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

Abstract

Temperature and water chemistry are usually considered as being the two main factors to influence the development and survival of non-marine ostracods. These factors may act upon a wide range of biological parameters, among which, those directly linked to the moulting process are of great importance. In this work, we study the effects of water temperature and ionic composition on survival, moulting success and calcification in the freshwater ostracod Herpetocypris intermedia; we propose a hypothesis on the basis of our general understanding of crustacean physiology to derive a tentative explanation of the ecology and distribution of non-marine ostracods. Several temperatures and water chemistries were used for experimental cultures of the adult 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 temperatures (20-24 degrees C) provided the highest rates of moulting and calcification and shortest intermoult times. Despite this, the highest water temperature (24 degrees C) was associated with the shortest survival times, whilst survival time and calcification were low at the lowest temperature examined (13 degrees C). The different effects of ionic composition upon the biological parameters studied show that H. intermedia develops "better" in bicarbonate-rich than in chloride-rich waters. These experimental findings are in general agreement with field data and allow us to establish different tolerance limits and niche preferences for various congeneric taxa. Taking into account previously published data on calcium incorpora tion and ionic regulation in freshwater Crustacea, our results suggest that there is a trade-off between calcification and ionic regulation in non-marine ostracods; these animals need to precipitate calcite and also to pump bicarbonate ions outwards to maintain internal chloride concentrations. In recent times, water ionic ratios, and particularly bicarbonate/chloride ratios, have been considered 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 species are restricted to brackish waters whilst others dwell only in freshwaters