Response of native and alien grazers to global warming: marine heatwaves vs gradual trends

Abstract

Abstract As extreme climatic events are increasing in frequency and intensity, ecological responses to global warming are likely to be driven by a combination of gradual warming trends and extreme climatic events. When extreme events (e.g., heatwaves) are added to ongoing warming, they may amplify its impact, resulting in complex ecological responses which are poorly known. Here, the effects of future gradual warming and marine heatwaves were compared, separately and in combination, on native and alien snail grazers (Cerithium lividulum and Cerithium scabridum, respectively), co-occurring in rocky intertidal pools along the Levantine coast. Survival and faecal production (as feeding rate proxy) of the two species were measured under four experimental temperature conditions: ambient (31°C), predicted warming scenario (ambient + 3°C), and short-term marine heatwaves (+ 5°C) on top of either ambient or warming treatments, followed by a recovery period. No effect of warming alone was detected on the two species whereas marine heatwave reduced faeces production only in C. lividulum. During the recovery period, C. lividulum survival dropped, but the few surviving individuals recovered from the heat stress as indicated by the increase in faecal production. Neither snail species survived under the combination of warming and marine heatwave. These results show that the two species, living in a thermally fluctuating and sometimes extreme environment, can handle a + 3°C warming but only the invasive snail can handle + 5°C. However, neither species can tolerate a strong heatwave on top of the predicted gradual warming, suggesting that both species will likely go extinct in the region.