Effects of environmental factors on changing sex structure of cultivated mussels (Mytilus galloprovincialis, Lamarck, 1819) in the coastal zone of the Black Sea

Anthropogenically-induced stressors such as eutrophication and pollution cause fundamental changes of environmental factors in many coastal ecosystems worldwide and may subsequently alter the sex structure of bivalve populations. Such a change of sex structure was observed in the mussel Mytilus galloprovincialis at the Black Sea coast of Crimea, where the sex ratio shifted toward male mussels. This pattern may be caused by the sex inversion in females, higher female mortality, and their falling off to the bottom. Experiments with cultivated mussels M. galloprovincialis were conducted in natural and laboratory conditions to identify the reasons for this phenomenon. The inversion of the mussel sex proceeds in one direction: from females to males. The change of sex occurs under the influence of environmental factors during the post-spawning restructuring of gonads. Such factors can be adverse hydrological and hydrochemical conditions; environmental pollution; food availability; age and size of mollusks. The sex inversion of mussels in the polluted water area was 20% higher than in the relatively clean water of the mussel farm. The higher mortality of mussel females (69%) in the polluted area as compared to the clean one (19%) was also observed. In a laboratory experiment, the mortality level of females was 34% higher than that of males. The sex ratio on the farm, 1:2.9 (♀:♂), and on the bottom under the farm, 2.6:1 (♀:♂), was found, and the predominance of females at the bottom under the farm was noted. A bias in the sex structure in one direction—from females to males—can have economic implications in aquaculture as well as ecological significance. The increasing anthropogenic impacts on natural mussel populations can cause abnormal bias of sex ratio.