Short‐Term Responses of Native (Perna viridis, Linnaeus 1758) and Non‐Native (Mytella strigata, Hanley 1843) Mussels to Independent and Combined Effects of Lowered pH Level and Elevated Temperature

ABSTRACT

Changes in environmental conditions can influence the success of marine biological invasions. This study assessed the independent and combined acute short‐term effects of increased temperature (OW) and lowered pH (OA) simulating future ocean conditions on a native, Perna viridis, and non‐native, Mytella strigata, mussel species. There were four treatment combinations: Future (combination of ocean warming and ocean acidification), Ambient conditions, ocean acidification (OA), and ocean warming (OW). Survival and byssus thread regeneration in all treatments were measured daily for 7 days, while net calcification rate was calculated from the start and end of the experiment. Net calcification rate (NCR) was lowest under OA treatment. Likewise the low total alkalinity at the start of the experiment under OA suggests that the mussels experienced greater physiological stress. The higher survival rate of green mussels and the increase in the byssus regeneration rate over time in all treatments demonstrated that it can acclimate better to acute short‐term temperature and pH stress. The very low survival of M. strigata in OA compared to other treatments indicates its high sensitivity to low pH stress. However, surviving charru individuals maintained high byssus thread regeneration in all treatments. Overall, results suggest that M. strigata may not displace the native green mussels', P. viridis, higher tolerance to acute short‐term exposure to elevated temperatures and low pH, but can co‐exist in lower densities. This is the first study to compare the short‐term physiological responses of a sympatric non‐native and native mussel species under experimentally induced stress conditions. Longer‐term studies on the population dynamics of these species are essential to assess the potential success of these species under changing and variable environmental conditions.