Thermal tolerance of key-note macrofaunal species: a method to forecast the impact of climate change on African Mangrove systems

The principle of oxygen limitation of thermal tolerance in ectotherm (OLTT) theorises that the higher limits of an organism’ thermal niche are directly linked to its capability of maintaining an adequate provision of oxygen to its tissues. Initially inferred for marine ectotherms, the decline of thermal resistance due to inefficient tissue oxygenation, as expected by the OLTT, was shown also in terrestrial species. air-breathing ectotherms, however, showed wide thermal tolerances, since they could take advantage of the higher oxygen availability in air than in water. Here we tested the educated guess that bimodal species, such as intertidal invertebrates, could better cope with acute thermal stresses with respect to truly marine species, by taking advantage from air-breathing. Using intermittent flow-throw respirometry, we measured the metabolic rate of the rocky intertidal crab P. marmoratus along a temperature ramp procedure of 1°C × h-1 between 17-27 °C. We demonstrated that the oxygen consumption rates showed by P. marmoratus during aquatic and aerial respirations show the typical temperature-dependant exponential raise in water, while in air the aerobic metabolism remain unaltered. Our results demonstrate the ability of bimodal intertidal ectotherms to exploit both the aquatic and the aerial phases. This ability has to be taken into account in climate warming scenarios predicting about their present and future distribution and biology.