Mortality of the mussel Mytilus galloprovincialis (Lamark, 1819) depending on sex

The mussel Mytilus galloprovincialis is one of the most popular species for cultivation globally and is one of the most abundant mollusc species in the Black Sea. In recent decades, there have been changes in the sex structures of the Black Sea settlements of M. galloprovincialis, trending towards an increase in the number of males. However, data on the effects of male and female mortality on the sex ratio in the population of M. galloprovincialis are insufficient. Therefore, this study aimed to assess how sex impacts the mortality of M. galloprovincialis. Mussels with shell lengths of either 30 or 55 mm were selected during the mass spring spawning. A total of 580 specimens were collected for the study. The separation of molluscs by sex was performed individually for each specimen via temperature stimulation of spawning. Each mussel was labelled according to its sex. The mortality of the mussels was studied in natural and laboratory experiments. In the natural experiment, different-sized females and males were selected and placed in cages that were hung in polluted harbour water. After 6 months, the number of dead mussels was recorded. In the laboratory experiment, sex-labelled mussels were placed in aquariums. The laboratory experiment was terminated after the death of 50% of the mussels. The mortality of females was found to be significantly higher than that of males. In the natural experiment, the mortality of females compared to males in the 55 mm size group was 23% higher and 18% higher in the 30 mm size group. In the laboratory experiment, the mortality of females in both size groups was 16% higher than that of males. Therefore, it was established that one of the reasons for the increase in the number of males in the settlements of M. galloprovincialis in the Black Sea is the higher mortality rate of females compared to males