What is OA?

What are ocean and coastal acidification?

Ocean acidification is a change in ocean chemistry caused by seawater absorbing excess carbon dioxide (CO₂) from the atmosphere. CO₂ is an “acid gas”: when it dissolves in water, it becomes carbonic acid. The more CO₂ the ocean absorbs, the greater its acidity and the lower its pH (the scale scientists use to measure acidity). The ocean absorbs about ¼ of the CO₂ attributed to human activities in the atmosphere every year, meaning as carbon emissions rise so will the acidity of the ocean. Ocean acidification occurs worldwide and will likely have significant effects on ocean life as well as marine economies and industries.

Coastal waters are also acidified by CO₂ generated as a consequence of nutrient runoff caused by human activities (e.g., nitrogen and organic carbon from fertilizers and development), leading to algal blooms and low oxygen events (hypoxia). Freshwater rivers, melting glaciers, and pollutants can also increase acidification in coastal areas.

Why is it important to understand ocean and coastal acidification?

Scientists have recently discovered that many ocean species are sensitive to the changes in ocean chemistry caused by ocean and coastal acidification. Many species, especially those that produce hard shells or skeletons, respond negatively to acidified ocean conditions in the laboratory. For example, some coral and zooplankton, including the early life forms of species like crab and oysters, have difficulty growing and maintaining their shells or skeletons and experience reduced survival. Scientists have already observed poor shell condition in pteropods, also known as sea butterflies, collected from the wild and linked this observation to acidified ocean conditions. Such impacts and others on species as diverse as fish and algae raise serious concerns for how marine ecosystems and the human communities that depend on them may be affected by ocean and coastal acidification. Aquaculturists have also observed the effects of ocean and coastal acidification on their industry, and have taken steps to mitigate acidification’s negative impacts of oyster hatcheries and to explore its positive impacts on macroalgae such as kelp and edible seaweeds.

How will human communities be affected by ocean and coastal acidification?

Ocean and coastal acidification will likely impact human livelihoods, especially in those communities whose culture and economy are defined by the sea and its resources. Fisheries, a major food industry globally, depend on healthy fish and shellfish populations and may be at risk if ocean acidification alters them. The impacts of acidification on marine species could be especially alarming for Tribal communities that rely on the seas for physical, cultural, and spiritual sustenance. Efforts are underway to identify how to prevent, mitigate, and adapt to ocean acidification in order to protect and preserve marine resources and the health of the communities that depend on them.