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The process of climate change by which global temperatures increase and seasonal shifts occur is more pronounced at higher latitudes. These changes induce shifts in the phenology of biota, including zooplankton. Regression analysis revealed significant advance of the spring–summer water warming in the sub-Arctic White Sea (Chupa Inlet, Kandalaksha Bay), which occurs 3 weeks earlier in the last decade compared with 1961. The shift of timing of phenological events of Calanus glacialis, Pseudocalanus spp., Microsetella norvegica, Oithona similis, Acartia spp., Centropages hamatus, and Temora longicornis is particularly pronounced. These shifts were accompanied by a significant increase in Calanus and Microsetella abundance with an observed decrease in Acartia abundance. No correlation between population abundance and year-to-year changes in the species phenology was determined. We propose hypotheses to explain species adaptation to these phenological shifts in the ecosystem: (1) flexibility of life cycle of planktonic copepods, which ensures synchronization of life cycle phases with key events in the environment; and (2) copepod ability to switch to carnivory when algal sources are scarce. Interspecific interactions between ubiquitous species influenced their phenology and abundance, while early development of Microsetella caused later development of Oithona and higher abundance of the latter. We speculate that competition for food resources is a driving factor in the interactions, since the trophic niches of these species overlap.

Polar shallow marginal seas are of high importance as they are the most productive regions of the Arctic Ocean and serve as filters for terrestrial runoff. Salinity and turbidity gradients create diverse habitats for planktonic organisms in coastal areas. In the present study we aimed at assessing the degree to which environmental gradients influence the abundance and community structure of the zooplankton in a shallow Arctic sea affected by terrestrial runoff. Zooplankton distribution was studied in a coastal zone in the southeastern part of the Barents Sea (Pechora Sea) in July 2014 and September 2016 along the archipelago that stretches from the continent towards the open sea. The ecosystem was in a spring state in July (2014) and in a summer state in September (2016). A clear positive gradient of salinity and a negative cline of turbidity were revealed, directed from the coast towards the open sea. A horizontal salinity gradient was detected in both seasons. The turbidity gradient was most pronounced during summer. Distribution of several species of marine zooplankton (e.g. Pseudocalanus spp., Temora longicornis, Microsetella norvegica) was associated with the salinity gradient. Parameters of community structure (species richness, diversity, evenness, total zooplankton abundance) correlated with turbidity while only diversity and evenness were influenced by salinity. A gradient was observed from a more diverse and less abundant zooplankton community in areas with high turbidity and low salinity towards a less diverse and more abundant community in the open sea. This heterogeneity influences higher trophic levels including commercial fishes and reflects how marginal filters function.

Marine bivalves are well known for their impressive lifespans. Like trees, bivalves grow by accretion and record age and size throughout ontogeny in their shell. Bivalves, however, can form growth increments at several different periodicities depending on their local environment. Thus, establishing lifespans and growth rates of marine bivalves requires a proper identification of annual growth increments. Here, we use isotope sclerochronology to decipher the accretionary growth record of modern Astarte borealis from the White Sea, Russia (N 67°05.70′; E 32°40.85′). Unlike winter growth increments observed in many other cold-temperate and boreal bivalve and limpet species, prominent growth increments in A. borealis corresponded to the most negative values in the oxygen isotope (δ18O) time series indicating that they formed during summer. Furthermore, summer growth increments do not coincide with the external concentric ridges on the shell making the latter feature an unreliable indicator of age. Similar to many other polar bivalves, A. borealis shows slow growth and long life. The von Bertalanffy growth equation for our sample is Ht = 29.39*(1 − e(− 0.11(t−(− 1.86))). Lifespans of individuals examined here (n = 18) range from 16 to 48 years. Given its impressive longevity and widespread polar distribution, A. borealis may be a potentially valuable skeletal archive for monitoring environmental conditions in the Arctic Ocean and boreal seas in the face of changing climate.

Dense blue mussel assemblages are unstable, their structure changing from year to year. Three types of models can be used to describe this instability: (1) “exogenous” model based on regional temperature fluctuations, (2) “endogenous” deterministic model associated with negative impact of adult mussels on juveniles and (3) “density-linked stochasticity” model based on positive feedbacks resulting in overcrowding and destabilizing the settlement. We compared predictions deduced from these models with a time series based on the results of long-term (18 years) monitoring of abundance and demographic structure of three mussel beds at the White Sea. Most of our findings agreed well with the predictions deduced from the endogenous model. In particular, (1) long-term changes in mussel abundance and demographic structure were strictly cyclic, with non-matching periods (5–9 years) at different sites; (2) stages with the dominance of old mussels alternated with those where juveniles dominated and (3) some signals of delayed density dependence were revealed. However, the time series also contained elements of long-term trends, which may testify to the involvement of some exogenous factors (probably long-term climate changes).

The paper describes changing patterns of commercial fish catch in the downstream part of the Neva River and the eastern Gulf of Finland and analyzes drivers of these changes for the period 1929–1995. We summarize catch data on 20 species and species groups of fishes and lamprey, as well as available abiotic data (salinity, temperature and water transparency). Water transparency gradually decreased during the 20th century being inseparable from a number of non-quantified anthropogenic factors, thus it can be used as an integral index of anthropogenic loading on the ecosystem. Because fisheries statistics were not published regularly, catch data were extracted from archives and various publications. Fishing locations, gear and target species changed over time in relation to each other, reflecting technological developments in fisheries, commercial demands for fishery products and the abundance of fish populations. Until the 18–19th centuries, fisheries took place mostly in rivers where weirs and set nets targeted sturgeon, salmon and whitefish. By the end of the 19th century, herring and smelt were the main targets of fixed nets in coastal areas. A century later, the main commercial species, herring, was harvested with pelagic trawls operating offshore in the Gulf. This evolution in fisheries, along with other anthropogenic activities, caused severe declines in diadromous species. Spawning migrations that make them easy to catch, and their high market value, make diadromous fish more vulnerable than other groups. Canonical correspondence analysis showed that catches of most diadromous species decreased with increasing transparency, which may reflect their response to anthropogenic pressure. Marine and freshwater fish suffered from anthropogenic pressure, but to a lesser extent probably because of a wider distribution and dispersal, and more capital-intensive fishing methods. Catches of marine species, except herring, significantly increased in the 1970–1980s when salinity was comparatively high. We found no correlation of fish catches with temperature.

Populations of marine bivalves are known to be unstable but it is unclear whether this instability has internal or external causes. In this paper we summarize results from long-term (1978–2007) monitoring of an Astarte borealis (Astartidae) population in the White Sea. We sought significant long-term changes among a population of subtidal clams existing under relatively stable conditions. The studied population was initially (in 1978–1995) formed exclusively by adult clams, with no recruitment occurring until a mass inflow of unidentified astartid’s juveniles in the late 1990s. We assessed the suitability of periostracum microsculpture for identification of astartid juveniles and identified the juveniles recruited the population as A. borealis. Thus significant changes in population structure were detected. Our study suggests that A. borealis may have a very long life span (>20 years) and a prolonged recruitment failure could be associated with scarcity of hard substrates needed for egg attachment in a silted environment. As old clams died, their valves provided a hard substrate on the bottom surface, facilitating recruitment. We propose a new conceptual model of subtidal clams’ population dynamics predicting long-term cyclic changes driven by internal mechanisms associated with an unusual type of positive influence of adults upon recruits.