Results of the study of molluscs in the southern Primorye
18 November 2020

Results of the study of molluscs in the southern Primorye

Research by scientists at the Pacific branch of VNIRO has shown that the impact of typhoons on the state of aggregations of fishing shellfish and other hydrobionts is many times greater than the impact from their fishing.

The scientists of the Pacific branch of VNIRO have carried out surveys on the research vessel «Convinced» the state of the stocks of bottom molluscs, macrophytes and habitat in the coastal waters of the South Primorye.

According to the head of the expedition, Dmitry Sokolenko, more than 640 dive stations were carried out in the summer-autumn period in areas of more than 174 km2, taken for bioanalysis over 2.7 samples of hydrobionts and measured more than 12,000 samples.

Compared to previous studies, there has been an increase in the average density of both target and non-target grey hedgehogs in almost all areas from Krakovka to Eustafia Bay. The share of non-commercial grey hedgehogs increased from 61% in 2014 to 73% in 2020. At the same time, scientists do not exclude that the increase in the abundance of commercial individuals may be due to the formation of spawning clusters during the shooting period, which allow the animals to reproduce as successfully as possible. In the open Kievka Bay there was an increase in the spread area of spizula, but there was a decrease in abundance in the core of the cluster. The period of juvenile sedimentation this year, as in previous years, fell during the season of high Typhoon activity and heavy precipitation. As a result of storm surges and desalination of surface waters, juveniles are the most severely affected, but the high fertility and prolific spawning period of the speedola allows animals to replenish their numbers over time. In comparison with the data of 2016 the fishing stock decreased by 21%. In the warmer bivalve clams - mackerel and peronides, spawning and settling of larvae on the ground take place at a later date, so summer typhoons do less damage, but allow them to compete with the spiral for a living space. According to the present studies, there has been an increase in the size of settlements of these species and a twofold increase in stocks.

In Sokolov Bay, the habitats of coastal burying shellfish are partially protected from the disturbance of the southern rumbs by Orekhova Island, so the influence of typhoons is smoothed compared to the nearby Kievka Bay. There has been an increase in settlement areas and reserves as spizula and mactra.

In Rynda Bay (Russian Island), compared to data from many years of monitoring studies, there was an increase in the resources of Grey Mussel, Modiolus, oysters and Japanese scallop.

Diving surveys in the dreaded fishing areas of the anadar (kut part of the Amur Bay) and spizul (Boysman Bay) were carried out after the passage of the typhoon «Maysak». It is established that its influence on the state of clusters of commercial mollusks and other hydrobionts has been found to be many times greater than that of a decade-long fishery.

Extreme impacts of natural phenomena are not comparable to those of anthropogenic ones, the scientist stressed. At the same time, the destructive influence of natural elements and the recovery of coastal invertebrates depends on many factors, which require further study.

There have been no significant changes in the structure of algae and sea grasses in the studied areas outside Peter the Great Bay, and the localization of the main fishing clusters of macrophytes has not changed. However, it is noteworthy that the protected Rynda Bay has practically disappeared the thicket of laminarium algae saccharina of cichorioides.

Press Service VNIRO