Biologiya Morya

Some aspects of the reproductive biology of the widespread boreal hermit crab Pagurus middendorffii Brandt, 1851 were studied. Samples were collected monthly from November 2022 to November 2023 at a depth of 1–3 m in Zhitkov Bay (Russky Island, Peter the Great Bay, Sea of Japan). About 38% of the specimens were infected with parasitic crustaceans. Among healthy hermit crabs, the size of the calcified part of the carapace (SL) ranged from 1.9 to 6.6 mm (average 4.53±0.95) for males, from 1.9 to 5.5 mm (average 3.67±0.68) for females, and from 1.9 to 5.3 mm (average 3.56±0.62 mm) for ovigerous females. The male to female ratio during the study period varied from 0.6 to 4.0 with an average of 2.2. Spawning commenced in late October and ceased in late November, the incubation period lasted 6.5 months, and the embryonic diapause was absent. Repeated spawning was not observed. A comparative analysis of the reproductive characteristics of hermit crabs from different areas showed that changes in the temperature regime influence the timing of spawning and the duration of the incubation period, which significantly increases due to the slow embryo development at low temperatures in some species and due to the embryonic diapause in others.

An integrated hydrological and microbiological survey of Amur Bay in July 2022 showed that the levels and distribution of values of the thermohaline and hydrochemical parameters indicate the effect of the summer monsoon and river runoff. Under southerly winds, there was a setdown of the water surface along the western coast, which resulted in a decrease in temperature by 0.3–1°C and an increase in salinity by 2.6 psu relative to those near the eastern coast. At the same time, a setup effect with blocking of freshened and warm, nutrient-enriched surface waters was observed in the northeastern part of the bay. These favorable conditions caused phytoplankton blooms accompanied by high concentrations of chlorophyll a (up to 6–9 µg/L) and oxygen saturation of water (up to 120%). In the near-bottom layers of this sector, hypoxia with oxygen concentrations lower than 5% was observed as a consequence of developing eutrophication. According to the results of microbiological testing, the waters of Amur Bay in the summer of 2022 were classified as mesosaprobic, enriched in organic compounds, with accumulation of organic matter prevailing over its degradation. The biological pollution of water was evidenced by a high abundance of bacteria of the sanitary indicator group, which exceeded the maximum permissible concentration; the activity of plant communities was indicated by a high abundance of phenol-resistant microorganisms. Oil pollution was detected only in vicinities of sources of petroleum hydrocarbons: an oil terminal and a junction railway station. The low abundance of metal-resistant microorganisms indicated the insignificance of specialized (technogenic) pressure on the waters of the bay by the sampling time.

The distribution of the Japanese sandfish Arctoscopus japonicus (Steindachner, 1881) in the coastal zone of Sakhalin Island in May–October 1998–2022 is described on the basis of materials of beach seine and set gillnet surveys. In the Tatar Strait, off the southeastern coast of the island, and in Aniva Bay, the Japanese sandfish is shown to be a common species but with low abundance, accounting for less than 1% of numbers and biomass in catches during the summer months. Aggregations with the highest density are formed by juveniles in July–August and by spawning adults in September. The coastal area is dominated by 3–5-year-old fish up to 21 cm in length; individuals aged 6+ yr and up to 27 cm in length have also been recorded.