Elevated seawater temperature, not CO, negatively affects post-spawning adult mussels () under food limitation.

Pre-spawning blue mussels () appear sensitive to elevated temperature and robust to elevated CO; however, the effects of these stressors soon after investing energy into spawning remain unknown. Furthermore, while studies suggest that elevated CO affects the byssal attachment strength of from southern latitudes, CO and temperature impacts on the byssus strength of other species at higher latitudes remain undocumented. In a 90 day laboratory experiment, we exposed post-spawning adult blue mussels () from Atlantic Canada to three CO levels (CO ~625, 1295 and 2440 μatm) at two different temperatures (16°C and 22°C) and assessed energetic reserves on Day 90, byssal attachment strength on Days 30 and 60, and condition index and mortality on Days 30, 60 and 90. Results indicated that glycogen content was negatively affected under elevated temperature, but protein, lipid, and overall energy content were unaffected. Reduced glycogen content under elevated temperature was associated with reduced condition index, reduced byssal thread attachment strength, and increased mortality; elevated CO had no effects. Overall, these results suggest that the glycogen reserves of post-spawning adult are sensitive to elevated temperature, and can result in reduced health and byssal attachment strength, leading to increased mortality. These results are similar to those reported for pre-spawning mussels and suggest that post-spawning blue mussels are tolerant to elevated CO and sensitive to elevated temperature. In contrast to previous studies, however, elevated did not affect byssus strength, suggesting that negative effects of elevated CO on byssus strength are not universal.