Sexual structure of population and reproduction cycle of Echinogammarus olivii (Crustacea, Isopoda) in the fouling community of Odessa Bay (Black Sea)

摘要

The sexual structure of Echinogammarus olivii (Milne-Edwards, 1830) population in the fouling community of Odessa Bay (Black Sea)has been determined. It is shown that the annual dynamics of sexual structure is conditioned by the peculiarities of the breeding cycle of this species in the coastal fouling community. Throughout the year quantitative prevalence of females over males was recorded. E. olivii breeding process takes place throughout the year. Peakof the breeding of this species falls within the early spring when thewater temperature reaches 10 °C. During the period of mass reproduction of crustaceans, sex ratio in the population is aligned. In this time the number of ovigerous females reaches 96% of the total. At the end of mass reproduction process the previous generation of adults die. Males eliminate earlier than females. In this period up to six females fall on one male. In early summer, 79% of population of these crustaceans comprise young immature species. In late summer, E. olivii, avoiding overheating, migrate from the coastal zone in the deeper layers and less warmed water. In the autumn crustaceans return to the coastal zone of the sea. At the same time, they reach sexual maturity and are ready for a new cycle of reproduction. In the Black Sea this species can produce up to four generations per year. In winter, when water temperature is lower, sex ratio in the population of crustaceans is aligned again. Maximum absolute fertility of females E. olivii in the fouling community of Odessa Bay is equal to 31 eggs. The relationship of this parameter with length and weight of the crustaceans is shown. Coefficientsof the equations of the dependence of wet to dry weights of males, oviparous and non-oviparous females of E. olivii on their length are presented. Absolute fertility parameters growth with increasing size of crustaceans females has been detected.