Models of the bed structure dynamics of mass marine bivalves of the White Sea

Abstract

The present paper is a synthesis of all the results of long-term (for almost 35 years) observations of beds of nine widespread bivalve species, carried out at the Marine Biological Station of St. Petersburg State University in the White Sea (Chupa Inlet mouth, Kandalaksha Bay). The purpose of the investigations is to identify the patterns of the spatial-temporal organization of bivalve beds. As a result, a generalized analysis of the reasons for the spatial and temporal heterogeneity of the bed structure of widespread long-lived bivalve species in an undisturbed environment is presented, and attempts are made to develop models of the dynamics of the age structure of bivalve beds in the White Sea. An integrated approach to identifying the patterns in the organization of bivalve beds: the study of changes in the size-age structure of beds as a reflection of the recruitment, growth and mortality features, made it possible to identify intraspecific relationships as determining long-term trends in the structure changes of mollusk beds in the White Sea. Studies have shown that long-term stability of size-age structure is not a typical feature of the bivalve beds in the White Sea, and substantial fluctuations in their structure take place even under relatively undisturbed environmental conditions. The main reasons for the fluctuations of the bed structure appear to be connected to inter-annual variation in recruitment rates. These variations are mainly caused by the intensity of mollusks intraspecific interactions, and by the conditions of mollusk survival in the early stages of the life cycle. As a result of interannual fluctuations in the bed bivalve recruitment rates, specimens of only 1 or 2 generations dominated for several years. A periodic change of the dominant generations could be considered as a recurrence in the bed development. However, the recurrence of the bed structure dynamics can be easily disrupted under unfavorable conditions for the mollusk survival in the early stages of the life cycle. The bivalve stationary beds in the White Sea are likely the exception from the general rule. They can be formed in case of a relatively stable level of annual recruitment with a decrease in intensity of intraspecific competition. The latter in the White Sea beds of Bivalvia was observed either when the ecological needs of individuals of different ages were differentiated, or in the case of a relatively poor bed density.