Opposing physiological performances of two coexisting gastropods to changing ocean climate

The impact of climate change on the structure of ecological communities will be influenced by how different species respond to changing environmental conditions. In this study, we investigated the effects of increased temperature (summer Control, 21 °C; HT, 24 °C) and elevated CO₂ levels (Control, 400 ppm; OA, 1000 ppm) on two species of co-occurring temperate gastropods - Turbo undulatus and Austrocochlea odontis. Biological responses to simulated future conditions were measured as growth rates (shell and tissue) and metabolic rates across thermal ramps (temperatures ranging from 15 °C to 38 °C) after 8 weeks of exposure. We found that T. undulatus exposed to HT, OA or HT × OA conditions had a higher metabolic rate throughout their thermal curve than control conditions. In addition, the temperature at which individuals had maximum metabolic rate (T_MMR) was higher in animals acclimated to HT × OA than in other conditions, potentially demonstrating acclimation. In contrast, A. odontis showed antagonistic effects in response to OA and HT; metabolism was lowest under OA but highest under HT. Furthermore, T_MMR was reduced in A. odontis exposed to HT and the combination of HT x OA. In terms of growth, T. undulatus exposed to HT and HT × OA grew three times more in shell length and ∼20-30 % in weight compared to the control group or those exposed to only OA. In contrast, no treatment had a significant effect on growth in A. odontis. Overall, our findings suggest that the impact of ocean acidification and heating on metabolic function can differ between coexisting species, possibly depending on their evolutionary and life history strategies, and these differential responses could have significant implications for the structure of ecological communities.