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Ocean Acidification: A Growing Concern in the Gulf of Maine

May 28, 2014
Spring 2014

When carbon dioxide dissolves into seawater, it forms carbonic acid that lowers the waters pH, making the more acidic--this is ocean acidification. While scientists are still far from understanding the full ecological effects of ocean acidification, it is clear that it affects the Gulf of Maine's ecological and economic health. In response, scientists, local and state resource managers, and shellfish growers from across the region, are coordinating efforts to address critical science gaps.

What scientists do know is that ocean acidification is a global problem and its impacts, though not immediate, will be felt for thousands of years. The ocean absorbs much of the extra carbon dioxide released by burning fossil fuels.

On a smaller scale, local drivers such as deep ocean upwelling (as seen on the West Coast) and acidic freshwater discharge from rivers and streams can contribute to coastal acidification. Freshwater is typically more acidic than seawater but in addition to its relative acidity, freshwater discharge also contains dissolved organic compounds and nutrients from fertilizers and other land-based sources that affect the pH balance in nearshore waters. For states like Maine, where the occurrence of pH fluctuations in coastal areas poses immediate concerns for shellfish, local acidification events have been linked to juvenile clam and larval oyster die-offs.

These localized acidification events can offer a glimpse into how ocean acidification will affect the Gulf of Maine as a whole as pH levels continue to drop. In 2007, a team of scientists led by Woods Hole Oceanographic Institute, conducted the first comprehensive seawater inorganic carbon chemistry survey of the East Coast. Leading up to this study, scientists knew very little about ocean acidification along the eastern seaboard; many were surprised by the studys findings that the Gulf of Maine Gulf of Maine is uniquely vulnerable to acidification.

Researchers point to two main factors that contribute to the Gulf's vulnerability: cold, fresher water from the Labrador Current, and the high volume of fresh water from rivers and streams flowing into the Gulf. These variables increase the Gulf of Maine's sensitivity to ocean acidification because cold, fresh water more readily absorbs carbon dioxide, leading to faster rates of acidification. In addition, precipitation and freshwater discharge into the coastal ocean are predicted to increase in the future.

Remarkably little is known about the effects of ocean acidification on marine ecosystems. For shell-forming mollusks like clams, oysters, mussels, and scallops, changes in pH and carbonate chemistry can interfere with their ability to build and maintain their calcium carbonate shells. Lab studies show that increased levels of acidity in seawater, can lead to slower growth and development, deformed shells, and higher rates of mortality. The planktonic larval stages of many species are also vulnerable, a concern for hatcheries and wild populations of shellfish, which rely on good survival of larval stages to replenish loss of adults. Meanwhile, the impact of acidification on crustaceans, which include lobsters and crabs, is less clear. Currently there are only two published studies on the effects of acidification on American lobster and they present conflicting results.

Efforts on both coasts are underway to build a better scientific understanding of the present and future effects of ocean acidification on coastal ecosystems. In Washington and Oregon, where the shellfish industry is valued at $272 million, scientists, fishermen, and shellfish growers have developed innovative business-science partnerships to track the effects of ocean acidification at shellfish hatcheries. Monitoring equipment installed at shellfish hatcheries give managers the ability to predict and respond to possible threats related to acidification, and provides scientists with much needed data. Similar efforts are also underway in California and Alaska.

On the East Coast, several regional outreach and monitoring initiatives are in development. In New England, an interdisciplinary group named the Northeast Coastal Ocean Acidification Network (NE-CAN) brings together scientists, federal and state agency representatives, resource managers, and seafood industry representatives to coordinate outreach, research, and monitoring efforts across the region. Similarly, in the Mid-Atlantic, scientists and stakeholder groups are working to design an acidification monitoring network for the Chesapeake Bay.

Meanwhile, individual states on both coasts are taking legislative action to study and address the potential impacts of ocean acidification. In 2012, Washington created its Blue Ribbon Panel on Ocean Acidification, the countrys first comprehensive ocean acidification initiative. More recently, Maine became the first East Coast state to pass an ocean acidification bill into law. The law will establish a committee comprised of fishermen, scientists, and shellfish growers to investigate the effects of ocean acidification on the marine ecosystem.

Ocean acidification is a global problem and an emerging concern for the Gulf of Maine. Economically, the potential impacts are staggering for a region where a majority of the commercial fisheries and aquaculture industries by volume and value are reliant on shell-producing species. In 2011, American lobster and sea scallops comprised 70% of the regions commercial fisheries revenue; however, the effects of ocean acidification on both of these organisms are, surprisingly, still largely unknown.

With so many unknowns and so much at stake, the need for better science through monitoring, research, and stakeholder outreach is crucial and immediate. Improving our understanding of the impacts of ocean acidification on the Gulf of Maine now is a critical step toward ensuring the ecological and economic health of the Gulf in the future.