UC San Diego

Anthropogenic climate change, mostly induced by CO2 emissions, has been increasing temperature, while decreasing pH and dissolved oxygen (DO) in the ocean. Given that climate change will continue to exacerbate these conditions, it is important to understand how these changes will affect marine organisms, and consequently their ecosystems and economical value to humans. While there is substantial number of experimental studies that focus on temperature and pH stressors, DO has received comparatively little attention. Low DO, or hypoxia, can cause consistent negative impacts on marine fauna, and is a key factor of ocean change that warrants further study. Here, we developed an experimental flow-through system to expose red rock shrimp, Lysmata californica, to cyclic hypoxia for 31 days. This system permitted long-term exposure to fluctuating DO levels that mimic the natural conditions of their environment. After one month of exposure, we found that molt frequency, molt increment (body mass and carapace length), and exoskeleton mechanical properties (hardness and stiffness) were largely unaffected by the cyclic hypoxia treatments. Ours is one of the first to examine and determine the effects of DO on the mechanical properties of crustacean exoskeleton, and we emphasize the importance of mimicking natural oxygen fluctuations in laboratory experiments while taking into account the range of biological responses, from physiological adaptations to avoidance, to assess realistic organismal impacts. Cyclic hypoxia is a common natural phenomenon in coastal regions, and this study helps shed light on designing hypoxia experiments to better understand its consequences to species and coastal ecosystems.