An ontogenetic approach to the thermal response of mangrove macro-benthos: explaining processes in endangered coastal systems under global change

Rapid climate change has a strong impact on marine ecosystems, through warming, acidification, hypoxia and salinisation of sea water. Marine ectotherms are mostly affected by changes in temperature, which directly influence oxygen availability and their ability to utilize oxygen with potential cascading effects on their overall fitness. As a consequence, understanding the thermal response of organisms, especially in ecosystem engineers, is crucial to forecasting the effects of climate warming on ecosystem functionality. Here we focus on the thermal tolerance of two mangrove ecosystem engineers inhabiting the eulittoral zone of East African and South African mangrove forests, the crabs Perisesarma guttatum (Sesarmidae) and Uca urvillei (Ocipodidae). In order to assess their sensitivity to acute temperature fluctuations across a wide latitudinal gradient, we studied the thermal window of a Kenyan and a South African population of each species at different life stages: eggs, larvae (zoea) and adults. The metabolic rates were measured in the laboratory along a temperature ramp procedure of 1°C × h-1 between 17-37°C. The measures were performed in air and water for the adults and eggs, as these two stages experience both conditions, and just in water for the larvae. For the adults we used an intermittent flow-throw respirometry and for eggs and larvae a closed respiratory micro-chamber. Preliminary results show different thermal response for adults of both species at different latitudinal range, while results for eggs and larvae are still on progress. Further analysis have to be conducted in order to draw a complete and clarifying scenario on thermal biology of these species as oxygen saturation in adult haemolymph and heart rate in eggs and larvae. Evaluate the thermal niche of different life stage of bimodal breather marine ectotherms are important because we could retrieve information about their plasticity and so their vulnerability facing current environmental change. Sensitiveness of macrobenthos is crucial to understand ecological dynamics in mangrove ecosystem functioning.