Chronic warming exposure enhances the potential of a marine copepod to persist under extreme heat events

ASLO Aquatic Sciences Meeting, Resilience and Recovery in Aquatic Systems, 4-9 June 2023, Palma de Mallorca, Spain

The study of the thermal tolerance and vital rates responses of a species can provide useful metrics to characterize its vulnerability to climate change. Under thermal stress, plastic and adaptive processes can adjust the physiology of organisms enhancing their tolerance and reducing the thermal sensitivity of metabolic processes. Yet, it is uncertain their actual capacity to expand the upper tolerance limits to an extent that allows to cope with rapid and extreme changes in environmental temperature. In this study, we reared the marine copepod <em>Paracartia grani</em> at control (19ºC) and warmer conditions (25ºC) for >18 generations and assessed their survival and fecundity under short-term exposure to a range of temperatures (11-34ºC). In the warm-reared copepods, the upper tolerance to acute exposure (24h) increased by 1-1.3ºC, although this enhancement was reduced to 0.3-0.8ºC after longer thermal stress (7d). Despite the high mortality at temperatures above 30ºC, the reproductive activity was sustained across the thermal range at both control and warm-reared conditions. No shift was observed in the thermal optimum and the critical thermal maximum of the egg production response; yet, the rates in the upper thermal range were up to 21.1-fold higher for the warm-reared animals. Our results show that the long-term exposure to warming enhanced the tolerance to stress temperatures and the fecundity of <em>P. grani</em>. Albeit of low magnitude, these changes improve the potential of the species to persist under extreme heat events