Spree system (Neuendorfer See, Northeast Germany)

The Neuendorfer See is a shallow lake through which the RiverSpree flows. In the lake, abundances of zooplankton (mainlyrotifers) and phytoplankton increased exponentially over theflowing stretch between the inflow and the outflow of the river.Increase in space is enhanced by increased residence time inthe lake. Sensitivity of plankton development on residence timesof >8 days weakened at longer residence times. This patternholds for all zooplankton species. Rates of change in chlorophylland rotifers (after correction for temperature) are first enhanced,then are decreased at longer residence times. Concentrationsof dissolved inorganic nutrients [Si, soluble reactive phosphorus(SRP) and NO₃–] and the N/P ratio diminished with increasingresidence time. The plankton dynamics in the lake were dependenton discharge and the lake behaved as a ‘plug flow tubularreactor’ with minor longitudinal mixing. This was notdifferent from the transportation in large rivers.     

Association of the gonyaulacoid dinoflagellate Alexandrium ostenfeldii with spirolide toxins in size-fractionated plankton

Spirolides are pharmacologically active macrocyclic imines discoveredin shellfish and plankton size-fractions collected from near-surfacewaters along the southeastern coast of Nova Scotia (NS), Canada.These compounds are most prevalent in the water column withinplankton size-fractions from 21 to 56 µm during late spring.Analysis of bulk plankton material by liquid chromatographycombined with ion-spray mass spectrometry indicated that gonyaulacoiddinoflagellates were domin-ant members of the plankton assemblagein these fractions when spirolides were abundant at Graves Shoal,NS, but that spirolides disappeared from the water column aftera shift to diatom dominance. Spirolide composition in the planktonwas rather consistent over time and among different sizefractionswithin a site, but the profile was radically different betweensites in Nova Scotia. At Ship Harbour, NS, spirolides A, B,C and desmethyl-C were the major constituents, whereas at GravesShoal, the primary spirolide derivatives were B, D and an isomerD2. Correlation analysis of spirolide abundance and the occurrenceof particular taxa in size-fractionated plankton showed thatthe highest correlations were with Alexandrium species (r² =0.93) and GB42 cells (r² = 0.83). These latter cells are nowrecognized as athecate forms of gonyaulacoid dinoflagellates,primarily of Alexandrium ostenfeldii. By analysis of size-fractionatedplankton and comparison with cultured plankton isolates fromspirolide-rich areas, we have substantiated the primary roleof A. ostenfeldii as the source of spirolides in the water column.     

广东长潭水库浮游生物群落结构特征

长潭水库是广东梅州市重要的备用水源地,属于国家一类水源保护区。2010年7月,通过分析长潭水库浮游生物群落组成、生物量及多样性指数等群落结构特征和水体理化指标,揭示长潭水库富营养化水平。结果显示,长潭水库鉴定出55种浮游植物,隶属于6个门,优势种为绿藻门的栅藻（Scenedesmus sp.）、蓝藻门的微囊藻（Microcystis sp.）和伪鱼腥藻（Pseudanabaena sp.）、隐藻门的隐藻（Cryptophyta sp.）以及硅藻门的小环藻（Cyclotella sp.）和针杆藻（Synedra sp.）;藻类密度范围1.71×10⁶~2.44×10⁸ cells/L;浮游动物共检出44种,包括轮虫、枝角类和桡足类,其中轮虫是主要类群。综合营养状态指数评价结果显示,长潭水库部分水体呈轻度富营养化。典范对应分析结果显示,浮游动物、溶解氧、总氮、总磷和化学需氧量是影响长潭水库浮游植物群落结构的关键环境因子。     

The influence of water exchange on zooplankton dynamics and species development in a south Norwegian fjord

During experiments in a south Norwegian fjord in March and April1979, distribution and development of zooplankton were investigatedin detail. Numbers of protozooplankton, meroplankton and holoplanktonwere determined as individual species. Strong water exchangecaused a high variability in plankton composition and biomass.Changes in salinity and temperature as well as numbers of planktonindividuals and in the percentage composition of the developmentalstages of the spring spawning Calanus finmarchicus revealedthat a wind-induced inflow of Skagerrak water along the southwestNorwegian coast also entered the Rosfjord. In contrast to theAtlantic water with low numbers of copepods from the hibernatinggeneration, in the Skagerrak water the spring generation ofC.finmarchicus had already developed up to the first and secondcopepodite stages. The Skagerrak water was already very richin phyto- and zooplankton organisms. Here, an increase in biomassover time mainly resulted from the development of younger toolder copepodite stages and from a considerable increase innumbers of the tintinnid, Leprotintinnus pellucidus. The verticaldistribution of plankton organisms and fecal pellets was closelyassociated with the occurrence and the stratification of watermasses coming into the Rosfjord.     

Nutrients,Conductivity and Plankton in a Landscape Approach to a Pampean Saline Lowland River (Salado River,Argentina)

Nutrients, conductivity and other physical and chemical parameters were measured seasonally in the main channel and in tributaries of the Salado River basin during the period March 1997–June 1999. The sampling began in a low water period and later included flood events. High water events were associated with high proportions of allochthonous compounds (polyphenols, suspended solids and organic matter). Nutrients and conductivity were related to hydrological conditions and different land uses in the catchment. A relationship was found between the land-use and nutrient concentrations due to the inflow of diffuse sources from agricultural lands. High nutrient concentrations and conductivity recorded in the headwaters were, respectively, related to the intensive agriculture in this area and the inflow of saline groundwater, drained by canals from endorheic basin to the main channel. Their effects on the middle and lower reaches were related to the discharge and inputs of other sub-catchments. Nutrients, sulphates, alkalinity and conductivity declined downstream towards the river mouth. The consequences for the plankton community of these spatio-temporal changes in the chemical characteristics are discussed. The heterogeneity of the Salado River is related to seasonality, land use and the geomorphological features of the basin.     

Distribution of potentially pathogenic bacteria as free living and plankton associated in a marine coastal zone

AIMS: To determine the abundance of faecal and nonfaecal bacteria related to human and animal health, as free living or associated with small (>64 microm) and large (>200 microm) plankton, samples were collected monthly from the coastal zone at Messina (Italy). METHODS AND RESULTS: Different enrichment and selective cultural methods were used to determine the abundance of bacteria in sea water and plankton. The bacteria were more frequently isolated from water and large plankton than from small plankton. Vibrio and Aeromonas spp. showed different distribution patterns in water and plankton. Faecal indicators were always present in water and the large size class plankton samples. Enterococci associated with large plankton were more abundant than E. coli in the winter. Vibrio species distributions were different in water and plankton samples. Among arcobacters only A. butzleri was isolated from water and plankton samples. Campylobacter spp. was always absent in small plankton and more frequent in large plankton than in water. CONCLUSIONS: The colonization of zooplankton by potentially pathogenic bacteria is a widespread phenomenon. SIGNIFICANCE AND IMPACT OF THE STUDY: The presence of potentially pathogenic bacteria in sea water and associated with plankton can have ecological and epidemiological implications.     

Phosphorus release and sedimentation in three contiguous shallow brackish lakes, as estimated from changes in phosphorus stock and loading from catchment

In situ phosphorus release rates in three contiguous shallow brackish lakes were calculated by considering the amount of water inflow, changes in salinity and phosphorus stock, and loading from phosphorus inflow based on monthly data. The annual amount of sedimental phosphorus relative to that of phosphorus inflow was different for each of the three water bodies: 16% for Lake Shinji, 3% for the Honjo area, and −8% for Lake Nakaumi, as estimated in a 10-year period from January 1993 to December 2002. During the warm season, the quantity of phosphorus released surpassed sedimentation in these three water bodies. The low annual sedimentation ratio in Lake Nakaumi is related to a large seawater backflow resulting in phosphorus removal, in addition to a stable stratified structure promoting phosphorus release from sediment due to oxygen depletion in the lower layer. In Lake Nakaumi, field data shows that if dissolved oxygen at the sediment surface falls below 2.54 mg L⁻¹, phosphorus release from the sediment begins to be accelerated.     

Horizontal distribution of crustaceans in Lake Glubokoe

A study has been made on the distribution of crustaceans along a profile of 6–9 stations from depths of less than 2 m to 20 m, in summer, autumn and early spring. The species composition, abundance, size-frequency distribution, biomass and diurnal dynamics were estimated. Many species abundant in the pelagic zone were found to be absent or scarce out to depths of 5 m. In the daytime, at depths out to 3 m, crustaceans greater than 1.0 mm were seldom found, while those 0.15–0.40 mm long were most abundant. At depths out to 5 m, not only was the total average size of crustaceans found to be smaller, but also that of individual species, including small ones: Ceriodaphnia and Chydorus. The biomass of crustaceans in shallow water and in the open lake differs in summer by more than 100 times, and in late autumn and early spring by more than 10 times. At the depth of 1 m, in none of the seasons did it exceed 0.026 mg l^-1. All the crustaceans except for nauplii and Chydorus considerably increased in numbers in the shallow water at night. The impoverishment of the littoral plankton in Lake Glubokoe is regarded as a specific case of the well-known phenomenon of ‘avoidance of the littoral’ by euplankton (Hutchinson, 1967; Kiselyov, 1980). It is pointed out that there is a possible relationship between diurnal horizontal migrations of plantivorous fish and the impoverishment of plankton near the shore. An attempt has been made to substantiate the assumption that the ‘avoidance of the littoral’ by pelagic crustaceans is due to high numbers of fish in shallow water.     

Changes in plankton and fish larvae communities across hydrographic fronts off West Greenland

The variability in plankton community structure was studiedin Disko Bay and across important fishing banks off the westcoast of Greenland. The primary goal of the study was to investigatepossible linkages between hydrographical processes and planktonstructures, hypothesizing that hydrographic fronts would bepresent in the area, and that these to a large extent determineplankton distribution, composition and productivity. We sampledalong four cross-shelf transects, one covering Disko Bay andDisko Bank, while the other three covered Store Hellefiske Bank,Lille Hellefiske Bank and Sukkertop Bank. The hydrography wasexamined by CTD profiling, the phytoplankton by fluorescenceprofiling and water bottle sampling, while mesozooplankton andichthyoplankton were sampled by vertical or oblique net hauls,respectively. We observed distinct along-shelf flowing currentsin the area (e.g. the West Greenland Current, the Polar Currentand the Irminger Current), and the physical characteristicsindicated frontogenesis at the shelf slope, in regions of 80–100m water depth. Phytoplankton and ichthyoplankton showed a cross-shelfstructuring with apparent linkages to frontal characteristics,while a more diverse pattern was observed for the mesozooplanktonwhich were dominated by Calanus finmarchicus, Calanus glacialisand Calanus hyperboreus. The relationship between hydrographiccharacteristics and plankton distribution differed among species,and apparently specific plankton communities were establishedin different areas of the shelf. For example the larvae of Boreogadussaida, Ammodytes sp., Reinhardtius hippoglossoides and Stichaeuspunctatus differed markedly in distributional characteristics.In addition to the cross-shelf structuring, marked differencesin species composition and total plankton abundance were observedin the along-shelf (north–south) direction. The latitudinaldifferences in the unicellular plankton communities are interpretedlargely within a seasonal successional framework (i.e. an earlydominance of diatoms followed by increasing importance of smallerunicellular plankton), while the ichthyo- and zooplankton communitiesalso differed by the respective dominance of species with polarversus temperate origin. Our findings suggest that the flowof major currents and the establishment of hydrographical frontsare of primary importance to the plankton communities in theWest Greenland shelf area, influencing the early life of fishand the recruitment to the important fisheries resources.     

Species Richness and Invasion Vectors: Sampling Techniques and Biases

During a European Union Concerted Action study on species introductions, an intercalibration workshop on ship ballast water sampling techniques considered various phytoplankton and zooplankton sampling methods. For the first time, all the techniques presently in use worldwide were compared using a plankton tower as a model ballast tank spiked with the brine shrimp and oyster larvae while phytoplankton samples were taken simultaneously in the field (Helgoland Harbour, Germany). Three cone-shaped and 11 non-cone shaped plankton nets of different sizes and designs were employed. Net lengths varied from 50 to 300 cm, diameters 9.7–50 cm, and mesh sizes 10–100 μm. Three pumps, a Ruttner sampler, and a bucket previously used in ballast water sampling studies were also compared. This first assessment indicates that for sampling ballast water a wide range of techniques may be needed. Each method showed different results in efficiency and it is unlikely that any of the methods will sample all taxa. Although several methods proved to be valid elements of a hypothetical `tool box' of effective ship sampling techniques. The Ruttner water sampler and the pump P30 provide suitable means for the quantitative phytoplankton sampling, whereas other pumps prevailed during the qualitative trial. Pump P15 and cone-shaped nets were the best methods used for quantitative zooplankton sampling. It is recommended that a further exercise involving a wider range of taxa be examined in a larger series of mesocosms in conjunction with promising treatment measures for managing ballast water. This revised version was published online in July 2006 with corrections to the Cover Date.     

Trophodynamics of the plankton community at Dogger Bank: predatory impact by larval fish

The trophodynamics of a coastal plankton community were studied,focusing on fish larvae and their copepod prey. The major objectiveswere to describe distributional overlap and evaluate the predatoryimpact by larval fish. The study was carried out across DoggerBank in the North Sea, August-September 1991. Sampling transectscrossed tidal fronts off the Bank and plankton at all trophiclevels showed peak abundance within frontal zones. Also Verticallythere was a significant overlap in distributional patterns ofthe plankton. Seven species of fish larvae were abundant, ofthese sprat (Sprattus sprattus) dominated. The abundance ofone group of fish larvae peaked in the shallow water close tothe Bank, whereas other species, including sprat, were foundin deeper water. Prey preference and predation pressure of fishlarvae were assessed using information on prey sizes and growthrates of larvae and the copepod prey. We estimated larval removalof preferred prey sizes to 3–4% day^–1, counterbalancedby a 3–7% day^–1' replenishment from copepod productionand growth. Additional predation pressure on copepods by aninvertebrate predator was estimated to 1–3%day^–1.In conclusion, the dynamics of fish larvae and other zooplankterswere closely linked. At peak abundances of fish larvae (>35mg dry weight m^–2), the accumulated predation on specificsize ranges of copepods, exerted by larvae and other predators,could exceed the ability of copepod replenishment and intra-/interspecificcompetition among predators might take place.     

Carbon sink to source: longitudinal gradients of planktonic P:R ratios in subtropical reservoirs

Spatial patterns of planktonic production and respiration in the surface mixed layer were examined in eight Texas, USA reservoirs to test the hypothesis that P:R ratios are lowest in upreservoir inflow zones and highest in downreservoir open-water zones, as predicted by the heuristic reservoir zonation model. We measured summer planktonic metabolism with light–dark bottles and physical–chemical conditions in epilimnetic water at 85 sites distributed among sixteen longitudinal transects within the eight reservoirs (2 transects per reservoir). Volumetric production and plankton biomass were lowest in the open-water zones and increased upreservoir; however, that pattern was reversed for areal production due to greater photic depths at open-water sites. Volumetric respiration was similar in the three zones; however, corresponding planktonic P:R ratios in the surface mixed layer were significantly lower at open-water sites, which is opposite than hypothesized. Based on linear regressions of production and respiration rates on chlorophyll a, open-water sites were net heterotrophic during the summer regardless of trophic state; whereas inflow and mid-reservoir zone sites were heterotrophic when chlorophyll concentrations were respectively less than 9.5 and 35?mg?m^?3. Although variation among reservoirs was high, five of the eight reservoirs had inflow zones that were net carbon sinks while seven had open-water zones that were carbon sources. Mean (±standard error) carbon flux rates of inflow, mid-reservoir, and open-water zones were ?0.22?±?0.12 (C sink), 0.39?±?0.44 (moderate C source), and 1.33?±?0.50 (strong C source) g C m^?2 day^?1 respectively. Inflow and mid-reservoir zones comprised approximately 45% of the total reservoir area studied. Therefore, omitting their contribution as often done when a single open-water site is sampled may substantially overestimate reservoir carbon flux.     

The significance of water inputs to plankton biomass and trophic relationships in a semi-arid freshwater wetland (central Spain)

This study attempts to describe changes in plankton biomass(including bacteria, phytoplankton, ciliates, rotifers, andcrustaceans) in the semi-arid, hypertrophic, freshwater wetland,Las Tablas de Daimiel National Park (central Spain), in relationto water inflow. An inter-annual comparison of 1996 and 1997,with contrasting rainfall, reveals that inflows in the formof flooding act as a bottom-up structuring force on total planktonbiomass. However, the responses of plankton biomass to floodingwere different in strength between the two years, which canbe attributed to shifts in plankton community structure. Crustaceanzooplankton conditioned total plankton biomass in 1996, basedon the relationship between the high individual biomass andcommunity development. Crust-aceans decreased in 1997, whilebacteria, phytoplankton and rotifers increased. The quantitativeincrease of the latter groups resulted in a higher total planktonbiomass in 1997. The key position of crustaceans in the wetlandplankton is also reflected in their capability for exertingsignificant top-down control, which was clearly evident in 1996but weaker in 1997, based on their numerical reduction. Statisticalanalyses provide evidence that the decline of trophic interactionsin 1997 is related to the strength of flooding in that year,thereby highlighting the significance of the disruptive actionof physical disturbance on biotic interactions in the plankton.Flooding and areal inundation were also shown to be significantfor spatial heterogeneity. In 1996, site-specific developmenttook place in the absence of prolonged flooding effects, resultingin high spatial heterogeneity. In 1997, however, remarkablehomogenization of plankton biomass occurred along the majorwater flow path. Thus, wetland landscape heterogeneity dependson inflows which condition areal inundation. This, in turn,influences plankton dynamics.     

Plankton in the River Rhine: structural and functional changes observed during downstream transport

The growth dynamics of phytoplankton, zooplankton and bacterioplanktonin the River Rhine were analysed simultaneously with a numberof environmental factors in order to identify environmentalsteering factors and to describe some of their interrelations.Observations on the metabolic activity (for algae and bacteria)and density (for all organisms) were carried Out three timesin 1990 using successive sampling of the same water parcel duringits transport in the lower 660 km reach of the river. High algaldensities (up to 170.5 µg chlorophyll a l^–1), rotifers(up to 1728 l^–1), crustaceans (up to 65 l^–1) andbacteria (up to 16x10⁹ l^–1) were found. Algae and rotifersshowed a rapid successive development during transport, whilecrustaceans were only abundant in the tidal reach of the river.In May, a vigorous growth of phytoplankton, zooplankton andbacteria was found. The diatom-dominated phytoplankton depletedthe dissolved silicate in the river water and this led to acollapse of the populations, indicated by a decreased specificrate of photosynthesis (measured by the ¹⁴C method) and vigorousbacterial growth (measured by [³H]thymidine incorporation).Subsequently, the remaining phytoplankton diminished to verylow levels near the river mouth. In July and September, it seemedthat biological interactions within the plankton populationsor between plankton and benthos balance the population densitiesso that separate developmental stages, as in spring, were lessprominent. Estimates of the growth rates and loss rates of thephytoplankton were made. Phytoplankton exerted a substantialinfluence on the partitioning of nutrients (nitrogen, phosphorus,silicate) over water and suspended matter (as analysed by elementanalysis). It seems likely that only the reduction of phosphate,as planned under the Rhine Action Programme, and not that ofnitrogen, may restrict the peaks of plankton growth describedhere.     

“Green water” microalgae: the leading sector in world aquaculture

Freshwater fish culture is generally considered the largest sector in world aquaculture. Several of the leading species consume “green water” plankton. This plankton—mostly microalgae (phytoplankton) and also bacteria, protozoa and zooplankton—grows in man-made fertilized water impoundments. The quantity of “green water” microalgae consumed by fish and shrimp is estimated here at a quarter billion ton fresh weight a year, about three and a half times as much as the entire recognized aquaculture. This estimate is based on the quantities of the microalgae consumed and the efficiencies of their use for growth by the main species in aquaculture. The cost of producing “green water” microalgae by the aquaculturists—mostly in SE Asia—is low. The populations in “green water” are biologically managed by the cultured fish themselves. The fish with their different feeding habits help “manage” the composition of the plankton and the overall water quality as they grow. The aquaculturists further manage “green water” through simple means, including water exchange and fertilization. Cost is remunerated partially by the income from sales of the fish and partially by bio mitigation services that “green water” polyculture ponds provide the aquaculturists in treating farm and household waste. A comprehension of the scale and importance of the microalgae sector to world aquaculture should lead to more research to improve understanding of algal population dynamics, growth factors, and efficiency of food chains. The consequent improved control of the plankton’s interaction with fish and shrimp production in “green water” will undoubtedly contribute much to the expansion in production of seafood.     

鄱阳湖不同水文期浮游生物群落结构特征和影响因素及水质评价

为阐明鄱阳湖不同水文期浮游生物群落结构特征及其影响因素,研究于2017年8月(丰水期)和12月(枯水期)在鄱阳湖湖区典型水域设置5个采样点进行浮游生物采样调查。研究期间共鉴定浮游植物8门75属186种,丰水期与枯水期均以硅藻门和绿藻门为主。共鉴定浮游动物4类76种,丰水期与枯水期均以原生动物和轮虫为主。方差分析显示:浮游植物密度与生物量在不同水文期之间的差异均为极显著(P<0.01),浮游动物丰水期密度高于枯水期,但无显著差异(P>0.05),浮游动物生物量(P<0.05)在不同水文期差异显著。冗余分析(RDA)显示:丰水期透明度和浮游生物呈显著负相关关系,电导率和浮游生物呈显著正相关。透明度、电导率与营养盐是影响丰水期浮游生物群落结构的主要环境因素,枯水期水温和溶解氧是驱动鄱阳湖浮游生物群落生态分布的主要环境因素。基于Shannon-Wiener(H′)、Margalef(d)和Pielou(J)等生物多样性指数的水质评价结果表明:鄱阳湖研究区域水质状态处于寡污-中污之间。研究揭示了2个水文期对通江湖泊浮游生物的影响:季节变化不改变湖泊浮游生物的物种组成及优势种,但...     

Vertical distribution of zooplankton in the frontal zone of the Gulf Stream and Labrador Current

Zooplankton data collected during September 1995 in the NorthWest Atlantic at 4139'N, 4958'W (the location of the siteof the ‘Titanic’ wreck) were analysed. The regioninvestigated was characterized by a very sharp frontal zonebetween the Gulf Stream and the main stream of the LabradorCurrent. The total plankton biomass in the water column wasvery high. The macroplankton biomass values below the 600 mlayer were significantly higher as compared with the similarvalues measured before in other productive boreal regions ofthe Atlantic and Pacific oceans. A lot of dead mesoplanktonanimals occurred in the deep layers. The reason was that thecold-water mesoplankton advected by the Labrador Current diedoff intensively within the deep layers of the frontal zone andwere used as a food resource by the macroplankton carnivoresand scavengers that were very abundant there.     

Spatial changes in carbon and nitrogen stable isotopes of the plankton food web in a saline lake ecosystem

We investigated spatial changes in the isotope ratios of the plankton food web in Lake Chany, Siberia, Russia, especially at an estuarine transition zone of the lake. The δ¹³C values of particulate organic matter (POM) varied among the sampling sites, and increased with increasing pH of the lake water. This may reflect a shift by phytoplankton from using CO₂ to using bicarbonate for photosynthesis with increasing pH. The δ¹³C values of zooplankton community also changed at each site along with those of the POM. This was indicative of carbon isotope changes of plankton food webs between the stations along an environmental gradient.