Zooplankton Parameters Research Articles

Comparative study on physico-chemical parameters of water, zooplankton and macrophytes diversity under the exposure of farm-made prebiotics in a semi- intensive aqua-farming system

The present study intended to investigate the variation of the physico-chemical status, zooplankton and macrophytes diversity of three semi-intensive ponds (each having 0.40 acre of water area) under Khano village of Galsi-II Block of Purba Bardhaman district, West Bengal, India. One was marked with control (C: fed only with locally available fish feed) and two others ponds (P1 and P2: fed with farm-made prebiotics plus locally available fish feed) were considered as treatment. The ‘farm-made prebiotics’ (made of fish-meal, ground-nut oil cake, bar-yeast, jaggery: fermented) was applied directly into the pond water fortnightly at the rate of 15 kg per acre fortnightly up to three months. The ponds were reared with Catla (Catla catla): Rahu (Labeo rohita): mrigal (Cirrhinus mrigala) at the ratio of 3:4:3. The water samples were drawn on day15, day30, day45, day60, day75 and day 90 at six corners of each pond. The average value was considered while computing the results of physico-chemical parameters, viz., transparency, temperature, pH, electrical conductivity (EC), carbon dioxide (CO2), dissolved oxygen (DO), total hardness (TH), total alkalinity (TA), phosphate (PO43-), chloride (Cl-), ammoniacal-nitrogen (NH4+-N), nitrate-nitrogen (NO3--N), sodium (Na+) and potassium (K+ ). The variations in the diversity of zooplankton and macrophytes in the study area were also measured. A marked difference in the case of physico-chemical parameters as well as the zooplankton and macrophytes diversity were observed under prebiotic exposure which may finally help in better growth of the fish species under prebiotic exposure. Finally, the fish farmers will be highly benefited from the application of such farm-made prebiotics.

ЕКОЛОГО-ФАУНІСТИЧНІ ОСОБЛИВОСТІ УГРУПОВАНЬ ЗООПЛАНКТОНУ, ІХТІОФАУНИ У РІЧЦІ ІРПІНЬ

B a c k g r o u n d . Monitoring of ecosystems affected by military actions is an element of a comprehensive assessment of the state of the ecosystem in the post-war period. The results of this study are key for the post-war recovery of the war-affected region and assessment of the state and quality of water resources in the area for their further use, as well as for the assessment of the consequences of Russian armed aggression for local water ecosystems and the hydrological network of the region in general. In February-March 2022, the Kozarovytska dam was blown up, which caused flooding of the floodplain more than 20 km downstream. M e t h o d s . As a result of the flooding of agricultural lands, the waters of the Irpin River were polluted with products of human life (burial sites, cattle cemeteries, village toilets, places where livestock and birds are kept, fertilizers, decay products of plant remains) and flooded military equipment and ammunition. The purpose of this work is to study the zooplankton and ichthyofauna in the Irpin River and its tributaries the Moschunka and the Gorenka rivers. The study was conducted in the summer of 2023. A conical plankton net was used for zooplankton sampling. Quantitative parameters of zooplankton were determined according to Hensen's computational method in Bogorov's chamber using binoculars. R e s u l t s . Determination of the saprobiological state of the investigated water bodies was carried out according to the Pantle-Bucca method. Ichthyological samples were taken using a dip bag. During the experimental period, 10 species of zooplankton were found, which included rotifers, cladocera and copepods, and 3 species of fish. C o n c l u s I o n s . The obtained results indicate a significant decrease in the species richness of zooplankton in the studied reservoirs in comparison with last year's indicators, which can be explained by the consequences of anthropogenic load on the studied water ecosystems during the phase of active military operations within the Buchansky district.

The usage of a zooplankton digitization software to study plankton dynamics in freshwater fisheries

To better understand anthropogenically induced shifts of lake nutrient dynamics and subsequent consequences for fish and their zooplankton food sources, an increased spatial and temporal resolution of zooplankton monitoring data is needed. The Zooscan, an instrument mainly used in marine research, enables digitalization of zooplankton samples, and thereby substantially decreases the effort for zooplankton analysis. We present Zooscan analyses of zooplankton from the water column and in whitefish (Coregonus sp.) stomachs from Lake Starnberg (Germany, Central Europe), a large oligotrophic pre-alpine lake. Digitalized manual and automated analyses of important zooplankton parameters such as abundance, species composition, size development and reproductive measures of different taxa are given. The obtained results from automated and manual Zooscan analyses allow drawing conclusions on population dynamics, size developments and zooplankton food preferences by whitefish. In particular, we highlight the advantages of assessing reproductive cycles based on the documentation of egg-bearing individuals of e.g. cladocerans, which are of less importance in marine environments. While the results of automated analysis of stomach content were generally inaccurate, manual validation of digitized images was efficient for identification. Digitized images offer the possibility of fast access and convenient storage of zooplankton samples.

Rotifers in the Niger River, Niger: diversity and abundance in relation to environmental parameters

A first study of the rotifers of the Niger River in Niger is reported here. Two surveys took place under contrasting hydrological conditions: low-water level (16 April to 8 May 2018) and high-water level (1 to 15 February 2019). Zooplankton and physico-chemical parameters were sampled at eight stations spread over 520 km from Ayorou to Gaya. In total, 32 taxa were identified, including 26 at species level. During the low-water sampling, Polyarthra sp. (31%), Brachionus caudatus (23%), Synchaeta longipes (11%), Keratella tropica (7%) and Filinia longiseta (5%) were the most abundant, whereas Brachionus quadridentatu s (26%), Lecane hastata (25%), Keratella cochlearis (9%), Keratella lunaris (5%), Hexarthra sp. (3%) were dominant during the high-water sampling. The mean abundance of rotifers ranged between 14 × 103 ind. m−3 during the high-water sampling and 244 × 103 ind. m−3 during the low-water sampling. The highest diversity was observed in the three stations located upstream from the city of Niamey. The results reflect the difference in environmental parameters between the downstream and upstream Niamey stations. RDA analyses showed that the main environmental factors explaining the distribution of rotifers were dissolved oxygen, orthophosphate and nitrate concentrations.

How morphology shapes the parameter sensitivity of lake ecosystem models

A global sensitivity analysis of a lake ecosystem model (GOTM-FABM-PCLake) was undertaken to test the impacts of lake morphology on parameter sensitivity in three different lakes. The analysis was facilitated by the Parallel Sensitivity and Auto-Calibration tool (parsac) and included a screening step with the density-based Borgonovo's method followed by in-depth analysis with both Borgonovo's and the variance-based Sobol’ methods. The Borgonovo's method proved efficient in ranking the most influential parameters and its results were corroborated by the Sobol’ method. For total phosphorus and total nitrogen, parameters related to the benthic-pelagic coupling and phytoplankton, were particularly important for the shallower lakes, whereas the most important parameters for total nitrogen were related mainly to the benthic-pelagic coupling in the deepest lake. For chlorophyll a, phytoplankton and zooplankton parameters were most influential. We conclude that lake morphology shapes the parameter sensitivity of lake ecosystem models.

The importance of aquatic plants in maintaining zooplankton diversity and abundance: An experimental approach

The influence of different species and ecological forms of higher aquatic plants on the abundance, biomass and species diversity of zooplankton was investigated in experimental ecosystems (microcosms). It was shown that in the absence of fish and macroinvertebrate predators, the abundance and diversity of zooplankton in the plants beds increased. Not only phytophilous, littoral, and small planktonic crustaceans, but also some large obligate planktonic crustaceans, reached a high abundance among the plants. Plants belonging to different ecological groups stimulated an increase in the abundance of different groups of zooplankton. In the beds of submerged plants, the number of Cladocera increased to a greater extent than Copepoda or Rotifera. The abundance of Copepoda, both Cyclopoida and Calanoida, grew in the beds of helophytes. The relative number of predators in the community increased among the plants. The species structure and quantitative parameters of zooplankton had their own characteristics in monospecies and mixed phytocenoses of the same plant species. The index of species diversity of zooplankton acquired the highest values in the mixed phytocenosis. Higher aquatic plants increase spatial heterogeneity, which stimulates the development of facultative planktonic and benthic species. The formation of phytogenic detritus and the lifetime release of organic substances by plants into the water causes the development of bacteria and protozoa, which expands the quality and size range of food organisms for zooplankton. Therefore, zooplankton becomes more diverse in terms of the set of trophic groups.

El Zooplancton de dos lagos someros del sur de la Formación Meauco (ProvincIa de la Pampa, Argentina)

The Meauco Formation, a dune region of the central Pampa province, has numerous shallow lakes. Although there is hydrological information about them, it is very scarce about their limnological characteristics. The objectives are to know the physical-chemical and zooplankton parameters of two nearby shallow lakes, with and without fishes: Santa Isabel I (SI I) and Santa Isabel II (I II) respectively, and determine the influence of zooplankton on phytoplankton biomass and transparency. It was sampled during 2018 and 2019. In both the mean salinity were less than 1g.L-1 and the Secchi disk depth was around 0.45m. The chlorophyll concentrations varied between 9.32 and 11.63 mg.m-3. Seven cladocerans, 4 copepods and 20 rotifers were recorded. Most of the taxa were shared by both lakes, however, 20 rotifers were recorded in SI I and 13 in SI II. The total zooplankton density did not differ, but SI I had greater abundance of rotifers (69% of total) and SI II of crustaceans (72%). The presence of fish influences the zooplankton composition but its small size, even in the absence of fish, makes it have little influence on the phytoplankton; therefore, no differences were found in the transparency and phytoplankton biomass of both lakes.

A lake-wide approach for large lake zooplankton monitoring: Results from the 2006–2016 Lake Superior Cooperative Science and Monitoring Initiative surveys

Whole-lake surveys of Lake Superior were completed during late summer in 2006, 2011, and 2016 to assess lower food web conditions under the Cooperative Science and Monitoring Initiative (CSMI). These surveys used a spatially stratified probability approach based on depth to assess food web conditions within different depth zones. We evaluated differences in crustacean zooplankton biomass, rotifer density, and the community structure of both groups in nearshore (<30 m), midshore (30–100 m), and offshore (>100 m) depth zones and investigated changes in these parameters within zones over time. Although nearshore crustacean biomasses and rotifer densities were highly variable, the depth zones differed from each other based on these parameters and should be considered separately. Crustacean biomass, community structure, and vertical position were consistent over time across depth zones. The differences that did occur were within the range of known annual variability. Total rotifer densities were lower in 2016 than in 2006 in all depth zones, but the genera that contributed to the lower values were not the same across zones. Further studies are needed to know whether these differences reflect annual variability or long-term trends. Finally, we show how the depth zones used in this study can facilitate comparisons between monitoring programs. This is important because most zooplankton studies are limited to certain depth zones and changes in zooplankton parameters may not occur uniformly across zones. The high variability in nearshore zooplankton parameters suggests that additional research may be needed to effectively track changes there.

Zooplankton indicator-based assessment in relation to site location and abiotic factors: a case study from the Gulf of Riga.

There are a number of zooplankton parameters proposed as indicators to evaluate environmental status of marine ecosystems. Mean size and total stock (MSTS) is the only zooplankton-based and HELCOM (Baltic Marine Environment Protection Commission - Helsinki Commission)-approved core indicator. MSTS was developed to evaluate the environmental status of the Baltic Sea based on total biomass (or abundance) and mean body weight of mesozooplankton. This indicator reflects status of the food web and zooplankton biodiversity. Both are qualitative descriptors for determining good environmental status (GES) as defined by the EU Marine Strategy Framework Directive 2008/56/EC. However, the existing indicator concept is applicable to the extent that it characterizes off-shore pelagic habitats, while use of MSTS for coastal habitats remains challenging. In this case study, we aimed to assess and discuss performance of MSTS applied to mesozooplankton data from the shallow Gulf of Riga. Both off-shore and coastal communities were included in the study. MSTS responses to variable environmental factors (temperature, salinity and riverine runoff) were analysed. Temporal variations in temperature revealed response in mean size, whereas salinity covaried with total stock (both - biomass and abundance). However, spatial variations of MSTS parameters stayed unexplained. The results demonstrate difficulties with and provide possible solutions for MSTS-based assessment, with a particular emphasis on coastal waters. The use of mesozooplankton abundance as a determinant parameter for assessment of coastal waters and substitution of the corresponding 99% confidence interval of the mean as an assessment value instead of the mean have been considered.

Is the zooplankton of mesosaline lakes in protected areas in the semiarid Pampa of Argentina different from those in lakes with high anthropic influence?

Most of the mesosaline lakes in the semiarid central Pampas have a high anthropic influence. The objective was to determine the limnological and zooplankton parameters of a mesosaline lake with little human impact, the West Lake of the Parque Luro Reserve, and compare it with previously studied aquatic ecosystems. Monthly samples were taken (2014–2015). The mean depth and salinity were 0.66 m and 29.33 g/L, respectively. The transparency was high and favored the growth of the macrophyte Ruppia cirrhosa. Zooplankton diversity was low, with autochthonous halophilic crustaceans (Daphnia menucoensis and Boeckella poopoensis). Zooplankton density was 20 to 100 times lower than that of other pampean lakes, probably due to the presence of the macrophyte, which distinguishes this lake from others in the region.

ZOOPLANKTON OF LAKE ONEGO IN ITS CENTRAL PART AND BOLSHOE ONEGO BAY IN YEARS WITH DIFFERENT TEMPERATURE COMDITIONS

The pelagic plankton system of Lake Onego, in its central part and Bolshoe Onego Bay, has a high structural and dynamic stability. The purpose of this study was to assess the state of zooplankton in Lake Onego and its seasonal variation in years with different temperature conditions based on data for 2015–2017. The main zooplankton parameters, its composition, structure, and features of the annual cycle have been preserved over this period, but an elevated spatial-temporal variation was observed, associated with the different thermal regimes in these years. In July 2016, zooplankton development shifted to earlier dates and reached extremely high parameters, atypical of this period (abundance of 6,200 ind./m3 and biomass of 0.21 g/m3). The first decade of August 2015 was noted for low amounts of zooplankton (abundance of 1,200 ind./m3 and biomass of 0.03 g/m3), whereas the same period in 2017 was characterized by its elevated amounts (abundance of 7,500 ind./m3 and biomass of 0.17 g/m3). Zooplankton abundance and biomass in June and October corresponded to their long-term averages, taking into account interannual fluctuations. The detection of extremely deviating minimum and maximum zooplankton abundances may indicate that the lake’s plankton system is beginning to lose balance in the conditions of temperature differences among years.

Water quality of Tehri dam reservoir and contributing rivers in the Himalayan region, India

In nature, the main resources for the availability of water are ponds, lakes, tanks, rivers, and shallow water basins. The water quality available in these water bodies is subjected for continuous change which is due to eutrophication of these water bodies. The water quality often becomes a problem to sustain it. The present investigation was undertaken to study water quality parameters of the Tehri dam reservoir and contributing rivers with an objective to indicate changes in the quality of waters in the contributing rivers and in the reservoir after impoundment and to suggest suitable measures to protect reservoir water quality. Temperature of Bhagirathi river water ranged between 16 and 28 °C while Tehri reservoir water showed it in between 29.5 and 32 °C. DO levels in the reservoir varied between 8.4 and 9.6 mg/L which are similar to river water (8.4–9.4 mg/L). Thus, there is no effect of impounding of river water on the DO which is sufficient for sustaining fisheries and other aquatic lives. Tehri dam reservoir water shows lower turbidity as compared to river water. River Bhagirathi had unique features of the presence of certain radioactive elements and specific groups of coliphages that are likely to maintain self-preservation of the water. DO, COD, BOD, heavy metals, radioactive elements, etc., were within permissible limits, as per categories ‘B‘ and ‘C’, specified by CPCB for outdoor bathing and drinking water source with conventional treatment. However, such waters also fulfill categories ‘D’ and ‘E’, designated for propagating wildlife/fish and irrigation/cooling purpose, respectively. Biological parameters of phytoplankton and zooplankton were analyzed to determine the effect of impounding on the flora and fauna of reservoir, wherein plankton diversities in river and reservoir samples were comparable. The Palmer’s Pollution Index ranged between 3 and 5 for phytoplankton while Shannon–Wiener Diversity Index varied from 2 to 2.86 for zooplankton, indicating low to moderate productive waters.

A Comparative Study of the Far Eastern Seas and the Northern Pacific Ocean Based on Integral Parameters of Net Zooplankton in the Epipelagic Layer

Integral parameters of zooplankton community, including species diversity and its components were compared between the Chukchi Sea, Bering Sea, Sea of Okhotsk, Sea of Japan, and adjacent Pacific waters based on the data obtained by standard Juday net with a mouth area of 0.1 m2 during the large-scale surveys conducted by the Pacific Fisheries Research Center (TINRO Center) in 1984–2013. These parameters were calculated for the total surveyed area of approximately 7.0 million km2 and separately for each of the considered water bodies. In Pacific waters, species richness is higher than that in all the seas, while the concentration of individuals (expressed in terms of abundance, ind./m3) and evenness of their distribution over species were lower. The only sea with a larger mean size of organisms compared to the ocean is the Bering Sea. A lower species diversity than in the ocean has been recorded only from the Chukchi Sea; a lower density (in terms of biomass, g/m3) was determined only from the Sea of Japan. Among the four seas, the Chukchi Sea ranks first in terms of biomass and abundance of zooplankton, second in species evenness, third in the mean size of individuals, and last in species richness and diversity. The Bering Sea ranks first in terms of mean size of plankton organisms, second in species richness, diversity, and biomass, third in abundance, and last in species evenness. The Sea of Okhotsk ranks second in terms of mean size of individuals, last in their abundance, and third in the other parameters. The Sea of Japan ranks first in terms of species richness, evenness, and diversity, second in abundance, and last in mean size of zooplankton organisms, and, therefore, their biomass. The biomass of zooplankton, in accordance with the concentration of nutrients, increases in the southto-north direction (while its absolute abundance depends largely on the size of the body of water). The mean size of organisms increases in the same direction; the evenness of their distribution over species increases in the reverse direction (with the exception of both parameters for the Chukchi Sea). The rank of a water body for its biodiversity coincides with the species richness rank. The latter increases from north to south (except for the Okhotsk Sea), but greatly depends on the surveyed area and, even more, on the surveyed volume of water. A study of the literature data found some unexpected statistically significant relationships of the integral parameters of zooplankton with those of pelagic and bottom macrofauna, as well as with the parameters of zooplankton production, on the size of the considered bodies of water. The causes and the biological meanings of most of these relationships still do not have any rational interpretation. Their testing at other spatial scales will be continued in future works.

Environmental and zooplankton parameter changes during the drying of a saline shallow temporary lake in central Argentina

Central Argentina has numerous saline lakes sustained by groundwater sources and rainfall. These lakes are temporary and experience significant changes in water level and salinity, depending on wet and dry climate cycles. This study aims to investigate the scarcely known dynamics of environmental and zooplankton parameters during the drying phase of one of these lakes. Monthly samples were taken from December 2 012&lt;br /&gt;to July 2 013 in the Ojo de Agua Uriburu lake, previous to its drying. At the beginning of the study, the lake’s depth was 0.7 m and its salinity was 16.65 g/L, later, in July, its depth decreased to 0.06 m and its salinity increased to 92.9 g/L. Zooplankton species richness was low (three crustaceans and three rotifers), with &lt;em&gt;Boeckella poopoensis&lt;/em&gt; and &lt;em&gt;Moina eugeniae&lt;/em&gt; dominating in the system. Maximum density and biomass were attained&lt;br /&gt;by the two dominant species in April (318.5 ind/L and 3 029.1 g /L dry weight; and 242.4 ind/L and 1 530.4 g/L dry weight, for &lt;em&gt;B. poopoensis&lt;/em&gt; and &lt;em&gt;M. eugeniae&lt;/em&gt;, respectively), and no correlation was found between these parameters and salinity. Maximum average body lengths for both species were observed in the last months of sampling (&lt;em&gt;M. eugeniae&lt;/em&gt;: 1 020 84.2 m and&lt;em&gt; B. poopoensis&lt;/em&gt;: 1 348.8 89.0 m). At this point of the study, neither juvenile nor larval stages were found. The increase in average body size is, arguably, the result of increased salinity in the system through a negative&lt;br /&gt;effect on reproduction. Because this lake reached hypersalinity, its ecological dynamics are unique among those of other temporary, saline lakes that dried in central Argentina. Similar studies on other temporary ecosystems are needed to increase the information on these little known ecological aspects.

Comparative study of the Far-Eastern Seas and the North Pacific by integral parameters of net zooplankton in the epipelagic layer

Species diversity and other integral parameters of zooplankton community in the Japan, Okhotsk, Bering, Chukchi seas and adjacent Pacific waters (total area close to 7.0 . 10 6 km 2 ) are compared on the data obtained in the large-scale surveys conducted by Pacific Fish. Res. Center (TINRO) in 1984-2013. Standard Juday net with mesh size 0.186 mm and mouth area 0.1 m 2 was used for sampling. Among four seas, the Chukchi Sea takes the 1 st place by abundance (ind./m 3 ) and biomass (mg/m 3 ) of zooplankton, 2 nd by species evenness, 3 rd by mean size of organisms, and the last by species richness and diversity. The Bering Sea is the 1 st by mean size of animals, 2 nd by species richness, diversity and biomass, 3 rd by abundance, and the last by species evenness. The Okhotsk Sea takes the 2 nd place by mean size of zooplankton, the last by its abundance, and the 3 rd by other parameters. The Japan Sea is the 1 st by species richness, evenness and diversity, 2 nd by abundance, and the last by mean size of zooplankton and therefore by its biomass. Zooplankton in the Pacific waters has the lowest abundance, but its biomass is higher there in comparison with the Japan Sea. Species richness is the highest in the Pacific, but species diversity is higher there than in the Chukchi Sea and species evenness is the lowest. Mean size of zooplankton organisms in the Pacific is rather large but smaller than in the Bering Sea. In general, zooplankton abundance increases northward in accordance with nutrients supply, as well as the mean size of animals (with exclusion of the Chukchi Sea), but uniformity of the species abundance has opposite tendency (except the Chukchi Sea again). The rank in biodiversity coincides with the rank in species richness. The latter decreases from south to north (with exclusion of the Okhotsk Sea), but depends strongly on size of the surveyed area and surveyed volume of water. Some unexpected statistically significant relationships are found between the integral parameters of zooplankton and these parameters for pelagic and bottom macrofauna which have not yet any rational interpretation.

Calibrating a global three-dimensional biogeochemical ocean model (MOPS-1.0)

Abstract. Global biogeochemical ocean models contain a variety of different biogeochemical components and often much simplified representations of complex dynamical interactions, which are described by many ( ≈ 10 to ≈ 100) parameters. The values of many of these parameters are empirically difficult to constrain, due to the fact that in the models they represent processes for a range of different groups of organisms at the same time, while even for single species parameter values are often difficult to determine in situ. Therefore, these models are subject to a high level of parametric uncertainty. This may be of consequence for their skill with respect to accurately describing the relevant features of the present ocean, as well as their sensitivity to possible environmental changes. We here present a framework for the calibration of global biogeochemical ocean models on short and long timescales. The framework combines an offline approach for transport of biogeochemical tracers with an estimation of distribution algorithm (Covariance Matrix Adaption Evolution Strategy, CMA-ES). We explore the performance and capability of this framework by five different optimizations of six biogeochemical parameters of a global biogeochemical model, simulated over 3000 years. First, a twin experiment explores the feasibility of this approach. Four optimizations against a climatology of observations of annual mean dissolved nutrients and oxygen determine the extent to which different setups of the optimization influence model fit and parameter estimates. Because the misfit function applied focuses on the large-scale distribution of inorganic biogeochemical tracers, parameters that act on large spatial and temporal scales are determined earliest, and with the least spread. Parameters more closely tied to surface biology, which act on shorter timescales, are more difficult to determine. In particular, the search for optimum zooplankton parameters can benefit from a sound knowledge of maximum and minimum parameter values, leading to a more efficient optimization. It is encouraging that, although the misfit function does not contain any direct information about biogeochemical turnover, the optimized models nevertheless provide a better fit to observed global biogeochemical fluxes.

Comparison of acoustical and optical zooplankton measurements using an acoustic scattering model: A case study from the Arctic frontal zone

Abstract High-frequency acoustic measurements supplemented by a modern optical method, Laser Optical Plankton Counter (LOPC), allowed us to perform a comparative analysis through the application of a mathematical model. We have studied the correspondence between measured and modelled echoes from zooplankton aggregations consisted mainly of two Calanus species. Data were collected from the upper 50 m water layer within the hydrographical frontal zone on the West Spitsbergen Shelf. The application of a “high-pass” model of sound scattering by fluid-like particles to the distribution of zooplankton sizes measured by LOPC resulted mostly in very good agreement between the measured (420 kHz BioSonics) and modelled values, except for cases with very low zooplankton abundance or with occurrence of stronger scatterers (e.g. macrozooplankton, fish). An acoustic model validated for the elastic parameters of zooplankton confirmed that particles smaller than 1mmin diameter, although highly abundant, did not contribute significantly to the sound scattering process at a frequency of 420 kHz. The implementation of diverse complementary methods has great potential to obtain high spatial and temporal resolution in zooplankton distribution studies; however, their compatibility has to be tested first.

Which environmental scales and factors matter for mesozooplankton communities in a shallow brackish water ecosystem?

Aquatic invertebrate communities are influenced by interactions between the abiotic and biotic environment at multiple spatial and temporal scales. Studies of mesozooplankton community patterns in relation to spatial and temporal scales are rare. In this study, we examined scale-specific variability of mesozooplankton in the shallow coastal Baltic Sea and related this variability to key environmental proxies. Seasonality defined the majority of variability in taxonomic composition and abundance patterns, as well as in aggregated parameters of zooplankton. However, these properties also varied spatially at a large, 100-km scale. The variability in all properties except taxonomic composition was negligible at the smaller spatial scale. Taxonomic richness increased until moderate levels of total abundance, whereas peak blooms were always characterized by higher dark diversity. Shannon diversity was unrelated to total abundance. Observed spatio-temporal patterns were strongly related to abiotic forcing and uncoupled from phytoplankton standing stock and primary production. Results show the importance of seasonality over spatial variability and abiotic factors over phytoplankton variability for sub-boreal brackish coastal mesozooplankton at the spatial scales studied. Information loss from spatial generalization can be larger for taxonomic occurrences and rare species than for species abundances and aggregated community parameters such as total abundance or taxonomic richness.

Response of the Baltic and North Seas to river runoff from the Baltic watershed – Physical and biological changes

Selected Baltic Sea watershed River Runoff (BSRR) events during 1970–2000 were used as predictor in Generalised Linear Mixed Models (GLIMMIX) for evidence of simultaneous changes/chain of events (including possible time lags) in some chemical, physical and biological variables in the Baltic and North Sea ecosystems. Our aim was to explore for climatic-based explanation for ecological regime shifts that were documented semi-simultaneously in both ecosystems. Certain similarities were identified in the North Sea and the Baltic Sea salinity, oxygen concentration, temperature and phyto- and zooplankton parameters. These findings suggest that BSRR events which originate in the Baltic Sea catchment area modify and contribute to large scale ecosystem changes not only in the Baltic Sea, but also in the adjacent parts of the North Sea. However, the Baltic Sea inter-annual and inter-decadal variabilities of physical and biological parameters are driven by direct atmospheric forcing, typically with a relatively short lag. In contrast, such changes in the North Sea are influenced by both local and direct atmospheric forcing, typically with a longer lag than in the Baltic, and a more regional, indirect forcing from changes in the North Atlantic. We suggest that this interactive system partially is behind large scale ecosystem regime shifts found in both Seas. During our study period two such shifts have been identified independently from us in a study earlier in the Southern and Central Baltic in 1980s and 1990s and a later one in 2001/2002 in the North Sea. As a post hoc test we compared the 0+ year class strength of the North Sea herring with BSRR intensity, and found evidence for higher herring production in high BSRR periods, which further corroborates the idea of a remote effect from the large watershed area of the Baltic. Regime shifts as well as their semi-synchronous appearance in two neighbouring sea areas could be identified. GLIMMIX models provide opportunities for determining and understanding the mechanisms behind marine ecosystem long-term and large-scale changes. Many studies have shown the importance of climatic factors (identified by the air pressure index, North Atlantic Oscillation) to the physical and biological changes over the North Atlantic. Our study enlarges the areal and temporal scope of these observations, and provides further support and explanation for climate as the pacemaker for marine ecological changes.

Distribution of plankton and fish in Lake Sevan (Armenia) during the process of mass growth of cladocerans

This study presents data on the quantitative parameters of bacterioplankton, zooplankton, and fish at the current stage of development of Lake Sevan. This stage is characterized by an increase in water level, a significant reduction in fish stock, and the maximum biomass of zooplankton (due to the massive development of cladocerans) observed during the entire period of lake investigations.