Sawyer: The problem of hypoxia

 Gulf of Mexico Hypoxia in 2011. Image from NOAA data, available on Wikipedia.

Gulf of Mexico Hypoxia in 2011. Image from NOAA data, available on Wikipedia.

Around the world, coastal communities rely on the marine ecosystem by way of fisheries, tourism, culture, history, and recreation. They shape how societies interact and how the economy flows. In some places, they are defining features of what it means to live and/or originate from that region; it’s a part of life for millions. But the natural world is all connected, with events happening in one part of the world and trickling down to various others.

 Marine pollution & eutrophication/hypoxia. See more at: https://en.wikipedia.org/wiki/Marine_pollution

Marine pollution & eutrophication/hypoxia. See more at: https://en.wikipedia.org/wiki/Marine_pollution


One issue that is particularly affecting coastal marine ecosystems is our land-based agricultural actions. Fertilizers from agriculture are carried through the watershed into rivers, and then eventually to the ocean. The phosphates and nitrates in these fertilizers are utilized by photosynthesizers in the ocean the same way they are on land. They inspire and assist growth, and an influx of these molecules in a sunny place (such as the Gulf of Mexico) causes those organisms to explode in number. This is an called algal bloom, and what follows shortly after is the inevitable death of these highly concentrated but short-lived creatures. After dying, they sink to the ocean floor and are broken down by various decomposers. This process uses oxygen; waters with low amounts of oxygen (less than 2 mg/L) are considered “hypoxic” (Vaquer-Sunyer and Duarte 2008).  

Concentrated hypoxia leads to mass die-offs of the marine life on the ocean floor (Diaz 2008). Hypoxic deep water reduces the habitat range for these fish that live in the upper water column. A hypoxic region can even disrupt or halt the migration of marine species because they’re unable to survive traveling through the barren waters (Diaz 2008). An area in which an extreme, consistent hypoxic state exists is referred to as a “dead zone”.

The economic impacts of this issue are widespread and powerful. In the Baltic Sea, estimates show that there would be up to a $10 billion benefit to reducing these hypoxic conditions (Rabotyagov et al. 2014). In North Carolina, the number is estimated to be $1 to 7 million dollars, mostly from the brown shrimp and blue crab fisheries (Rabotyagov et al. 2014). In Chesapeake Bay, annual benefits for the Atlantic flounder fishery would be around 80 million dollars (Rabotyagov et al. 2014). However there are very few studies on the economic affects of hypoxic events or prolonged hypoxic dead zones (Rabotyagov et al. 2014). It’s very specific by region to what species are economically impactful, so detailed and specialized research would need to be done to analyze the economic influence that this process would have in individual fisheries or communities.

Both the Gulf of Mexico and Baltic Sea hypoxic zones have started to develop abatement plans that involve reduction of nutrient loading (Rabotyagov et al. 2014). However, there are difficulties in dealing with non-point pollution and international cooperation for these bodies of water with boundaries that extend through several countries or states. There are also additional questions to be answered such as how temperature affects organisms that live at the bottom, which is also related to the rate of decomposition (Altieri and Gedan 2014). Many questions remain about how hypoxia will interact with other anthropogenic issues, such as ocean acidification.

Sawyer Jenkins is a 4th year UC Davis student who transferred from University of Oregon. His major is Marine and Coastal Science and he looks to have a career in the environmental sector, studying the dynamic relationship between anthropogenic stressors and marine life .

References

Diaz, Robert J., and Rutger Rosenberg. “Spreading Dead Zones and Consequences for Marine Ecosystems.” Science, American Association for the Advancement of Science, 15 Aug. 2008, science.sciencemag.org/content/321/5891/926.

Rabotyagov, et al. “Economics of Dead Zones: Causes, Impacts, Policy Challenges, and a Model of the Gulf of Mexico Hypoxic Zone | Review of Environmental Economics and Policy | Oxford Academic.” OUP Academic, Oxford University Press, 4 Jan. 2014, academic.oup.com/reep/article/8/1/58/1591231.

Vaquer-Sunyer, Raquel. “Thresholds of Hypoxia for Marine Biodiversity.” PNAS, 6 Aug. 2008, www.pnas.org/content/pnas/105/40/15452.full.pdf.

Diaz, Robert, and Rutger Rosenberg. “Marine Benthic Hypoxia: A Review of Its Ecological Effects and the Behavioural Response of Benthic Macrofauna.” ResearchGate, 1995,  www.researchgate.net/publication/236628341_Marine_benthic_hypoxia_A_review_of_its_ecological_effects_and_the_behavioural_response_of_benthic_macrofauna 

Altieri, Andrew H., and Keryn B. Gedan. “Climate Change and Dead Zones.” Freshwater Biology, Wiley/ Blackwell (10.1111), 10 Nov. 2014, onlinelibrary.wiley.com/doi/abs/10.1111/gcb.12754.

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