Zooplankton Concentrations Research Articles

Spawning ecology of the European anchovy (Engraulis encrasicolus) in the Strait of Sicily: Linking variations of zooplankton prey, fish density, growth, and reproduction in an upwelling system

A 12-year time series (2005–2016) was examined to explore relationships between European anchovy density, growth, reproduction and habitat dynamics in an upwelling system. Specifically, data used for a daily egg production method were combined with oceanographic data, prey availability, as well as acoustic surveys of the anchovy stock in the Strait of Sicily, in the Central Mediterranean Sea. Variables typically used for evaluating habitat dynamics (i.e. water temperature, chlorophyll-a, zooplankton concentration, kinetic energy, mixed layer depth and upwelling index) indicated strong upwelling events during the summer, when anchovy spawns. A linear ‘principal component’ combination of environmental traits, associated with summer upwelling, was identified by step-wise regression as a driver for growth (length at the end of the first year; L1), reproductive investment (gonad-somatic index; GSI), as well as egg production (daily specific fecundity; DSF). These relationships are consistent with direct energy flow from the environment to both somatic growth and reproductive output, indicating an income breeding strategy by anchovy (i.e. surplus energy acquired during the summer breeding season is used directly for reproductive growth). Step-wise regression also identified three additional relationships: (1) a density-dependent mechanism reducing growth (L1) and fecundity (DSF) at higher fish densities; (2) higher fish condition (Kn) positively affecting growth (L1); (3) higher prey availability (mesozooplankton concentration) positively affecting GSI. This time series and approach are promising for exploring the abiotic and biotic mechanisms setting year class strength in advance of recruitment to the fishery.

Detecting Mesopelagic Organisms Using Biogeochemical-Argo Floats.

During the North Atlantic Aerosols and Marine Ecosystems Study in the western North Atlantic, float‐based profiles of fluorescent dissolved organic matter and backscattering exhibited distinct spike layers at ∼ 300 m. The locations of the spikes were at depths similar or shallower to where a ship‐based scientific echo sounder identified layers of acoustic backscatter, an Underwater Vision Profiler detected elevated concentration of zooplankton, and mesopelagic fish were sampled by a mesopelagic net tow. The collocation of spike layers in bio‐optical properties with mesopelagic organisms suggests that some can be detected with float‐based bio‐optical sensors. This opens the door to the investigation of such aggregations/layers in observations collected by the global biogeochemical‐Argo array allowing the detection of mesopelagic organisms in remote locations of the open ocean under‐sampled by traditional methods.

A Global Model for Methylmercury Formation and Uptake at the Base of Marine Food Webs

AbstractMonomethylmercury (CH3Hg) is the only form of mercury (Hg) known to biomagnify in food webs. Here we investigate factors driving methylated mercury [MeHg = CH3Hg + (CH3)2Hg)] production and degradation across the global ocean and uptake and trophic transfer at the base of marine food webs. We develop a new global 3‐D simulation of MeHg in seawater and phyto/zooplankton within the Massachusetts Institute of Technology general circulation model. We find that high modeled MeHg concentrations in polar regions are driven by reduced demethylation due to lower solar radiation and colder temperatures. In the eastern tropical subsurface waters of the Atlantic and Pacific Oceans, the model results suggest that high MeHg concentrations are associated with enhanced microbial activity and atmospheric inputs of inorganic Hg. Global budget analysis indicates that upward advection/diffusion from subsurface ocean provides 17% of MeHg in the surface ocean. Modeled open ocean phytoplankton concentrations are relatively uniform because lowest modeled seawater MeHg concentrations occur in oligotrophic regions with the smallest size classes of phytoplankton, with relatively high uptake of MeHg and vice versa. Diatoms and synechococcus are the two most important phytoplankton categories for transferring MeHg from seawater to herbivorous zooplankton, contributing 35% and 25%, respectively. Modeled ratios of MeHg concentrations between herbivorous zooplankton and phytoplankton are 0.74–0.78 for picoplankton (i.e., no biomagnification) and 2.6–4.5 for eukaryotic phytoplankton. The spatial distribution of the trophic magnification factor is largely determined by the zooplankton concentrations. Changing ocean biogeochemistry resulting from climate change is expected to have a significant impact on marine MeHg formation and bioaccumulation.

NUMERICAL SIMULATION FOR SEASONAL AND INTER-ANNUAL CHANGE OF DISSOLVED OXYGEN IN LAKE BIWA, JAPAN

The dynamics of dissolved oxygen in lake is a fundamental issue of comprehending the water environmental habitats of aquatic organisms. In recent years, the decrease in dissolved oxygen has been observed at the bottom of the northern part of Lake Biwa, Japan. In recent years, eutrophication and global warming caused the decrease in the dissolved oxygen in the deep layer. Under these circumstances, in order to preserve the ecosystem of Lake Biwa and to provide water resources, the environmental changes in Lake Biwa should be accurately grasped. In our present study, a water quality model considering the flow field from hydrodynamic model was developed in order to grasp the concentration of phytoplankton, zooplankton, nitrogen, phosphorus, dissolved oxygen and chemical oxygen demand in Lake Biwa. Numerical simulation was carried out for 3 years from 2007 to 2009. Comparisons of the simulations with the observations showed that the seasonal and interannual change of dissolved oxygen was well reproduced. The dissolved oxygen decreased during decomposingthe organic matter by bacteria in the bottom layer with little oxygen supply from the atmosphere and the photosynthesis from the phytoplankton under the thermocline from spring to autumn. The simulation confirmed that in each year, the dissolved oxygen was supplied in all layers by the overturning in winter.

Mycosporine-Like Amino Acids (MAAs) in Zooplankton.

Organisms have different adaptations to avoid damage from ultraviolet radiation and one such adaptation is the accumulation of mycosporine-like amino acids (MAAs). These compounds are common in aquatic taxa but a comprehensive review is lacking on their distribution and function in zooplankton. This paper shows that zooplankton MAA concentrations range from non-detectable to ~13 µg mgDW−1. Copepods, rotifers, and krill display a large range of concentrations, whereas cladocerans generally do not contain MAAs. The proposed mechanisms to gain MAAs are via ingestion of MAA-rich food or via symbiotic bacteria providing zooplankton with MAAs. Exposure to UV-radiation increases the concentrations in zooplankton both via increasing MAA concentrations in the phytoplankton food and due to active accumulation. Concentrations are generally low during winter and higher in summer and females seem to deposit MAAs in their eggs. The concentrations of MAAs in zooplankton tend to increase with altitude but only up to a certain altitude suggesting some limitation for the uptake. Shallow and UV-transparent systems tend to have copepods with higher concentrations of MAAs but this has only been shown in a few species. A high MAA concentration has also been shown to lead to lower UV-induced mortality and an overall increased fitness. While there is a lot of information on MAAs in zooplankton we still lack understanding of the potential costs and constraints for accumulation. There is also scarce information in some taxa such as rotifers as well as from systems in tropical, sub(polar) areas as well as in marine systems in general.

Mercury bioaccumulation in zooplankton and its relationship with eutrophication in the waters in the karst region of Guizhou Province, Southwest China.

Zooplankton play an important role in the transfer of mercury (Hg) from the lower to upper trophic positions in the food chain. In this study, total mercury (THg) and methylmercury (MeHg) levels were measured in three size fractions of zooplankton collected from three reservoirs (Hongfeng, Baihua, and Aha Reservoir) and one wetland in karst areas to understand mercury accumulation in zooplankton from alkaline environments. The results showed that the alkaline waters had lower zooplankton MeHg levels (0.1 to 66.8ngg-1) than most of the acidic waters reported. However, the zooplankton THg levels (6.3 to 494.9ngg-1) were comparable. The macro-zooplankton (> 500μm) had significantly higher THg and MeHg levels than meso-zooplankton (116 to 500μm) in the three reservoirs at all seasons, which showed biomagnification of mercury in the food chain. The correlation between Hg in water and zooplankton and Hg in zooplankton of different sizes indicated that THg bioaccumulation in zooplankton was related to the THg levels in water; however, MeHg bioaccumulation in zooplankton was controlled by many other factors, such as their feeding and living habits. In the three reservoirs, the THg and MeHg concentrations in zooplankton decreased with increasing eutrophication. However, compared with the three reservoirs, Caohai Wetland, with large amounts of aquatic plants, had a much lower trophic level and higher MeHg content in water but much lower zooplankton MeHg levels and bioaccumulation factors (BAFs). The large amounts of plant residue might dilute mercury in the food chain, revealing that high primary production could result in lower Hg bioaccumulation, rather than only being influenced by nutrient levels.

Changing with the tides: fine-scale larval fish prey availability and predation pressure near a tidally modulated river plume

Tidally controlled river plumes form distinct frontal boundaries that can alter the spatial distributions of larval fishes and their planktonic prey and predators. Variable in nature, they may expose larval fishes to different trophic environments over small spatio-temporal scales, with unknown consequences for survival and recruitment. In the northern California Current, the Columbia River Plume is strongly influenced by twice-daily freshwater injections that create a highly dynamic coastal environment. Using the In situ Ichthyoplankton Imaging System, we examined changes in the fine-scale horizontal and vertical distributions of larval fishes, their prey, and their predators over space and time (ebb/flood tide). In total, 6095 fish larvae and ~1.5 million prey/predator zooplankton were imaged and measured. Plume regions provided substantially higher concentrations of prey and enhanced spatial overlap between larval fishes and their prey relative to oceanic waters. The functionality of river plumes as a refuge from predators was less clear. Predator concentrations were also higher in plume regions, but overlap with larval fishes was taxon-specific and varied with the tide. Notably, regions of high zooplankton concentrations did not necessarily confer high spatial overlap on small scales (meters vertical, kms horizontal) relevant to trophic interactions. Surface salinity and chlorophyll a were the most important factors influencing the spatial overlap of zooplankton with larval fishes. In the vicinity of river plumes, larval fishes experience a diversity of unique prey and predator fields over short spatio-temporal scales, which likely contribute to variable growth and mortality patterns at much finer scales than previously thought.

Reducing dietary protein concentrations and replacing fish meal with porcine meat and bone meal do not affect growth or feed conversion of pond‐raised fingerling channel catfish, Ictalurus punctatus

AbstractThis study evaluated dietary protein concentrations and replacing fish meal with porcine meat and bone meal (PMB) for pond‐raised fingerling channel catfish, Ictalurus punctatus. Three diets were formulated to have 28, 32, or 35% protein using soybean meal, cottonseed meal, and fish meal as the main protein sources, respectively. A fourth diet contained 32% protein with fish meal being replaced with PMB. Analyzed protein concentrations were 29.7, 31.9, 34.4, and 31.1% on 90% dry matter basis, respectively. Small fingerlings (average initial weight: 2.0 g/fish) were stocked in 20 earthen ponds (0.04 ha) at 172,970 fish/ha and were fed once daily to apparent satiation for 98 days. There were no significant differences in total diet fed, gross yield, final weight, feed conversion ratio, survival, or condition factor among diets. There were also no significant differences in ammonia‐N, nitrite‐N, chlorophyll a, or desirable zooplankton concentrations in pond water of fish receiving different diets. Results show that a diet containing about 30% protein can support optimum growth of pond‐raised channel catfish fingerlings of 2 g and larger in fertilized ponds fed once daily to apparent satiation. PMB can completely replace fish meal in a 32% protein diet. Economic analysis suggests considerable cost savings by replacing fish meal with PMB and reducing protein concentrations in channel catfish fingerling diets.

Environmental effects on the bioaccumulation of PAHs in marine zooplankton in Gaoping coastal waters, Taiwan: Concentration, distribution, profile, and sources

Polycyclic aromatic hydrocarbons (PAHs) are toxic and ubiquitous in the environment and pose great risks. Bioaccumulation by plankton is the outset for PAHs entering marine food web. The long-term driving environmental factors for bioaccumulation of PAHs in zooplankton have not been well investigated. In this study, high variation of PAH concentrations in zooplankton (5 to 5440 ng g−1 dry weight) was found, with the highest PAH levels near the transect Kaohsiung Harbor. Precipitation significantly enhances the PAH concentration in zooplankton and affects the PAH distribution in the water column, indicating PAH input from terrestrial runoff. The sources of PAHs in the coastal waters are a mixture of petroleum and combustion. Biomass dilution dominates bioaccumulation of PAHs in zooplankton, especially for the dominant species, copepods. This study provides the first information on PAH bioaccumulation in zooplankton to understand PAH transport in the plankton food web in subtropical coastal waters.

Terrestrial organic matter increases zooplankton methylmercury accumulation in a brown-water boreal lake

Increases in terrestrial organic matter (tOM) transport from catchments to boreal lakes can affect methylmercury (MeHg) accumulation in aquatic biota both directly by increasing concentrations of aqueous MeHg, and indirectly through effects on MeHg bioavailability and on energy pathways in the lower food web. We carried out a detailed seasonal study of water chemistry, zooplankton diet, and MeHg accumulation in zooplankton in two lakes with contrasting tOM concentrations. Between-lake differences explained 51% of the variability in our water chemistry data, with no observed effect of season or sampling depth, contrary to our expectations. Higher tOM was correlated with higher aqueous Hg concentrations, lower areal pelagic primary productivity, and an increased contribution of terrestrial particles to pelagic particulate organic matter. Based on dietary marker analysis (δ13C, δ15N, and fatty acid [FA] composition), zooplankton diet was strongly linked to feeding mechanism, with dietary reliance on phytoplankton highest in the selective-feeding calanoid copepods, and lowest in filter feeding cladocerans. Zooplankton dietary reliance on phytoplankton and their concentrations of high-quality lipids, including polyunsaturated fatty acids, were higher in the clear-water lake than in the brown-water lake, where bacterial and terrestrial food sources were more prevalent. MeHg was highest in zooplankton from the brown-water lake, with highest concentrations in the 200–500 μm zooplankton size fraction for both lakes. Contrary to our expectations, there was no effect of season on zooplankton dietary markers or MeHg. Our results suggest that, overall, higher tOM results in higher MeHg concentrations in water and zooplankton, and reduces zooplankton dietary reliance on phytoplankton. Increased tOM thus leads to a decrease in the nutritional quality of zooplankton (i.e. higher MeHg concentrations, and lower concentrations of essential fatty acids), which may cascade up the food web with negative implications for higher trophic levels.

Nutrients mediate the effects of temperature on methylmercury concentrations in freshwater zooplankton

Methylmercury (MeHg) bioaccumulation in freshwater aquatic systems is impacted by anthropogenic stressors, including climate change and nutrient enrichment. The goal of this study was to determine how warmer water temperatures and excess nutrients would alter zooplankton communities and phytoplankton concentrations, and whether those changes would in turn increase or decrease MeHg concentrations in freshwater zooplankton. To test this, we employed a 2 × 2 factorial experimental design with nutrient and temperature treatments. Mesocosms were filled with ambient water and plankton from Cottage Grove Reservoir, Oregon, U.S.A., a waterbody that has experienced decades of elevated MeHg concentrations and corresponding fish consumption advisories due to run-off from Black Butte Mine tailings, located within the watershed. Treatment combinations of warmer temperature (increased by 0.7 °C), nutrient addition (a single pulse of 10× ambient concentrations of nitrogen and phosphorous), control, and a combination of temperature and nutrients were applied to mesocosms. The individual treatments altered phytoplankton densities and community structure, but alone the effects on MeHg concentrations were muted. Importantly, we found a significant interactive effect of nutrients and temperature: the nutrient addition appeared to buffer against increased MeHg concentrations associated with elevated temperature. However, there was variability in this response, which seems to be related to the abundance of Daphnia and edible phytoplankton. Nutrients at low temperature were associated with marginal increases (1.1×) in zooplankton MeHg. Our findings suggest that global change drivers that influence community composition and ecosystem energetics of both zooplankton and phytoplankton can alter MeHg pathways through food webs.

Remote sensing of zooplankton swarms

Zooplankton provide the key link between primary production and higher levels of the marine food web and they play an important role in mediating carbon sequestration in the ocean. All commercially harvested fish species depend on zooplankton populations. However, spatio-temporal distributions of zooplankton are notoriously difficult to quantify from ships. We know that zooplankton can form large aggregations that visibly change the color of the sea, but the scale and mechanisms producing these features are poorly known. Here we show that large surface patches (>1000 km2) of the red colored copepod Calanus finmarchicus can be identified from satellite observations of ocean color. Such observations provide the most comprehensive view of the distribution of a zooplankton species to date, and alter our understanding of the behavior of this key zooplankton species. Moreover, our findings suggest that high concentrations of astaxanthin-rich zooplankton can degrade the performance of standard blue-green reflectance ratio algorithms in operational use for retrieving chlorophyll concentrations from ocean color remote sensing.

Biomass of plankton and macrobenthos and benthic species diversity in relation to environmental gradients in a nationwide coastal survey

Using Korean coastal survey data, we examined the relationships between plankton and benthic biomass and environmental parameters. The nitrate in coastal waters was mainly derived from the influx of fresh water, whereas much of the ammonium originated from decomposing organic matter in the sediments and river discharge. Phytoplankton and zooplankton concentrations were positively related to the amount of suspended particulate matter (SPM), but decline when SPM becomes high (> 10 ppm). Particulate organic carbon (POC) comprised about 40% of the SPM, suggesting that organic matters associated with river-borne sediments and re-suspended particles are a large source of coastal water POC. Zooplankton abundance was more closely related to the distribution of phytoplankton than to that of POC. Benthic biomass showed a dome-shaped relationship with the water column POC concentration, but no clear relationship with sediment POC distribution. The biodiversity of macrobenthic animals gradually decreases when POC exceeds 1% of the sediment weight. Reduction of siltation and POC could lead to enhanced benthic–pelagic coupling via increased plankton biomass and productivity, as well as overall increased benthic diversity in coastal environments.

Effect of temperature on zooplankton vertical migration velocity

Zooplankton diel vertical migration (DVM) is an ecologically important process, affecting nutrient transport and trophic interactions. Available measurements of zooplankton displacement velocity during the DVM in the field are rare; therefore, it is not known which factors are key in driving this velocity. We measured the velocity of the migrating layer at sunset (upward bulk velocity) and sunrise (downwards velocity) in summer 2015 and 2016 in a lake using the backscatter strength (VBS) from an acoustic Doppler current profiler. We collected time series of temperature, relative change in light intensity chlorophyll-a concentration and zooplankton concentration. Our data show that upward velocities increased during the summer and were not enhanced by food, light intensity or by VBS, which is a proxy for zooplankton concentration and size. Upward velocities were strongly correlated with the water temperature in the migrating layer, suggesting that temperature could be a key factor controlling swimming activity. Downward velocities were constant, likely because Daphnia passively sink at sunrise, as suggested by our model of Daphnia sinking rate. Zooplankton migrations mediate trophic interactions and web food structure in pelagic ecosystems. An understanding of the potential environmental determinants of this behaviour is therefore essential to our knowledge of ecosystem functioning.

Environmental Drivers of Ranavirus in Free-Living Amphibians in Constructed Ponds

Amphibian ranaviruses occur globally, but we are only beginning to understand mechanisms for emergence. Ranaviruses are aquatic pathogens which can cause > 90% mortality in larvae of many aquatic-breeding amphibians, making them important focal host taxa. Host susceptibilities and virulence of ranaviruses have been studied extensively in controlled laboratory settings, but research is needed to identify drivers of infection in natural environments. Constructed ponds, essential components of wetland restoration, have been associated with higher ranavirus prevalence than natural ponds, posing a conundrum for conservation efforts, and emphasizing the need to understand potential drivers. In this study, we analyzed 4 years of Frog virus 3 prevalence and associated environmental parameters in populations of wood frogs (Lithobates sylvaticus) and green frogs (Lithobates clamitans) in a constructed pond system. High prevalence was best predicted by low temperature, high host density, low zooplankton concentrations, and Gosner stages approaching metamorphosis. This study identified important variables to measure in assessments of ranaviral infection risk in newly constructed ponds, including effects of zooplankton, which have not been previously quantified in natural settings. Examining factors mediating diseases in natural environments, particularly in managed conservation settings, is important to both validate laboratory findings in situ, and to inform future conservation planning, particularly in the context of adaptive management.

On biogenic turbulence production and mixing from vertically migrating zooplankton in lakes

Vertical mixing in lakes is a key driver of transport of ecologically important dissolved constituents, such as oxygen and nutrients. In this study we focus our attention on biomixing, which refers to the contribution of living organisms towards the turbulence and mixing of oceans and lakes. While several studies of biomixing in the ocean have been conducted, no in situ studies exist that assess the turbulence induced by freshwater zooplanktonic organisms under real environmental conditions. Here, turbulence is sampled during three different sampling days during the sunset diel vertical migration of Daphnia spp. in a small man-made lake. This common genus may create hydrodynamic disturbances in the lake interior where the thermal stratification usually suppresses the vertical diffusion. Concurrent biological sampling assessed the zooplankton vertical concentration profile. An acoustic-Doppler current profiler was also used to track zooplankton concentration and migration via the backscatter strength. Our datasets do not show biologically-enhanced dissipation rates of temperature variance and turbulent kinetic energy in the lake interior, despite Daphnia concentrations as high as 60 org. L−1. No large and significant turbulent patches were created within the migrating layer to generate irreversible mixing. This suggests that Daphnia do not affect the mixing in the lake at the organism concentrations observed here.

Performance of fish-habitat classifiers based on derived predictors from a coupled biophysical model

Abstract Fish habitat models based on remotely-sensed data may be limited by satellite coverage and availability. We compared the fit and predictive power of Random Forest habitat classifiers that were developed using predictors derived from a coupled biophysical model (i.e., modeled predictors) versus similar classifiers that used remotely-sensed satellite data for two data sets (eggs and adults) and four species that occur widely in the California Current system. When tested on independent data, classifiers of spawning habitat that used derived predictors (derived classifiers) had nearly identical accuracies (0–2% difference) to similar classifiers based on satellite data (satellite classifiers). Accuracies of derived classifiers of adult habitat were within −8% to +7% of comparable satellite classifiers. Accuracies of both types of classifiers on test data were much greater for Northern anchovy Engraulis mordax and Pacific hake Merluccius productus (0.75–0.97) than for jack mackerel Trachurus symmetricus and Pacific sardine Sardinops sagax (0.61–0.72), and generally were greater for classifiers of spawning habitat than for adult habitat. Specificity was very good for both types of classifiers, but sensitivity was poor, because classifiers identified potential habitat which was not fully occupied. Adults of all species used a broader range of habitat conditions during summer than during the spring spawning period. Derived classifiers have some advantages over satellite classifiers; they are not limited by cloud cover and they can make predictions in near real-time or the short-term future. However, there was no consistent improvement in the accuracy of derived predictors that included modeled zooplankton concentrations over comparable satellite classifiers that included reflectance/chlorophyll concentration.

Impact of Indian ocean dipole on the coastal upwelling features off the southwest coast of India

A three-dimensional regional ocean model is used to examine the impact of positive Indian ocean dipole (pIOD) events on the coastal upwelling features at the southwest coast of India (SWCI). Two model experiments are carried out with different surface boundary conditions that prevailed in the normal and pIOD years from 1982 to 2010. Model experiments demonstrate the weakening of coastal upwelling at the SWCI in the pIOD years. The reduced southward meridional wind stress off the SWCI leads to comparatively lower offshore Ekman transport during August–October in the pIOD years to that in normal years. The suppressed coastal upwelling results in warmer sea surface temperature and deeper thermocline in the pIOD years during June–September. The offshore spatial extent of upwelled colder (< 22 °C) water was up to 75.5° E in August–September in normal years that was limited up to 76.2° E in pIOD years. The heat budget analysis reveals the decreased contribution of vertical entrainment process to the mixed layer cooling in pIOD years which is almost half of that of normal years in October. The net heat flux term shows warming tendency during May–November with a higher magnitude (+ 0.4 °C day−1) in normal years than pIOD years (+ 0.28 °C day−1). The biological productivity is found to reduce during the pIOD years as the concentration of phytoplankton and zooplankton decreases over the region of coastal upwelling at SWCI. Nitrate concentration in the pIOD years dropped by half during August–September and dropped by an order of magnitude in October as compared to its ambient concentration of 13 μmol L−1 in normal years.

Effect of metals on zooplankton abundance and distribution in the coast of southwestern Taiwan.

Three transects were established along the southwestern coast of Taiwan; transects from north to south were respectively extended from the Kaohsiung Harbor, Kaoping River estuary, and Fangshan River estuary. Six metals including Pb, Cd, Cr, Cu, Zn, and Ni were analyzed in the zooplankton and seawater samples. A total of 24 groups of zooplankton were identified. Calanoid was the frequently collected group and accounted for greater than 40% of the relative abundance of zooplankton. Results showed that metal concentrations in seawater close to coast were higher than those in the outside of transect. The mean of metal concentrations in zooplankton followed the hierarchy: Zn > Cu > Pb > Ni > Cr > Cd. On the whole, metal concentrations in zooplankton from sampling sites in the coastal region were observed to be higher than those in the offshore region. The bioconcentration factor of zooplankton ranged within 103-105 for all studied metals and indicated that zooplankton in the seawater of southwestern Taiwan can accumulate metal even at background concentrations of metals. The value of diversity indices exhibited an increase in the distance to the coast, whereas the abundance showed no significant correlation with that. Consequently, the lowest mean abundance of zooplankton and the highest average metal bioaccumulation were found in transect outside Kaohsiung Harbor, representing that Kaohsiung Harbor has the contamination of anthropogenic metals that results in the impact on zooplankton.

БИОЛОГИЧЕСКАЯ ОЦЕНКА МАЛЫХ ВОДОЕМОВ, РАСПОЛОЖЕННЫХ В ПАРКОВЫХ ЗОНАХ ГОРОДА МОСКВЫ

The article describes the biological and ecological state of ponds of three park zones located in northern, central and western administrative districts of Moscow. The area of reservoirs varied from 0.12 to 3.71 ha, average depth varied from 1.12 to 2.4 m. The analysis of hydrobiological material in accordance with existing criteria has been carried out. Total and seasonal concentration and biomass of phytoplankton, zooplankton and benthos are determined. During observation period in composition of algocenosis prevailed representatives of following groups of algae: Volvocophyceae, Desmidiales, Bacillariophyta, Xanthophyta, Zygnematophyceae, Chrysophyta, Pyrrophyta, Protococcophyceae, Cyanophyta, Euglenophyta. Concentration of algae in ponds varied from 0.58 up to 6.78 mln/l, total biomass varied from 0.87 to 9.70 mg/l. Zooplankton of the inspected ponds was represented by species of three systematic groups: Rotatoria, Cladocera and Copepoda. Concentration of zooplankton organisms varied from 0.0055 to 3.9432 mln/m3, biomass varied from 0.05 to 18.60 g/m3. Zoobenthos included Oligochaeta, Clitellata and insect larvae (Chironomidae, Ephemeroptera, Trichoptera). Prevalence of various representatives of plankton groups depended on the season of the year. In zoobentos samples there were found oligochaeta, chironomid and mayfly larvae, caddisflies and leeches. Higher plants were represented by 8 hydrophytic species, 1 species with floating leaves and 10 aerial coastal species. Ichthyofauna of ponds included 12 species among which aborigen species were common carp, crucian carp, roach, bream, tench, verkhovka, Amur sleeper, pike, perch, pike-perch; invasive species were grass carp, silver carp. The investigations of the large Golytsinsky pond have demonstrated that episodic releases of silver carp (spotted and hybrid) make possible to utilize both zooplankton and phytoplankton, and release of grass carp helps utilize higher water plants.