Effects of Brood Viability and Rising Temperature on Oxygen Consumption of Freshwater Mussel Glochidia (Bivalvia: Unionidae)

Unionid mussels are imperiled worldwide. Understanding the impacts of thermal and hypoxia stress on larval (glochidia) and adult physiology is critical for understanding potential impacts of climate change. We tested whether brood viability (proportion of glochidia competent to attach to a host) was correlated with oxygen demand (MO2), ability to regulate oxygen consumption (RI), and/or critical dissolved oxygen concentration (DOcrit). We then examined effects of temperature on MO2, RI, and DOcrit. Results were coupled with a previous study to estimate the fraction of brooding female oxygen demand comprised of glochidial respiration. We found little evidence that respiratory patterns of glochidia changed with declining brood viability, but strong evidence for decreasing glochidial RI and increasing DOcrit with increasing temperatures. Glochidial respiration temperature coefficient (Q10) values were approximately 2-3x those estimated for brooding females, indicating greater temperature sensitivity. The proportion of gravid female respiration comprised of glochidial respiration reached its maximum at temperatures (23–28 °C) coinciding with brood expulsion. These patterns suggest high temperatures may have deleterious effects on unionids by decreasing hypoxia tolerance of glochidia, increasing the rate at which glochidia deplete energy reserves, and increasing the proportion of oxygen consumption by gravid females that is comprised of glochidial oxygen demand.