Osmoregulation and survival of two mysid species of Tenagomysis in southern estuaries of New Zealand

Abstract

The mysid shrimps Tenagomysis chiltoni and T. novaezealandiae are abundant in southern New Zealand estuaries; however, little is known of their osmoregulatory capacity and survival. We investigated their osmoregulation and survival under salinities of 0, 5, 10, 15, 20, 25, 30 and 33 at 5°C and 20°C, to evaluate if the variation in salinity limits their distribution in estuaries. T. chiltoni and T. novaezealandiae maintained species-specific haemolymph concentrations across the salinities tested. According to AIC model selection statistics, for osmoregulatory capacity, the combined effects of salinity and temperature emerged as the most parsimonious. For survival, the non-linear effect of salinity was found as the most supported model given the data. Mortality of T. chiltoni and T. novaezealandiae increased towards the extremes of fresh and salt water but was lower in intermediate salinities (10–25). The ability of these species to osmoregulate and survive were limited at 5°C, but improved at 20°C. Life-history stage was found to be critical for explaining the variations in survival. We concluded that salinity could influence osmoregulation and survival of Tenagomysis spp., and when interacting with temperature and life-history stage, may partly explain why both shrimp species could be found in intermediate salinities and why T. chiltoni is more prevalent in the upper reaches of southern New Zealand estuaries.