14 January 2020
Oxygen loss in the world’s oceans, driven by climate change and nutrient pollution, is increasingly threatening fish species and disrupting ecosystems, according to a new report from the International Union for Conservation of Nature, or IUCN, released in December 2019 at the UN Climate Change conference in Madrid.
This report is the result of a global scientific effort that started in 2017 and is the largest peer-reviewed study so far into the causes, impacts, and possible solutions to ocean deoxygenation. LSU expert Nancy Rabalais, a professor in the Department of Oceanography & Coastal Sciences, authored chapters of the report concerning nutrient pollution and effects on coastal ocean ecosystems. Rabalais is well-known across the nation for her annual measurements of the hypoxic zone, a low-oxygen area along Louisiana’s coastline that is also known as the “dead zone.” The report states that as the ocean warms, the warmer water holds less soluble oxygen, which reduces the oxygen exchange between the atmosphere and the water. As this condition worsens, it will expand low oxygen zones in the open ocean and increase “dead zones” in coastal waters.
According to Rabalais, coastal deoxygenation is driven by eutrophication, a process by which increased nutrients (such as nitrate or phosphate from fertilizer runoff) in the ocean lead to algal blooms in which algae die and are then decomposed by bacteria. That decomposition process chokes the oxygen supply. This deoxygenation reduces habitats for many bottom-dwelling marine organisms. Those that can swim away do. Nevertheless, the remaining organisms, such as sponges, burrowing worms, and clams, eventually die. The loss of these bottom-dwellers means fewer food sources for larger marine organisms, reducing their population growth and forcing them to alter their migration patterns away from the low oxygen zones. While this process is not new—ecosystem degradation related to eutrophication and deoxygenation is evident in fossils found worldwide—it is accelerating.
The report concludes that while it may take centuries to recover fully, protecting marine ecosystems, improving wastewater treatment, and reducing fossil fuel combustion and agricultural runoff will improve local conditions and economies.
Rabalais has 34 years of experience studying deoxygenation in the Gulf of Mexico, joining LSU’s College of the Coast and Environment three years ago with prior experience at the Louisiana Universities Marine Consortium.
“LSU professors have been collaborators in our studies since 1985, but having a home at LSU brings even more recognition, I think, to this important research,” Rabalais said.
Rabalais lauds the IUCN report as a “great accomplishment” built upon sound science, concerted collaboration, and effective scientific communication. And, these three pillars extend to her LSU classroom. She says the most important thing she wants students to learn is how to “understand the science and be able to explain it to people in a coherent and comprehensive way. Because people need to understand. If you give them too much technical stuff, they are just going to turn off. You need to be able to communicate your science.”