Aspects of the biology of Mytilocypris henricae (Chapman) (Crustacea, Ostracoda) with particular emphasis on salinity tolerance, life history and postembryonic ontogeny

Abstract

Three major apects of the biology of Mytilocypris henricae (Chapman ) are studied experimentally determined salinity tolerance and preference, the effects of postembryonal temperature ontogeny and salinity and growth on and the the population structure and dynamics of this species in Lake Bathurst (N.S.W.). Some notes on the effects of various factors upon hatching of eggs of this species are also added. Both temperature and salinity have a significant effect on survival of adults in direct transfer experiments, but there is no significant interaction between temperature and salinity. Similar experiments with stage 7 and 8 larvae prove that the upper tolerance limit of stage 7 larvae is much lower, while stage 8 larvae seem to react in a similar way as adults. M.henricae has 8 larval and 1 adult stage, as is usually the case in Cypridinae. A linear growth model is proposed and the implications on the interaction between Intermoult Period and Moult Increment are discussed. Temperature has a highly significant effect on the size (length, height) of the different larval stages, whereas the effect of salinity is not significant. However, both temperature and salinity have a highly significant effect on the shape of the shell (e.g. the lengthheight ratio) . The population of M. henricae in Lake Bathurst exhibited a continuous recruitment all lifestages were present in the samples throughout the year. There are three successive generations per year. Egg hatching in the lake seems to be more temperature dependent then is egg production. Salinity significantly affects egg hatching, although it appears that temperature is the major regulating factor. Orange eggs take longer to hatch than yellow eggs and might therefore be considered resting eggs. A review on the seasonal distribution of non-marine ostracods is given and a new classification of the different strategies is proposed.