Vol 49, No 6 (2023)

The presented data on distribution of cartilaginous fishes in the northern Pacific Ocean show that the core of the fauna of the Emperor Seamount Chain includes Indo-West Pacific species that inhabited the ridge from the coast of Asia. Epipelagic species are not permanent residents of the region, but annually migrate from the mainland to the ocean together with common abundant fish species that form their food supply. Sharks and chimaeras of the meso-benthopelagic zone constitute the basis of permanent cartilaginous fish communities of the seamounts of the Northwestern Pacific. Representatives of the lower meso-benthopelagic zone populated the Hawaiian and Emperor Seamount Chains along with the Markus-Necker Ridge. Less deep-sea, but adapted to a fairly long-term dwelling in the water column in the adult state, the species of the upper meso-benthopelagic zone, spreading towards the ridge, covered a distance of about 3000 km in the pelagic zone. Probably, some sharks of the lower meso-benthopelagic zone could inhabit the underwater mountains of the Emperor Seamount Chain in the same way. The low endemicity of cartilaginous fishes in the considered area (5%) and the presence of identical and closely related species in southern Japan do not allow us to regard migrations to the Emperor ridge as rare, with the exception of sharks of the genera Squalus and Centroscyllium, which diverged on the seamounts to the level of new species.

The species structure of the dominant community of unicellular algae inhabiting the spawning and feeding salmon lake was studied in the Kurile Lake (southern Kamchatka peninsula). It has been shown that this structure is well described by the Motomura model. The geometric progression coefficient does not differ significantly from the value prescribed by the model, which is based on the stochastic remainder hypothesis. Several integral indicators characterizing the species structure have been calculated. The study has revealed some typical and unusual correlations between these integral indices. Inter-annual and intra-annual cyclical fluctuations in the value of indicators have been found.

An experiment was set up to estimate the rate of zooplankton consumption by the three-spined stickleback Gasterosteus aculeatus (Linnaeus, 1758) at different predator densities. A differential equation describes the dynamics of zooplankton abundance depending on duration of predator feeding. The derived function accurately characterizes the rate of zooplankton consumption by stickleback in the experiment, demonstrating a good agreement between the theoretical prerequisites and the experimental results. The relationship between changing a number of prey during predation, its mortality and consumption rate was revealed. The hypothesis of consumption rate proportional to the number of predators was tested. A comparative analysis of ingestion rate as a function of time and a function of prey density was performed.

New data have been obtained on the distribution of prokaryotic plankton and pelagic viruses in the Fram Strait (the Greenland Sea) during the polar night (late November). Three main types of water masses were present in the study area: surface polar, Atlantic, and transformed Atlantic. The content of mineral biogenic elements increased with depth. The concentration of chlorophyll a had low values (0.07–0.13 mg/m³). The abundance and biomass of prokaryotes varied from 286 000 to 675 000 cells/mL and from 2.7 to 11.7 mg C/m³, respectively. The composition of prokaryotic plankton was dominated by single small cells (more than 97% of the abundance and more than 68% of the biomass). The average cell volume was 0.034–0.096 µm³. The number of viruses varied from 724 000 to 3 920 000 particles/mL, and the biomass varied from 0.040 to 0.216 μg C/m³. Against the background of local maxima in the abundance of prokaryotic plankton in the 0–25 m layer, the highest concentrations of viruses were noted in the surface layer. In the latitudinal distribution (from south to north), an increase in the number of viruses and prokaryotes was revealed. A close relationship between their abundance and biomass with hydrological parameters and phosphate content was established; the role of certain water masses in the vertical distribution of microbes was insignificant. The relatively high abundance of viruses and prokaryotes indicated their significant activity during the polar night.