S. M. Golubkov

Ecosystem changes in the Neva Estuary (Baltic Sea): natural dynamics or response to anthropogenic impacts?

The Neva Estuary situated in the eastern Gulf of Finland is one of the largest estuaries of the Baltic Sea with a large conurbation, St. Petersburg, situated on its coast. Eutrophication, alien species and large-scale digging and dumping of bottom sediment are the most prominent anthropogenic impacts on its ecosystem. However, many ecosystem responses, which are traditionally attribute to these impacts, are related to natural dynamics of the ecosystem. Fluctuations in discharge of the Neva River, intrusions of bottom hypoxic waters from the western part of the Gulf of Finland, higher summer temperatures and a shorter period of ice cover are climatic mediated factors inducing adverse changes in its ecosystem from the 1980s onwards. The main ecosystem responses to these factors are 2-3-fold increase of trophic status, deterioration of native zoobenthic communities and establishment of alien species, as well as the many fold decrease of fish catch and the population of ringed seal in the region.

Biodiversity and the functioning of hypersaline lake ecosystems from Crimea Peninsula (Black Sea)

Environmental variables, biodiversity-productivity relationships and energy pathways were investigated in six shallow lakes of the Crimea with salinity ranging from 24 to 429 g/l. The research included estimations of primary production and total phosphorus concentrations, evaluation of species composition and abundance of planktonic and benthic organisms. There were considerable inter- and intra-annual fluctuations in the abiotic characteristics of the lakes. All lakes had a very high concentration of total phosphorus in the water (up to 5.6 gP/m 3 ) due to a great influence of the watershed on the lakes. A high level of primary production (up to 14.9 gC m -2 d -1 ) was found in most of the lakes. The lowest primary production was in the most saline lake with a dense population of the filtrator, Artemia sp. There were weak negative relationships between the species richness of phytoplankton and the salinity, but species richness of zooplankton and zoobenthos was strongly negatively related to salt concentration. Positive relationships were found between the total number of planktonic and benthic species and primary production of plankton. Grazing benthic energy pathways were dominant at salinities between 25 and 62.5 g/l. Greater levels of salinity led to the gradual reduction of benthic and to an increase of planktonic energy pathways. There were strong positive relationships between species richness and the primary production of phytoplankton. Three different mechanisms are discussed that provide an explanation for this result. They are energy allocation for osmoregulation at high salinities, complementarity in resource utilization of phytoplankton species and trophic-cascade interactions in ecosystems.

SEDIMENT QUALITY ASSESSMENT USING GMELINOIDES FASCIATUS AND MONOPOREIA AFFINIS (AMPHIPODA, GAMMARIDEA) IN THE NORTHEASTERN BALTIC SEA

Crustaceans in the order Amphipoda are sensitive organisms for the assessment of sediment quality. In this work we performed 10-day toxicity tests on muddy sediments collected from a total of 29 sites in the Gulf of Finland, the Gulf of Riga and the Gulf of Bothnia (northeastern Baltic Sea) using Baltic Sea species such as the native amphipod Monoporeia affinis (Bousfield, 1989) and the invasive amphipod Gmelinoides fasciatus (Stebbing, 1899), and also compared these results with those of bioassays carried out using the standard test species, laboratory-cultivated amphipod Hyalella azteca (Saussure, 1858). The sediment samples (three cm of the upper layer) were collected by a GEMAX Dual Corer during the R/V “Aranda” cruises in August and September of 2009 and 2010. Toxicity of sediments in bioassays with M. affinis and G. fasciatus gave varied results depending on the amphipod species used. The lowest quality of sediments determined using M. affinis was recorded at sites located in the offshore and deepwater areas (60-100 m depths) of the Gulf of Finland characterized by hypoxic/anoxic conditions. Toxicity testing applying G. fasciatus showed that sediments at >50% of the study sites in the Gulf of Finland and in the Gulf of Riga can be assessed as highly contaminated. Males of G. fasciatus were significantly more sensitive to potential contamination in sediments than females. The lower survival of males under contaminant stress may result in a skewed sex ratio in natural populations and in a decline of reproduction success. The survival rate of G. fasciatus in the toxicity tests correlated positively with the Shannon diversity index (calculated for macrozoobenthos at the study sites), weight losses on ignition (%) in sediments, and it also showed a negative relation with the bottom water oxygen content (mg/l). The results suggest that G. fasciatus is the more sensitive species of the three amphipods tested and can be used as a indicator of sediment quality in the Baltic Sea and other water bodies.

Phosphorus excretion by bottom invertebrates of inland water bodies.

192 The phosphorus cycle is one of the main substance flows in ecosystems of inland water bodies, and its rate determines their biological productivity [1]. Mineral phosphorus excreted by bottom animals is important for ensuring the necessary level of primary production [2]. At the same time, there are few quantitative assesss ments of the intensity of the mineral phosphorus excretion by representatives of zoobenthos: only sevv eral species of bottom invertebrates have been investii gated in this respect [2–5]. The modern metabolic theory of ecology predicts that the intensity of the majority of functional characc teristics of animals on the individual and population levels of organization decrease with increasing body weight [6]. Therefore, the goal of this study was the estimation of the quantitative dependence of the intensity of the mineral phosphorus excretion on the body weight of different representatives of bottom anii mals. Investigations were carried out under laboratory conditions at temperatures of 12, 15, 20, and 21°C. The majority of measurements were carried out at 20– 21°C. Animals were collected in the oligotrophic Lake Krivoe (northern Karelia), the Neva Bay and the Gulf of Finland of the Baltic Sea (Leningrad oblast), and the eutrophic Lake Donghu (central China) [7]. Experiments were conducted in vessels from 50 to 800 ml in volume, depending on the animal sizes. The excretion of mineral phosphorus was estimated by the difference between its concentrations in the control and experimental vessels. The concentration of phoss phorus was determined by the molybdate method with the use of ascorbic acid as a reducer. To determine the general parameters of the dependence of the intensity of phosphorus excretion on the animal body weight at 20°C, all experimental data were recalculated for this temperature using the coefficient Q 10 , which is equal to 2.25 [8]. The intensity of phosphorus excretion by mollusks was calculated for dry weight without the shell. The intensity of phosphorus excretion was meaa sured in oligochaetes Limnodrilus hoffmeisteri Claa parède; bivalve mollusks Unio pictorum (L. The results of the measurement of the phosphorus excretion intensity (Ex, µg P/(mg dry weight h)) of bivalve mollusks, amphipods and, aquatic insect larvae are presented in Fig. 1. It can be seen that, in all groups of bottom animals, the intensity is reduced with increasing body weight (W, mg of dry weight), and its dependence on the body weight fits the following power equations: Unionidae Ех = …

A relative contribution of carbon from green tide algae Cladophora glomerata and Ulva intestinalis in the coastal food webs in the Neva Estuary (Baltic Sea)

We analyzed stable isotope composition of carbon and nitrogen of suspended organic matter (seston) and tissues of macroalgae, macroinvertebrates and fish from the coastal area of the highly eutrophic Neva Estuary to test a hypothesis that organic carbon of macroalgae Cladophora glomerata and Ulva intestinalis produced during green tides may be among primary sources supporting coastal food webs. The Stable Isotope Bayesian mixing model (SIAR) showed that consumers poorly use organic carbon produced by macroalgae. According to the results of SIAR modeling, benthic macroinvertebrates and fish mostly rely on pelagic derived carbon as a basal resource for their production. Only some species of macroinvertebrates consumed macroalgae. Fish used this resource directly consuming zooplankton or indirectly via benthic macroinvertebrates. This was consistent with the results of the gut content analysis, which revealed a high proportion of zooplankton in the guts of non-predatory fish.

Factors affecting the role of macrobenthos in pelagic-benthic coupling in the Neva Bay (eastern Gulf of Finland)

Long-term fluctuations in composition, biomass and functional patterns of benthic animal communities in Neva Bay, which became freshwater artificial lagoon in the middle 1980s due to construction of flood protection barrier (Dam), are depended on both natural and anthropogenic factors. The influence of natural climatic induced factors is evinced by periodic high increase in zoobenthic biomass with a dominance of small mollusks, Pisidiidae, in the eastern part of the bay near the delta of Neva River (the area with highest sedimentation rate of particulate organic matter) for the years of high run-of of Neva River. It is periodically succeeded by dominance of large mollusks, Unionidae, in the other parts of Neva Bay in the years of low run-of of Neva River. Progressive decrease in abundance of glacial relicts, Pallasea quadrispinosa, and increase of Oligochaeta worms was observed since the beginning of 20th Century probably due to an increase of eutrophication and organic pollution in the bay. Functional role of zoobenthic communities in decomposition of organic matter and regeneration of phosphorus in the bay was very high at the beginning of 1980psilas in the period of high river run-of. In that time their food consumption was much higher than primary production in Neva Bay and they decomposed the main portion of the particulate organic matter brought by the Neva River waters. The role of zoobenthos in decomposition of organic matter has decreased during the last two decades in a period of low run-of due to the shift of the dominance of small Pisidiidae to large Unionidae and increase of plankton primary production in the bay. Large scale digging and dumping of bottom sediments dealing with constructions of new lands and ports in the eastern part of Neva Bay, which began in 2006 and resulted in distribution of great amount of suspended particulate matters over the whole bay, negatively affects bottom animal communities decreasing their role in ldquomarginal filterrdquo of the Neva Estuary.

Excretion by Benthic Invertebrates as Important Source of Phosphorus in Oligotrophic Ecosystem (Lake Krivoe, Northern Russia)

We studied contribution of benthic invertebrates to the dissolved phosphates flux from the bottom sediments to the water in an oligotrophic lake (Lake Krivoe, near the White Sea biological station “Kartesh”, Northern European Russia) in 2009-2013 with the aim to quantify specific (among and within taxa), spatial (littoral and deep sites) and seasonal variability. The excretion rates (Pexc) of soluble reactive phosphorus (SRP) were estimated in experiment with dominating taxa of benthic invertebrates (amphipods, oligochaetes, mollusks, and chironomids), freshly collected from the lake. Mass-specific P excretion rate was calculated as Pexc divided by animal dry mass and further used for calculations of benthic P efflux rates. Also, in other experimental series with and without animals (amphipods) we measured extracellular alkaline phosphatase activity. The results showed that the SRP excretion rates varied significantly between taxa and between different-sized individuals within the same taxa (the SRP excretion rate elevates with an increase in individual weight). Notable spatial and seasonal differences in biomass of benthic animals and phosphorus released by them in the lake were found. The calculated phosphorus efflux by excretory activity of benthic animals was more intensive in littoral sites (up to 14.4 μmol m-2d-1 in July), that 7 times greater than maximum efflux in deep areas (2.2 μmol m-2d-1). The mobile burrowing animals (the amphipods Gammarus lacustris, Monoporeia affinis, and Gammaracanthus loricatus) are able to move from the bottom sediments to water and transfer the nutrient; they contributed 80 % of P flux caused by benthic excretion in the lake and affected the activity of the extracellular alkaline phosphatase, increasing its level in water

Origin of carbon in organic matter in the Neva estuary

Analysis of the isotopic composition of tissues of representatives of zoobenthos and organic matter of seston have shown that the major part of carbon participating in the biological turnover in the ecosystem of the upper part of the Neva estuary is of terrestrial origin. Obviously, it is discharged from the lake drainage area to the Lake Ladoga–Neva–Neva estuary system. The results have revealed an important role in aquatic ecosystems of the humid zone of allochthonous humic substances creating a supplementary stock of nutrients and enhancing the productivity of ecosystems. Detailed investigations of the role of various forms of allochthonous organic compounds of terrestrial origin are necessary for elaboration of efficient measures for alleviation of eutrophication of the Neva estuary.

The Effect of Weather Conditions on Eutrophication in the Neva River Estuary

Analysis of long-term data on chlorophyll a and total phosphorus concentrations, plankton primary production, organic matter mineralization, and weather conditions in the middle of summer in 2003–2017 revealed eutrophication processes in the Neva River estuary. Weather conditions in the region exerted a strong effect on organic matter prodaction and mineralization processes in the estuary. Rainy and cold summers of the recent years promoted massive development of algae due to increased washout of nutrients from the catchment area, but the rate of organic matter mineralization in the water column was reduced because of low water temperature.