Abstract:
Temperature is an extremely important factor in determining both the physiology and distribution of an organism. Under future climate change it is predicted that increases in both mean temperatures and the frequency and severity of extreme high temperature events will occur. Due to the extremely heterogeneous nature of intertidal environments it is essential that we gain a more mechanistic understanding of population responses to increased temperatures so that more accurate forecasts can be made about the future population dynamics of intertidal species in response to climate change. Accordingly, this study reports the first measures of thermal tolerance for the marine gastropod mollusc, Lunella smaragda from six sites (three east coast sites & three west coast sites) within the Auckland region. The main objective was to determine whether east coast populations are more thermally tolerant than their west coast conspecifics as a result of differing spring tidal regimes. Based on temperature logger data, it was established that the rocky intertidal east coast sites reached significantly higher emersion-associated maximal temperatures than the west coast sites. Thermal tolerance proxies for L. smaragda were then determined on the basis of four phenotypic assays measuring survival ability, attachment ability, oxygen consumption and anaerobic enzyme activity in response to thermal stress. The results from these assays showed no differences between the east and west coast populations suggesting that despite the significant differences in the high emersion-associated maximal temperatures found between the two coasts, east coast populations of L. smaragda are currently no more thermally tolerant than west coast populations. However, the fact that temperatures recorded at the east coast sites exceeded the recorded LT50 values for L. smaragda, gives a strong indication that the east coast populations can be expected to routinely experience temperatures that exceed their upper thermal tolerance limits. Therefore, compared to west coast populations, east coast populations may be on the cusp of a tipping point and potentially suffer greater deleterious effects under predicted climate change than west coast populations.
