Respiratory Acclimation of Marine Fish to Ocean Deoxygenation

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Anthropogenic factors, including climate change, are increasing the prevalence of low-oxygen zones in oceans around the world (i.e., ocean deoxygenation), and this is especially true in the northern Gulf of Mexico where large seasonal oxygen minimum zones are common. Deoxygenation of coastal waters has serious implications for marine life, including the economically and ecologically important fish species endemic to these regions. It is hypothesized that the long-term survival of species subjected to this type of environmental change depend in part on their ability to acclimate by altering their physiology, a concept known as phenotypic plasticity. This proposal will use a combination of molecular biology, biochemistry, and whole-animal physiology to explore the ability of an economically important fish species, the red drum (Sciaenops ocellatus), to enhance respiratory oxygen uptake following exposure to prolonged periods of reduced oxygen availability. Results of this work will be incorporated into public education initiatives targeting K-12 students. The goal of these efforts will be to increase the scientific literacy of youth and the general public with an emphasis on understanding the core principles of ocean health, climate change, and the importance of healthy oceans and fish populations for coastal communities. In addition, mentored research training in integrative physiology will be provided for several undergraduate and graduate students and a post-doctoral fellow. The primary objective of this work is to explore the physiological mechanisms and ecological significance of respiratory plasticity in a representative marine fish, the red drum, exposed to prolonged environmental hypoxia. These exposures will occur above the critical oxygen threshold for the species, and the capacity of red drum to maximize aerobic scope, which would increase the capacity for ecologically important activities, will be assessed. This work integrates across multiple levels of organization by first exploring plasticity in the red blood cells, heart and red muscle using gene expression and biochemistry, after which whole-animal performance will be measured. The project addresses the following hypotheses related to hypoxia exposure: 1) fish will exhibit an altered pattern of hemoglobin expression coincident with elevated red blood cell and plasma accessible carbonic anhydrase that will work cooperatively to enhance oxygen offloading in the heart and muscle; 2) the heart and muscle will exhibit reduced mitochondrial proton leak, thereby generating more energy per unit oxygen; 3) acclimation will result in increased swimming performance and aerobic scope at the organismal level; 4) red drum exposed to reduced oxygen levels at early life stages will exhibit rigid phenotypic plasticity that results in altered phenotypes later in life. This comprehensive evaluation will provide invaluable insight into the ability of marine fishes to offset the deleterious effects of ocean deoxygenation on respiratory performance. These activities will also contribute to graduate and undergraduate student and post-doctoral training, and results will be integrated into public education initiatives focused on implications of climate change and ocean deoxygenation on marine life. This award was co-funded by the GEO-Division of Ocean Sciences Biological Oceanography Program and the BIO-Division of Integrative Organismal Systems Physiological Mechanisms and Biomechanics Program.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.