Estimating long-term survival temperatures at the assemblage level in the marine environment: towards macrophysiology.

Defining ecologically relevant upper temperature limits of species is important in the context of environmental change. The approach used in the present paper estimates the relationship between rates of temperature change and upper temperature limits for survival in order to evaluate the maximum long-term survival temperature (Ts). This new approach integrates both the exposure time and the exposure temperature in the evaluation of temperature limits. Using data previously published for different temperate and Antarctic marine environments, we calculated Ts in each environment, which allowed us to calculate a new index: the Warming Allowance (WA). This index is defined as the maximum environmental temperature increase which an ectotherm in a given environment can tolerate, possibly with a decrease in performance but without endangering survival over seasonal or lifetime time-scales. It is calculated as the difference between maximum long-term survival temperature (Ts) and mean maximum habitat temperature. It provides a measure of how close a species, assemblage or fauna are living to their temperature limits for long-term survival and hence their vulnerability to environmental warming. In contrast to data for terrestrial environments showing that warming tolerance increases with latitude, results here for marine environments show a less clear pattern as the smallest WA value was for the Peru upwelling system. The method applied here, relating upper temperature limits to rate of experimental warming, has potential for wide application in the identification of faunas with little capacity to survive environmental warming.

Thermal limits of burrowing capacity are linked to oxygen availability and size in the Antarctic clam Laternula elliptica.

Animal responses to changing environments are most commonly studied in relation to temperature change. The current paradigm for marine ectotherms is that temperature limits are set through oxygen limitation. Oxygen limitation leads to progressive reductions in capacity to perform work or activity, and these are more important and proximate measures of a population's ability to survive. Here we measured the ability of a large Antarctic clam to rebury when removed from sediment at temperatures between -1.5 and 7.5 degrees C and at three oxygen concentrations, 10.2, 20.5 and 27.7%. The proportion of the population capable of reburying declined rapidly and linearly with temperature from around 65% at 0 degrees C to 0% at 6 degrees C in normoxia (20.5% O2). Decreasing oxygen to 10.2% reduced temperature limits for successful burial by around 2 degrees C, and increasing oxygen to 27.7% raised the limits by 1-1.5 degrees C. There was an interactive effect of body size and temperature on burying: the temperature limits of larger individuals were lower than smaller animals. Similarly, these size limits were increased by increasing oxygen availability. Considering data for all temperatures and oxygen levels, the fastest burying rates occurred at 3 degrees C, which is 2 degrees C above the maximum summer temperature at this site.