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Eutrophication, Harmful Algae, Oxygen Depletion, and Acidification

Citation: Brush, M.J., Giani, M., Totti, C., Testa, J.M., Faganeli, J., Ogrinc, N., Kemp, W.M. and Umani, S.F. (2020). Eutrophication, Harmful Algae, Oxygen Depletion, and Acidification. In Coastal Ecosystems in Transition (eds T.C. Malone, A. Malej and J. Faganeli).

Eutrophication is among the most widespread and deleterious anthropogenic impacts to coastal marine ecosystems. The Chesapeake Bay (CB) and Northern Adriatic Sea (NAS) have long histories of nutrient-fueled eutrophication. We compare the susceptibility and symptoms of eutrophication in both systems and discuss recent reversals of eutrophication (oligotrophication) and future considerations. Differences in the residence time of water (CB > NAS), volume relative to the riverine transport of nutrient-rich water (CB << NAS), bathymetry, freshwater-driven seasonal stratification, and density-driven estuarine circulation make CB more susceptible to eutrophication than the NAS. Thus, CB has experienced large accumulations of phytoplankton biomass each spring, widespread summertime bottom oxygen depletion, and long-term loss of submerged aquatic vegetation. Despite its lower susceptibility, the NAS has also exhibited numerous symptoms of eutrophication, including elevated phytoplankton biomass in coastal river plumes, frequent harmful algal events involving a diversity of potentially toxic phytoplankton, unique mucilage events, and episodic oxygen depletion dependent on vertical stratification and current patterns. In recent decades, some of these symptoms have begun to lessen, at least in part due to reductions in nutrient loading. The interaction of oligotrophication with changes in other stressors will become increasingly important, particularly climate-related changes to hydrology, temperature, and acidity.

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The NOAA Ocean Acidification Program (OAP) works to prepare society to adapt to the consequences of ocean acidification and conserve marine ecosystems as acidification occurs. Learn more about the human connections and adaptation strategies from these efforts.

Adaptation approaches fostered by the OAP include:


Using models and research to understand the sensitivity of organisms and ecosystems to ocean acidification to make predictions about the future, allowing communities and industries to prepare


Using these models and predictions as tools to facilitate management strategies that will protect marine resources and communities from future changes


Developing innovative tools to help monitor ocean acidification and mitigate changing ocean chemistry locally


On the Road

Drive fuel-efficient vehicles or choose public transportation. Choose your bike or walk! Don't sit idle for more than 30 seconds. Keep your tires properly inflated.

With your Food Choices

Eat local- this helps cut down on production and transport! Reduce your meat and dairy. Compost to avoid food waste ending up in the landfill

With your Food Choices

Make energy-efficient choices for your appliances and lighting. Heat and cool efficiently! Change your air filters and program your thermostat, seal and insulate your home, and support clean energy sources

By Reducing Coastal Acidification

Reduce your use of fertilizers, Improve sewage treatment and run off, and Protect and restore coastal habitats

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You've taken the first step to learn more about ocean acidification - why not spread this knowledge to your community?

Every community has their unique culture, economy and ecology and what’s at stake from ocean acidification may be different depending on where you live.  As a community member, you can take a larger role in educating the public about ocean acidification. Creating awareness is the first step to taking action.  As communities gain traction, neighboring regions that share marine resources can build larger coalitions to address ocean acidification.  Here are some ideas to get started:

  1. Work with informal educators, such as aquarium outreach programs and local non-profits, to teach the public about ocean acidification. Visit our Education & Outreach page to find the newest tools!
  2. Participate in habitat restoration efforts to restore habitats that help mitigate the effects of coastal acidification
  3. Facilitate conversations with local businesses that might be affected by ocean acidification, building a plan for the future.
  4. Partner with local community efforts to mitigate the driver behind ocean acidification  – excess CO2 – such as community supported agriculture, bike & car shares and other public transportation options.
  5. Contact your regional Coastal Acidification Network (CAN) to learn how OA is affecting your region and more ideas about how you can get involved in your community
       More for Taking Community Action