Organisms living in coastal waters are exposed daily to low oxygen (low O₂) conditions.  Some animals adapt to low O₂ by increasing levels of the respiratory pigment that delivers O₂ to tissues. For example, humans produce higher concentrations of hemoglobin at high altitude where O₂ is limited than at sea level. Other organisms, such as deep-diving and hibernating animals, can lower their metabolism, reducing their need for O₂. Estuarine organisms rely on these and other strategies to tolerate hypoxia. Less well-recognized is that high levels of CO₂ naturally occur with hypoxia in coastal waters, causing significant acidification. Yet, virtually nothing is known about the combined effects of low O₂ and high CO₂ on estuarine species. In this research project we exposed economically important estuarine shrimp and crabs to combinations of low O₂ and high CO₂. We documented impacts of low O₂ on the expression, structure and O₂-binding properties of their respiratory pigment hemocyanin, as well as changes in aerobic metabolism and the energetically expensive process of protein synthesis. In addition, we showed that low O₂ impairs the ability of crustaceans to perform energetically demanding activity, simulated by walking on treadmills. However, we also found evidence that under some circumstances, the adverse impacts of low O₂ can be muted or reversed by the addition of high CO₂. With added CO₂ blue crabs could walk longer on a treadmill, mud crab hemocyanin could bind more tightly to O₂, and the expression of one form shrimp hemocyanin decreased compared to low O₂ alone controls. These studies demonstrated that high CO₂ often interferes with normal adaptations to low O₂ in estuarine crustaceans. However, we found evidence for mechanisms by which shrimp and crabs can cope with the frequent co-occurrence of high CO₂ and low O₂ in natural and aquaculture conditions. The work draws attention to the future vitality of shrimp and crab populations which, world-wide, form the basis of a multibillion-dollar seafood market. These results should also prove useful in understanding how these economically and ecologically important species will be impacted in a warming world.

While conducting this research, the PI Co-PI and their collaborator Dr. Darwin Jorgensen (Roanoke College) taught, trained and published with 14 undergraduate students, 7 graduate student and 1 postdoctoral fellow, helping to strengthen our Nation’s future scientific work force. Outcomes of the work were communicated through peer-reviewed publications (20), presentations at national and regional conferences (28) and professional seminars at colleges and universities around the US. While leading this research effort, Drs. L. and K. Burnett continued to serve Co-Directors of the College of Charleston’s NSF-funded REU Program, which focused on stimulating diversity of high school and college students majoring in STEM disciplines and promoting communication of science to public audiences.

Results of these studies were shared with representatives of two aquaculture programs in the US, the USDA Shrimp Farming consortium, three international farming consortia, and an international feed-manufacturing company in an effort to promote international scientific exchange. Protocols developed under this research project form the foundation for ongoing collaborations with South Carolina’s Department of Natural Resources to develop scientifically-sound regulations to protect and managing the State’s marine and estuarine species.

Last Modified: 05/06/2018
Modified by: Karen G Burnett