Thanatocoenoses of mollusc shells in the north-western part of the Black Sea

Abstract

Following death, mollusc shells become elements of thanatocoenoses of bottom and coastal deposits. At the early stages of succession of storm strands, the conservation of mollusc shells in the coastal deposits is high, which allows to obtain a larger number of shells to determine their traits. The probability of finding shells of rare mollusc species in the coastal strands is significantly higher than in bottom grab samples. Therefore, the taxonomic composition of the thanatocoenoses may correspond to the actual composition of mollusc assemblage in the adjacent coastal waters. Determination of the maximum age of molluscs from coastal emissions by sclerochronological methods can be more accurate characteristics of the lifespan of the considered mollusc species. Wind waves are one of the hydrodynamic processes influencing the formation of coastal emissions. The maximum wave activity in the coastal zone of the sea contributes to an increase in the deposition of storm emissions in the coastal zone. Studies of thanatocoenoses of marine molluscs in storm emissions in the north-western part of the Black Sea were carried out at three test sites, differing in the degree of wave load on the coastal zone. Analysis of coastal emissions in different parts of the coastal zone — various distance from the water's edge—allows us to determine the frequency and power of wave activity, as well as to identify the dominant species of macrozoobenthos in each area. The composition and quantitative characteristics of storm emissions created by wave activity of various intensities demonstrates the relationship between benthic biocoenoses of molluscs and thanatocoenoses of the coastal zone. The dominance of bivalve mollusc shells in emissions corresponds to the ruling species of molluscs in benthic biocoenoses. Shells of molluscs of the family Mytilidae were dominant in coastal emissions of the analysed areas. The maximum concentration of aquatic organisms is presented in emissions located near the edge of seawater. A dependence between the total mass of biogenic components in coastal sediments and different distances from the water edge has been revealed for the north-western part of the Black Sea.

Keywords

• black sea
• thanatocenosis
• bivalve mollusc shells
• storm strands