Effects of temperature and hypoxia on aerobic scope in the giant freshwater shrimps (Macrobrachium rosenbergii) and (Penaeus monodon)
Depending on future CO2 emission scenarios, the average surface temperature is projected to increase 1.1-6.4°C by 2100. Tropical species, compared to many temperate species, are expected to be particularly sensitive to elevated temperatures because they inhabit a relatively thermostable environment and are thought to be genetically adapted to this stability. Recently, two papers in the prestigious journal Science have identified reduced aerobic scope as the most important physiological threat to population survival imposed by global warming, and several studies present evidence suggesting that this is already happening in a number of temperate fish species. However, there is presently very little evidence in tropical species. We propose to use respirometry (oxygen uptake) to measure aerobic scope at different temperatures and to combine these measurements with analysis of individual metabolites (Lactate, succinate, amino acids etc), as well as detailed information on growth rates and protein synthesis. The measurements will allow us to determine the temperature at which tropical crustaceans show reduced Darwinian fitness and to answer the important question of whether the predicted temperature increases will have a significant impact on these economically important shrimp species.
Project Completion Report:
In light of the ongoing climate change, the ability to predict future effects on biota has received much attention, where it has been sought to establish a unifying model granting predictive power to characterize and quantify the sensitivity of species to global warming. The oxygen and capacity limited thermal tolerance (OCLTT) model proposes that thermo tolerance in all aquatic ectotherms is dictated by tissue oxygen supply, and that cardiorespiratory thermo-tolerance, therefore, is the main determinant of animal thermo tolerance. In this project we tested the validity of the OCLTT model by measuring the effect of temperature on a range of oxygen supply capacity parameters in three´crustacean species; the tropical Giant freshwater shrimp (Macrobrachium rosenbergii) and Giant tiger shrimp (Penaeus monodon) and the temperate European crayfish (Astacus astacus). The results show that the upper thermal limits in these species are not determined by limitations on the oxygen transport capacity of the cardiorespiratory system. We conclude that the OCLTT model is not universally applicable to all aquatic invertebrate species. M. rosenbergii, P. monodon and A. astacus appear to possess a cardiorespiratory system with sufficient thermal tolerance to maintain tissue oxygen supply until critical temperatures and other functions must therefore be responsible for upper thermal limits in these species.