stormThe marine environment of Casco Bay is changing due to a combination of forces including changing regional climate, ocean acidification, invasive species and coastal development.

The importance and immediacy of coastal change (as we have come to call the confluence of gradual changes affecting our coast) 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.

Green crabs are native to Europe. They were introduced to North America via mid-Atlantic ports perhaps 150 years ago and were first observed in Casco Bay in the early 1900s.  For years, local crab populations were limited by cold winter temperatures.  The exceptionally warm winters of 2012 and 2013 allowed the population to boom, leading to cascading effects on the ecology of Casco Bay.

A cold winter in 2014 appears to have reduced crab populations for now, but it will take years for the Bay to recover.

The marine ecosystems of the future will be different from what we see today, as the ecosystems of today are different from what was present a generation ago. The future will surprise us, as the explosion of green crabs surprised us.


Climate is already changing in the Casco Bay region. In 2009, CBEP commissioned studies on climate change documenting how climate in our area has already changed. Historic records of ice-out in Sebago lake go back more than 200 years. Analysis of that long term record shows that on average, ice out today is about three weeks earlier today than it was 150 years ago.  Portland has nearly one month fewer days with snow on the ground today than in the mid twentieth century.  Temperatures have warmed (both on land, and in the ocean).  Total annual rainfall has gone up, as has intensity of storms.


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 Didemnum, Botryllus and Botrylloides. Many of the non-native species are readily identified with some training.  CBEP is working with the Wells Estuarine Research Reserve to coordinate volunteer-based monitoring for presence of invasive species at several Casco Bay locations.


Resilience is the ability of an ecosystem or a coastal community to recover from disturbance, or more generally, 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.