Moulting, survival and calcification: the effects of temperature and waterchemistry on an ostracod crustacean (Herpetocypris intermedia) under experimental conditions

Temperature and water chemistry are usually considered as being the two mai n factors to influence the development and survival of non-marine ostracods . These factors may act upon a wide range of biological parameters, among w hich, those directly linked to the moulting process are of great importance . In this work, we study the effects of water temperature and ionic composi tion on survival, moulting success and calcification in the freshwater ostr acod Herpetocypris intermedia; we propose a hypothesis on the basis of our general understanding of crustacean physiology to derive a tentative explan ation of the ecology and distribution of non-marine ostracods. Several temp eratures and water chemistries were used for experimental cultures of the a dult and juvenile stages of H. intermedia, in which survival, moulting and shell Ca-uptake were monitored. Water temperatures between 15 degrees C and 20 degrees C resulted in the longest survival times, but high water temper atures (20-24 degrees C) provided the highest rates of moulting and calcifi cation and shortest intermoult times. Despite this, the highest water tempe rature (24 degrees C) was associated with the shortest survival times, whil st survival time and calcification were low at the lowest temperature exami ned (13 degrees C). The different effects of ionic composition upon the bio logical parameters studied show that H. intermedia develops "better" in bic arbonate-rich than in chloride-rich waters. These experimental findings are in general agreement with field data and allow us to establish different t olerance limits and niche preferences for various congeneric taxa. Taking i nto account previously published data on calcium incorpora tion and ionic r egulation in freshwater Crustacea, our results suggest that there is a trad e-off between calcification and ionic regulation in non-marine ostracods; t hese animals need to precipitate calcite and also to pump bicarbonate ions outwards to maintain internal chloride concentrations. In recent times, wat er ionic ratios, and particularly bicarbonate/chloride ratios, have been co nsidered to be major factors influencing non-marine ostracod distributions. In this sense, the physiological mechanisms cited in this study to explain our experimental results would also illustrate the major biogeographic and ecological patterns observed in non-marine Ostracoda, i.e. that some speci es are restricted to brackish waters whilst others dwell only in freshwater s.