Heat Waves, Calcium, and Crayfish: Effects of multiple stressors on juvenile Northern Clearwater Crayfish (Faxonius propinquus) physiology

Abstract

Calcium concentrations in many freshwater ecosystems around the world are declining due to past acidification, forest logging, and atmospheric base cation declines. Although this prevalent stressor frequently co-occurs with additional stressors, multi-stressor impacts involving calcium in freshwater ecosystems are widely understudied. To summarise current knowledge on multi-stressor impacts involving calcium in freshwater ecosystems and to identify gaps in the literature, we conducted a scoping review. One of the gaps we found in the literature was research on multi-stressor impacts of calcium and temperature, and more specifically, calcium and heat waves. These two stressors often co-occur in freshwater ecosystems, and species such as crayfish, which are calcium-dependent and poikilothermic, are heavily impacted by both. We therefore conducted a laboratory experiment with a factorial design to examine the combined impacts of calcium declines and heat waves on a calcium-dependent species that is native to Ontario, the Northern Clearwater Crayfish (Faxonius propinquus). We examined impacts on survival, growth, and total body calcium content of juvenile specimens, and found that lower water calcium concentrations decreased total body calcium content, heat waves accelerated growth rate, and both stressors impacted survival. We did not observe interactive effects of water calcium concentrations and heat waves. These results are significant as they reveal how a species facing population declines responds to two commonly co-occurring stressors. Our results demonstrate the sensitivity of Northern Clearwater Crayfish to changes in temperature and calcium, which indicate the importance of addressing the sources of these stressors to prevent further population declines. Supplementary data for this thesis available at https://doi.org/10.5683/SP3/KHZMTJ