
How is climate change impacting Casco Bay?
The chemistry of the Bay is changing
Seawater is becoming less alkaline and more acidic.
When carbon dioxide from smokestacks and tailpipes mixes with water, it can make the water more acidic. This is called ocean acidification.
More carbon dioxide ends up in coastal waters as a result of nitrogen pollution from fertilizers, pet wastes, and sewage carried into the sea by rivers, rainwater, and snow melt. This nitrogen overdose stimulates massive algal blooms. When these blooms die and decay, decomposing bacteria consume oxygen and release carbon dioxide in bays and coves. This creates even more acidic conditions for coastal critters. This is called coastal acidification.
Longer and more severe red tides and other harmful algal blooms can be triggered by excess nitrogen and warmer ocean temperatures. Red tides and other harmful algal blooms, exacerbated by nitrogen runoff, may close clam flats to shellfish harvesting for weeks or months and aquaculture operations, affecting jobs and our economy.
Nuisance algal blooms may be the result of the combination of warmer water and excess nitrogen washing off the land. This combination creates ideal growing conditions for thick mats of green algae that can choke our coastal sediments and the creatures that live there.
The water is getting warmer
Water temperature in the Gulf of Maine may rise 2 to 8 degrees Fahrenheit over the next century.

Population shifts are occurring. Harvesters will see more changes in the seafood they catch, as some cold-water-loving species such as cod and lobsters move further north and species such as red hake, turbot, black sea bass, blue crab, butterfish, and summer flounder, move up from mid-Atlantic. We are also seeing more warm-water creatures, such as seahorses and ocean sunfish. ◊
Disruptions in the foundation of the ocean food web already are being observed. Data collected by NASA satellites and researchers at Bigelow Laboratory for Ocean Sciences have found that as water temperature warms, phytoplankton in the Gulf of Maine have declined significantly during the past 20 years.
Phytoplankton constitute the base of the marine food chain. These microscopic plants produce half of the oxygen we breathe! Not only do they nurture all ocean animals (directly or indirectly), but they also absorb carbon dioxide, a by-product of burning fossil fuels, which is the main cause of global warming.

What is Friends of Casco Bay doing to tackle the effects of climate change?
Working at the state level
We helped form and lead the Maine Ocean and Coastal Acidification Partnership to coordinate the work of government agencies, academic institutions, resource harvesters, and nonprofit organizations that are studying ways to reduce the impact of—and help adapt to—the changing chemistry of our ocean
Continuous Monitoring of Casco Bay


Water Reporter
We rely on volunteers to be Water Reporters to report conditions around the Bay, especially areas with nuisance algal blooms, which result in increasing ocean acidification. They use a smartphone app, Water Reporter, to document changing conditions in the Bay through photos taken over time that record the location and date of the observations. We are always looking to grow this network of observers. You can find out more and join here: cascobay.org/water-reporter.
Supporting One Climate Future
Teaching the teachers: Casco Bay Curriculum
- What is an estuary and how has it changed over time?
- How is climate change impacting us locally in Casco Bay and the Gulf of Maine?
Twenty curriculum activities, resource materials, and professional development workshops explain about our estuary and illustrate the regional impact of rising sea level (King Tides), invasive species (Attack of the Green Crab), a changing ecosystem (Winners and Losers Bingo), and how carbon dioxide is a game changer for shellfish and other sea creatures (Acid Ocean).


Baykeeping
What can you do to address climate change?
- While climate change projections may seem daunting, we are fortunate in Maine to have several characteristics that work to our advantage in confronting the challenge. We have a relatively small population, with a large percentage of environmentally-aware citizens. Maine already has a good track record of addressing environmental issues before they become disasters, and our independent, involved voters don’t wait for others to make the first move.
- From measuring your own carbon and nitrogen footprints and making changes in your lifestyle to joining a movement for change in your community, you can be part of the climate change solution.
- Sign up for our emails so you can stay informed about the issues impacting Casco Bay.
- Support our work with a donation.
♦ Jacobson, G.L., I.J. Fernandez, P.A. Mayewski, and C.V. Schmitt (editors), 2009, Maine’s Climate Future: An Initial Assessment. Orono, ME: University of Maine. http://www.climatechange.
◊ Fernandez, I., R. Marvinney, (Editors and Co-Chairs), 2020, Scientific Assessment of Climate Change and its Effects in Maine, Augusta, ME: The Scientific and Technical Subcommittee of the Maine Climate Council. https://www.maine.gov/future/sites/maine.gov.future/files/inline-files/GOPIF_STS_ClimateImpactsMaineReport_Final.pdf