Investigation of seasonal alterations of life in the upper sea zones of Southern Primorje by the quantitative diving method
© Biologischen Anstalt Helgoland 1973
1. Bottom biocoenoses in Possjet Bay (Sea of Japan) have been studied employing the quantitative diving method of hydrobiological investigation in different seasons of the year.
2. The investigations have revealed the existence of considerable seasonal successions in biocoenoses. These successions affect not only the number of populations and their age structure, but also influence the qualitative composition of the biocoenoses.
3. The responses are most pronounced in warm-water species; they initiate migrations preceding spawning in spring and summer, and torpor in the autumn-winter period. Migrations occur long before the temperature attains values necessary for successful reproduction, and long before it falls to the level causing torpor with cold. Apparently the primary factor initiating the migrations or changes in behaviour is the light.
4. Species of different biogeographical origin respond to definite temperatures for spawning and for settling of young.
5. The number of individuals per species undergoes considerable seasonal changes. Within the majority of species it reaches its maximum in summer and autumn, due to the appearance of the young, and its minimum in winter and spring, due to mass elimination.
6. The degree of seasonal changes in bottom biocoenoses of the upper regions of the shelf is highest in submerged plants; it diminishes in the following order: inhabitants of the phytal epifauna, animals with a short life cycle, animals with a long life cycle, vegetarian species, predators.
7. To a considerable extent, seasonal successions in biocoenoses depend upon fluctuations in biomass of the dominant background-forming species. Seasonal variations comprising 7 or 10 times larger or smaller biomasses are observed in biocoenoses in which the dominant background-forming species reveal pronounced changes in their biomass within a one-year period; relatively small seasonal variations (2 or 3 fold) are characteristic of biocoenoses with dominant species which are not background-forming or which change their biomass during the seasons only slightly.
8. Biocoenoses of the littoral zone change much more than biocoenoses located below the tidal level. Biocoenoses of the littoral zone and of shoals that are covered with a solid layer of ice during winter are less liable to seasonal successions than biocoenoses of open unprotected beaches that remain free from ice during the cold season or are intermittently covered with drift ice.
9. Before the cold season begins, warm-water species migrate from the littoral to depths below 0 m, form aggregations and fall into torpor with cold, when the temperature falls further. Cold-water species remain active in winter; some of them rise from more than 20 m to depths of about 2 or 3 m, temporarily joining the shoal biocoenoses. In some more changeable biocoenoses of the littoral, successions result in the substitution of the dominant forms.
10. All biocoenoses studied are stationary; in each season they exhibit a more or less definite number of species, biomass and specific composition.