title: Effect of tidal regime on the thermal tolerance of the marine gastropod Lunella smaragda (Gmelin 1791).
abstract: The tidal cycle around New Zealand results in spring low tides consistently occurring during the hottest part of the day (mid-afternoon) in north-eastern New Zealand, and during the cooler dawn/dusk periods in the north-west of the country. We hypothesised that due to mid-afternoon spring low tides, intertidal populations residing at north-eastern sites would show greater thermotolerance than their north-west conspecifics. To test this we used the marine gastropod, Lunella smaragda, which were collected from sites on both the East and West coasts of the Auckland region and exposed to an acute heat shock. Thermotolerance was measured as survivorship (LT50), drop down time (time to heat coma) and thermal stability of the anaerobic energy producing enzyme Tauropine dehydrogenase. Furthermore, temperature loggers were deployed at each site so as to record and compare thermal regimes among sites. A strong temperature spike associated with spring low tide was found at all sites, and maximal temperatures of all East coast sites were higher than West coast sites (in some case by up to 10°C). In terms of thermotolerance, mortality of L. smaragda occurred at 42°C leading to 100% mortality at 45°C. However, comparison of LT50 showed snails were equally thermotolerant regardless of site of collection. Similar results were found in TDH thermal stability with animals from all sites showing an approximately 80% decrease in enzyme activity after 10min exposure to 42°C. Whilst drop down times were different among sites these were correlated with animal size as opposed to site of collection. Thus, East coast populations of L. smaragda appear no more thermotolerant than their West coast counterparts. Such a result is concerning as maximal temperatures at East coast sites already exceed the LT50 values of L. smaragda recorded in the lab suggesting these populations have less of a thermal safety margin.
authors: School of Biological Sciences, The University of Auckland, Private Bag 92019, Auckland 1010, New Zealand.
authors: B J D
authors: BJ
authors: Mortensen
authors: School of Biological Sciences, The University of Auckland, Private Bag 92019, Auckland 1010, New Zealand; Institute of Marine Sciences, The University of Auckland, Private Bag 92019, Auckland 1010, New Zealand. Electronic address: b.dunphy@auckland.ac.nz.
authors: B J
authors: BJ
authors: Dunphy
mesh_terms: D000064:Acclimatization; D000818:Animals; D004795:Enzyme Stability; D018869:Heat-Shock Response; D006358:Hot Temperature; D009520:New Zealand; D012621:Seasons; D012908:Snails / Q000201:enzymology / Q000502:physiology*; D013696:Temperature
keywords: Climate change; Enzyme; Heat coma; Local adaptation; Spring tides; Thermal tolerance