The marine environment of Casco Bay is changing due to a combination of forces, including a changing regional climate, ocean acidification, invasive species and coastal development. Resiliency is the ability of the natural and human environment to absorb and recover from the changing climate, including increased severe storms, sea level rise, and resulting changes such as ocean acidification and increased invasive species. Social and economic resilience is closely tied to environmental resilience.

Climate Change

Long-term data on conditions over the past century reveal clear trends in Casco Bay’s climate, trends that are expected to continue. Climate models for the watershed show further summer temperature increases of 2 to 6 degrees F by mid-century and by the end of the century, climate scientists expect that Portland will have 15-30 fewer winter days with temperatures below 32 degrees F. Sebago Lake’s ice-out in the spring occurs 23 days earlier than it did in 1807. Between 2004 and 2013, the Gulf of Maine warmed at a rate of .41 degrees F per year – faster than 99 percent of the world’s ocean.

Maine is experiencing increases in both total annual precipitation and extreme precipitation events. Intense rain events typically occurred about once a year in the 1940s but are now occurring in Portland about three time a year. And the number of extreme precipitation events – categorized as coastal floods, flash floods, floods, heavy rain, and tropical storms – has increased dramatically.

In the past two decades, sea level rise increased 130 percent faster than the average rate in the last 100 years. Studies indicate that sea level could rise another 2 to 10 feet by 2100.

And the ocean is acidifying at a rate at least 100 times faster than at any other time in the past 200,000 years. Approximately one quarter of human emissions of C02 is being absorbed by the ocean, causing seawater to become more acidic.

Invasive Species

A 2013 regional study searched for non-native marine species at two Casco Bay sites, one in Freeport and the other in South Portland.  At each site, one fifth of the species encountered were non-native, while another one fifth are of uncertain origins (may be native or non-native).  Non-native marine species included a wide range of different taxa, including algae, skeleton shrimp, two species of crabs and european oysters.  Among the most widespread non-native species in our area are the periwinkle, the green crab and several encrusting colonial tunicates, including DidemnumBotryllus and Botrylloides.

The importance and immediacy of coastal change has been highlighted over the last few years by a population explosion of green crabs.  Burgeoning crab populations decimated local clams, triggered a loss of nearly two thirds of the eelgrass beds in the Bay and had significant negative effects on coastal fisheries like the soft-shell clam harvest.

Shoring Up Our Communities for Coastal Change

Resilience is the ability of an ecosystem or a coastal community to remain healthy and vibrant in the face of external pressures like climate change.  Resilient coastal ecosystems are less likely to collapse in the face of change and are more likely to continue to provide environmental goods and services despite external pressures.  Protecting and enhancing resilience of coastal ecosystems and coastal economies are important policy goals in an era of coastal change.

Current Projects

Tidal restoration into salt marshes. In recent years, CBEP staff have led or partnered on several tidal restoration projects in Casco Bay’s salt marshes.  Projects such as the Thomas Bay Marsh restoration project at Adams Road in Brunswick, in which an undersized and corroded culvert was replaced with a larger aluminum pipe arch, have enhanced the Bay’s salt marshes by providing more frequent and extensive tidal inundation into upstream wetlands, delivering salt and sediments to areas and in the process, enhancing system resilience to stressors such as sea level rise.

Living shorelines pilot project. Through a collaborative project with the Maine Coastal Program at DMR, the Maine Geological Survey, The Nature Conservancy, Maine Coast Heritage Trust, and local municipalities, four ‘living shoreline’ demonstration sites will be constructed at sites around the Bay in the spring of 2019.  Where suitable, living shorelines, which are typically constructed of natural materials such as wood, rocks, shell, and plants, can be utilized to stabilize eroding coastal banks while providing ecosystem benefits. Unlike hard shorelines like seawalls or rip-rap, which impede the growth of plants and animals, living shorelines are intended to grow over time.  CBEP staff will be monitoring these demonstration sites to evaluate their effectiveness and provide data to state and federal regulators in the hope that their use will expand in Maine.

Volunteer-Based Marine Invasive Species Monitoring (MIMIC) – We support our partner Wells Estuarine Research Reserve in coordinating volunteer-based monitoring for presence of invasive species at several Casco Bay locations.

For More Information

Read our Climate Change Summary Report (2017) here and our Climate Change Fact Sheet here. Check out our Resources page for many other documents and reports.

Contact CBEP at (207) 780-4820 or