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How we are moving science forward

Sensor Squad Moves Science Forward

We rely on scientific data on the health of Casco Bay to inform our advocacy and stewardship efforts.

Good decisions are made using good data. That’s the idea behind the Maine Ocean Climate Collaborative.

“The Collaborative is made up of some of the best saltwater scientists in Maine,” says Casco Baykeeper Ivy Frignoca. “By sharing research and knowledge of climate change science, water quality monitoring issues, and ocean climate policies, we can better protect all of our coastal waters.”

Ivy coordinates the Collaborative, which includes Bigelow Laboratory for Ocean Science, Bowdoin College, Casco Bay Estuary Partnership, Downeast Institute, Friends of Casco Bay, Governor’s Office of Policy, Innovation, and the Future, Island Institute, Maine Center for Coastal Fisheries, Maine Department of Environmental Protection, Maine Department of Marine Resources, University of New Hampshire’s Ocean Processes Analysis Laboratory (OPAL), and Wells  National Estuarine Research Reserve (Wells Reserve).

Staff Scientist Mike Doan (left photo) and Science and Advocacy Associate Heather Kenyon (right photo) are working with colleagues up and down Maine’s coast to improve our collective knowledge of how acidification and climate change may be affecting our waters.

A key part of the Collaborative’s current work is to develop a report of recommended equipment, sampling techniques, and quality assurance protocols to serve as a guide for researchers, agencies, and institutions up and down Maine’s coast to better monitor climate change and acidification. For this effort, Friends of Casco Bay Staff Scientist Mike Doan is working closely with colleagues from OPAL and Wells Reserve.

“We call ourselves the ‘Sensor Squad,’” says Mike. “Staff from Wells Reserve and Friends of Casco Bay are testing equipment and protocols in real-world conditions and comparing our data to OPAL’s gold standard. The goal is to ensure we are getting the most accurate climate change and acidification data we can. As the science evolves, we have to evolve, too.”

While the “Sensor Squad” may not look like superheroes, by working together, the scientists are helping improve Maine’s understanding of climate change.

“While our mission is all about Casco Bay, we recognize that climate change doesn’t stop at the watershed’s border,” says Executive Director Will Everitt. “The State of Maine can use our work as a model for what a statewide monitoring program can look like. When state agencies who are tasked with managing and protecting our marine ecosystems have better data, ultimately that helps Casco Bay and all of our coastal waters.”

A Ceremony for Casco Bay and Mother Earth


As more than 115 Friends of the Bay heard at We Are Water — Friends of Casco Bay’s Members Annual Meeting, “olotahkewakon” is the Passamaquoddy word for “ceremony.” Passamaquoddy Language Keeper Dwayne Tomah shared this word in his tribe’s native tongue noting that all of us coming together was a ceremony for our mother earth.

The tribes in Maine were the original stewards of this land and of Casco Bay, beginning more than 12,000 years ago, and today, although there are no official tribal lands on the shores of Casco Bay, Wabanaki people still live within the watershed. Passamaquoddy means “the people who spear pollock.” An important part of Passamaquoddy culture is protecting our air, land, and waters. It is in partnership to those values that we remain honored to have hosted Dwayne, who lives Downeast on Passamaquoddy Bay, as our featured speaker at the event. 

Dwayne’s refrain throughout the evening was “We are all in this together.” The Annual Meeting was attended by local residents, dozens of our volunteers, current and former State Representatives from towns around Casco Bay, federal officials from the Environmental Protection Agency, staff from Maine Department of Environmental Protection, and colleagues from partner organizations, all of whom are working together to improve and protect the health of Casco Bay. As Dwayne said, “We are all in the same canoe, we just didn’t know it.” 

You can listen to Dwayne talk by clicking play on the video below. As caveat, due to the tent we were under and the setting sun, the video quality is low, but we hope you find Dwayne’s talk as inspiring as we did. 

Passamaquoddy Language Keeper Dwayne Tomah

Until recently, Dwayne was the youngest fluent speaker of the Passamaquoddy language. He has dedicated his life to teaching Passamaquoddy language and culture to tribal members. As the Passamaquoddy Language Keeper, Dwayne has been an ambassador, using native words to teach others about his people’s culture while helping us all connect, heal, and learn together. 

His efforts have been vital to keeping the Passamaquoddy language alive. Beginning in the 1600s, European colonizers began taking tribal lands and attempted to extinguish tribal cultures. In the 1800s, Federal policies forced tribes to assimilate into white, christian culture by requiring children be taken from their community and put into boarding schools, among many other egregious acts. Through this process, much of the Passamaquoddy language was lost. 

However, in 1890, the heart of this forced assimilation era, many Passamaquoddy tribal members recorded stories, songs, facts, and conversations on wax cylinders borrowed from Thomas Edison. This was the first field recording of people telling stories and singing ever! 

Although these wax cylinders were owned by the Harvard Peabody museum, they were returned to the tribes in 1980. Dwayne Tomah and others have spent hours meticulously listening to and learning from these recordings, which has resulted in revived energy and pride in Passamaquoddy culture and sovereignty. As one tribal member stated about this project, “it isn’t just language preservation or cultural preservation, it’s people preservation.” Dwayne has been at the heart of this preservation effort.

Frame the Bay

At the Annual Meeting, we announced the winners of “Frame the Bay,” our inaugural photo contest. More than 60 photos were submitted to the contest, which asked Friends to share their favorite photos taken of, near, or on Casco Bay. Participants could submit up to five photos. The judges included internationally recognized sports photographer Kevin Morris, Lindsay Heald, a visual artist, photographer, and producer from Maine, and Board President Sandy Marsters, who has a background in photojournalism.

Scenic Category Winner 1st Place, Student Category Winner, Best of Show wooden posts: Portland Maine, April 2023 by Ava McKinley
Scenic Category 2nd Place Photographer: Timothy R. Brokaw
Scenic Category 3rd Place Photographer: John Bald
Working Waterfront Category Winner 1st Place Photographer: Glenn Michaels
Working Waterfront Category 2nd Place Photographer: Glenn Michaels
Working Waterfront Category 3rd Place Photographer: Adam Mistler
Wildlife Category Winner 1st Place Photographer: Stephen Hobson
Wildlife Category 2nd Place Photographer: Stacey Keefer
Wildlife Category 3rd Place Photographer: Stacey Keefer
Recreation Category Winner 1st Place Photographer: Heidi Holloway
Recreation Category 2nd Place Photographer: Glenn Michaels
Recreation Category 3rd Place Photographer: Bill Brokaw

Our winners in the recreation category were:
First Place: Heidi Holloway
Second Place: Glenn Michaels
Third Place: Bill Brokaw

Our winners in the wildlife category were:
First place: Stephen Hobson
Second Place: Stacey Keefer
Third Place: Stacey Keefer

Our winners in the Working Waterfront category were:
First Place: Glenn Michaels
Second Place: Glenn Michaels
Third place: Adam Mistler

Our winners in the scenic category were:
First place: Ava McKinley
Second Place: Timothy R. Brokaw
Third Place: John Bald

Ava was also our first place student photographer winner and her scenic photo won Best in Show. 

Congratulations to all of our winners!

Casco Bay Award Winner Honorable Jay McCreight

As the State Representative for Harpswell for eight years, Joyce “Jay” McCreight has gone above and beyond for Casco Bay. Executive Director Will Everitt presented her with our Casco Bay Award. As he shared, “Over the course of her legislative career, Jay has been a true Clean Water Hero.” Her achievements include:

  • Passing a bill to set up a process for the disposal of expired marine flares. All seagoing boats are required to have flares in the case of an emergency. These flares expire, remain a fire hazard, and contain toxic chemicals. Until Jay worked on this issue, there has been no safe, ecological, or cost effective way for fishermen and boat owners to dispose of marine flares.
  • Ensuring that the state budget included funds to map eelgrass, a vital habitat known as “the nursery of the sea.”
  • Hosting a forum on water quality in Casco Bay that helped shape recommendations for the Maine Climate Council. 
  • Convening conversations about aquaculture siting.
  • Working hard for fishing families by sponsoring a bill to allow an immediate family member of a lobsterman to fish with their license if the licensee has a serious illness or injury. She introduced this bill after hearing from a lobsterman with cancer who needed his son to keep hauling his traps while he went through treatment.

After eight dauntless years and four rounds of being elected to the statehouse, she was term limited but Jay’s clean water work continues. Jay now serves on Harpswell’s Resiliency and Sustainability Committee and she remains tireless in continuing to help get the flares disposal bill implemented.

Down to Business

Our We Are Water event began with the official business of our Members Annual Meeting. As they looked out at Casco Bay from Spring Point in South Portland, Friends of Casco Bay members unanimously voted Mark Green and Steve Bushey to their second terms on the Board of Directors. We are proud to have their wisdom, experience, and dedication, all in service to our mission to improve and protect the health of the waters we all love. 

31 Years of Seasonal Sampling

Today, on World Ocean Day, we are celebrating our 31st year of collecting seasonal water quality data on the health of Casco Bay!

It also happens to be Casco Baykeeper Ivy Frignoca’s birthday – Happy Birthday, Ivy!

Every year, from May to October, Ivy and Staff Scientist Mike Doan take to our Baykeeper boat and truck to assess water quality at more than 20 locations in Casco Bay. This seasonal sampling includes measuring temperature, dissolved oxygen, pH, total nitrogen, water clarity, salinity, and chlorophyll fluorescence (an estimate of phytoplankton abundance). 

This year, for the first time, seasonal sampling will include testing for PFAS contamination in Casco Bay in collaboration with marine chemist Christoph Aeppli of Bigelow Laboratories for Ocean Sciences. PFAS are a class of widely-used, long-lasting chemicals and are an emerging pollutant of concern in Maine and around the world.

Staff Scientist Mike Doan collects water quality data from our Casco Baykeeper boat, R/V Joseph E. Payne. Mike uses a data sonde – a scientific device that measures water quality characteristics – to measure temperature, salinity, dissolved oxygen, and other parameters.

“There is an important gap in PFAS testing in Maine,” says Ivy. “Current monitoring for contamination in sources like drinking water, fish tissues, and wastewater appropriately focus on public health. However, we don’t know how PFAS pollution is affecting water quality and the environment more broadly, especially in tidal waters like Casco Bay.” 

Our collaboration with Bigelow this summer will help develop a baseline understanding of PFAS levels in Casco Bay, and lay the groundwork for testing in the marine environment moving forward. 

At Friends of Casco Bay, we use all of our seasonal sampling data to help assess the health of the Bay. Mike compares this seasonal work to a regular health check-up. “Like a doctor checking your blood pressure, if we find an anomaly or problem, we can do more thorough investigations,” says Mike. 

Seasonal sampling also enables us to assess water quality over a large area by visiting more than 20 different sites in the Bay. That’s a key difference from our Continuous Monitoring Stations, which collect data at a much higher frequency from three locations in Casco Bay.

Friends of Casco Bay conducts seasonal water quality monitoring at more than 20 locations in Casco Bay, marked by the blue dots. We also gather year-round data at their three Continuous Monitoring Stations, marked by the yellow stars.

The seasonal data we collect this year will add to our historic 30-year dataset, which has become one of the most long-term marine water quality datasets in the United States. Our data show that Casco Bay is warming at the same alarming rate observed in the greater Gulf of Maine. They have helped to designate Casco Bay as a federal No Discharge Area and strengthen legal protections for large areas of the Bay.

We share our data with other scientists as well as with state and federal agencies that use them to meet regulatory mandates. 

“For over three decades, Friends of Casco Bay’s monitoring efforts have provided scientists and regulators a crucial part of the data used to understand the condition of Casco Bay,” says Curtis Bohlen, Director of the Casco Bay Estuary Partnership, one of 28 federal National Estuary Programs. “The next thirty years will see unprecedented change in the Bay. Friends’ monitoring will undoubtedly be at the center of our efforts to witness and understand those changes.”

Willard Beach Reopens to Public

A sewer pipe near Willard Beach burst last week, causing the City of South Portland to temporarily close the beach to the public. We were in contact with the city as they worked to repair the pipe and are grateful for South Portland Water Resource Protection’s quick response to stop the flow into Casco Bay.

The beach reopened on Wednesday night after water quality tests showed it was safe for the public. For more information about the sewer break at Willard Beach, you can follow the City of South Portland on social media or read the media releases on their website

It has been a rough few years for Willard Beach and those who spend their time there. You may remember that in 2021, there was an oil spill and a sewer pipe that burst at the beach.

These incidents are reminders on the importance of investing in our stormwater and sewer systems–and the agencies and departments that maintain them. These investments are expensive and largely fall to municipalities, which often do not have abundant financial resources. Friends of Casco Bay advocates for funds at the state level that help support projects like these. Maintaining stormwater and sewer systems is crucial to keeping our communities healthy and Casco Bay clean. 

We Are Water: Friends of Casco Bay Members Annual Meeting

Wednesday, August 2, 2023, 5:00-7:30 p.m.

Program begins at 6:30 p.m.

Location: Spring Point Field, Southern Maine Community College
50 Lighthouse Circle, South Portland, Maine

Friends of Casco Bay invites you to celebrate the Bay we all love! Join us for delicious hors d’oeuvres, drinks, and the company of Friends who, like you, care about clean water. At the event we will: 

  • Hear Passamaquoddy Language Keeper Dwayne Tomah talk about the importance of working together for cleaner waters and a better world
  • Share a special update on the health of the Bay from Executive Director Will Everitt
  • Announce the winners of the Casco Bay photo contest
  • Celebrate clean water heroes for Casco Bay 

Bring a friend! Let’s connect!

$25 suggested donation is appreciated, not required. Event includes hors d’oeuvres, cash bar.

Directions: From I-295, Take the Forest Avenue South exit (6A). Follow Route 77 (State Street) across the Casco Bay Bridge into South Portland. As you come over the bridge, continue straight. You are on Broadway. Stay on Broadway for approximately 1 mile, until it ends. At the stop sign, turn right onto Pickett Street. At the stop sign, turn left onto Fort Road and take it to the end. Look for Friends of Casco Bay signs.

Thank you to Southern Maine Community College for hosting us.

Announcing: Frame the Bay
The Casco Bay photo contest 

Submissions have closed for Frame the Bay.

Winners in five photo categories – scenic, recreation, wildlife, working waterfront, and student photographer – will be announced at We Are Water! Click here to learn more

Materials for the Annual Meeting portion of the event

2022 Annual Meeting Minutes, Friends of Casco Bay

Friends of Casco Bay 2022 Annual Report to the Community

Board of Directors Elections

New directors are elected by the Board during the year and ratified by the membership at each Members Annual Meeting. Directors serve three-year terms, and they are limited to three consecutive terms. The following board members will be voted on as a slate at the meeting:

For their third three-year term: Board President Sandy Marsters, Sebastian Milardo

Member Survey Results

Dear Friends,

Spring is a time of new beginnings. Ospreys are at their nests. Alewives are swimming upriver. At Friends of Casco Bay, spring means the start of a new fiscal year and the start of Water Quality Monitoring season–in fact, this is our 31st year of collecting data on the health of the Bay!

As we mark these milestones, I want to share our deep appreciation for the many Friends of the Bay who filled out the member survey we sent you last fall. The survey was anonymous, so if you were one of the 400 who responded, thank you for taking the time to share your thoughts.

Casco Baykeeper boat on the water at dawn

Your insights and ideas informed our board and staff as we crafted our new 2023-2028 Strategic Plan and our 2023 Operating Plan. You helped us to recognize where our work is the strongest, as well as identify areas for growth.

It may be no surprise to you that most Friends who took the survey said they consider Casco Bay “home.” The vast majority of you find inspiration and are uplifted by being near the Bay. Whether you are walking trails, visiting islands, or navigating its waters, Casco Bay is a special place to so many of us and supports our emotional well-being.

We were heartened to hear that many Friends think highly of our ScienceBaykeeping, and Community Engagement efforts. We were gratified to learn that we help so many of you understand scientific data about the health of the Bay. We were honored to know that you find us to be a collaborative and trusted organization.

Hundreds of you shared why you value Friends of Casco Bay’s work. Above is a word cloud designed from your answers.

When it comes to the issues we work on most often, Friends who took the survey said they are most concerned about sewage discharges and sewer overflows, oil spills, and climate change. Focusing specifically on the impacts of climate change, we heard that species change and loss, and the changing coastal chemistry of the Bay (like ocean and coastal acidification) are most concerning. All of these issues remain top priorities at Friends of Casco Bay.

In regard to areas of improvement, many of you shared that there should be more opportunities to take action on issues impacting the Bay. In the coming months, we hope to ramp up our community engagement efforts as we now have a full-time staff person dedicated to this work. You also shared ideas for how we can be more inclusive and representative of the community. This goal has become a part of our strategic plan.

Friends of Casco Bay is always learning. We constantly strive to improve our work. Your thoughts and insights help us to do both. Thank you for caring about the health of our waters, and if you ever have suggestions or ideas, please let me k​now.

With appreciation,
Will Everitt
Executive Director

Frame the Bay

Submissions Closed 

Thank you to everyone who submitted photos to Frame the Bay! We hope you will join us at at We Are Water: Friends of Casco Bay’s Members Annual Meeting on Wednesday, August 2 when contest winners will be announced. 

Announcing the Casco Bay Photo Contest

We want to see your favorite photos taken of, near, or on Casco Bay. Show us what the Bay means to you! Winners of the contest will be announced at We Are Water: Friends of Casco Bay’s Members Annual Meeting on Wednesday, August 2.

Photo Categories

Consider this list a source of inspiration. 

  1. Scenic: Send us landscapes, sunsets, lighthouses, and anything that shows the beauty of Casco Bay (underwater photos count, too!). 
  2. Recreation on the Bay. People on boats, walking the shore, swimming, paddling, or otherwise — show us any of the many ways that you see people enjoying Casco Bay. 
  3. Wildlife and Animals. Dogs, birds, sea creatures…you name it! We want to see the critters of the Bay.
  4. Working Waterfront. Submit a photo of lobstermen on their iconic boats, workers on the wharves and vessels that define our harbors, or any image that shows how Casco Bay relates to our local economy.
  5. Student Photographer. Are you 18 or younger? If so, tell us when you submit your photos.

All photos will be considered general submissions and our judges will choose winning photos for each category. We will have a great set of prizes for the winners.

Submission Guidelines

  • Each person can submit a maximum of five photos
  • Photos must be taken in Casco Bay or the Casco Bay watershed
  • Photos must be taken between 2020 and the present day. 

How to Submit Photos

  • Send photos via email to friends@cascobay.org. Submissions close on Wednesday, July 5 at 11:59 p.m.
  • High resolution photos are preferred (if prompted, select “original size” when sending your photos).
  • Your subject line should read “Frame the Bay”
  • Please include in your email:
    • the location and year your photo was taken
    • your name
    • if you are under 18 (so you can be considered for the Student Photographer category)


Thank you to our judges: Kevin Morris, Lindsay Heald, and Sandy Marsters.  

Unless you tell us otherwise, Friends of Casco Bay may use any photo submitted to the contest in future communications such as our website, newsletter, and emails. If and when we do, we will gladly credit you as the person who took an amazing photo!

Water as Inspiration: Art and Casco Bay

What are the connections between creativity, the environment, and climate change? How can art convey powerful ideas when words fail us?

At Water as Inspiration: Art and Casco Bay, Staff Writer Robby Lewis-Nash sat down with three regional artists – Anna Dibble, Mitchell Rasor, and Jan Piribeck – for a discussion about water, the environment, and art. Above is a full recording of the event for those of you who were not able to attend or want to revisit the conversation.

If you don’t have time to watch the full recording, here are a few key moments you may want to check out:

In this 20 minute clip, Anna, Mitchell, and Jan all show images of their work and share what inspires them to create (hint: in one way or another, it all comes back to the Bay!).



In this 4 minute clip, our panelists describe the role of art and artists in addressing environmental issues like climate change.

“Secrets of the past” – Malaga Island and Casco Bay

Most Friends of the Bay can agree with the words, “I love Casco Bay.” In one way or another, the Bay is an important and special place to many of us. It is a place we feel we belong, a place we call home. 

We know from history that some who have called the Bay home, even for decades or generations, have not been treated with respect, dignity, or basic humanity. Knowing this history can help us understand where we are now and where we want to go. 

One of these stories is of Malaga Island and the people who lived there.

John and Rosella Eason, with unidentified children, stand in front of their home on Malaga Island on July 20, 1911. John Eason was a carpenter and mason, and well-known for his occasional sermons when bad weather prevented island residents from attending church. Photo credit: Collections of the Maine State Museum (96.38.189)

Malaga is one of hundreds of islands in Casco Bay. It lies in the waters just off of the coast of Phippsburg near the mouth of the New Meadows River. Its 42 acres host rocky shores and a dense evergreen forest, like so much of coastal Maine. 

If you were to visit Malaga a little more than a century ago, you would have met the people of a small, mixed-race fishing community. Historians say that many of the island’s residents could trace their ancestry to Benjamin Darling, a black man who owned and lived on Harbor Island, just a half-mile south of Malaga. 

In the 1860s, some of Darling’s descendants and others settled on Malaga Island. At the time, islands in Maine were challenging to access and difficult places to live. For the most part, no one would mind if a group of people settled down on an uninhabited island like Malaga. 

By the turn of the century, Malaga was home to many families and had a population of just under fifty people. Life on the island would have been similar to that of other small fishing communities in Maine. While fishing provided income and sustenance for many, there was other activity on the island, too.

A red schoolhouse was built on Malaga in 1909. Some thought that the education there was better than on the mainland, and at least one student from Phippsburg paid tuition to attend the school. Photo credit: Collections of the Maine State Museum (96.38.178)

Children attended school at the home of islander James McKenney. When a schoolhouse was built in 1909, some said the education there was better than on the mainland. There was religious life as well, where community members would attend church in Phippsburg. When bad weather prevented travel, carpenter and mason John Eason would preach, earning him the nickname “the deacon.” Another industrious resident named Eliza Griffin worked on and off the island doing laundry, housekeeping, and fishing. She was said to have more income than any man on Malaga. 

While the community on Malaga was established and growing, other forces in Maine were shifting that would eventually lead to the eviction of all residents.

In the early 1900s, racism and growing belief in eugenics were widespread. Newspapers began reporting sensational and dehumanizing stories focused on Malaga, describing the community as immoral, disgusting, and a stain on Casco Bay. Economic downturn was also at play. The decline of shipbuilding and other industries had towns like Phippsburg and the State of Maine focused on developing tourism, which was thought to be incompatible with the presence of a working class, mixed-race fishing community. 

Ownership of Malaga Island, rising social tensions, and political retribution are among the other factors that may have contributed to the state’s eviction order, demanding all residents leave the island by July 1, 1912. Some residents resettled on the mainland or other islands. No homes were provided for the families, and many dismantled their houses and carried them away to rebuild elsewhere.

Eight Malaga residents, including the Marks family, were forcibly institutionalized at the Maine School for the Feeble-Minded (today, Pineland Farms). The group was separated by sex upon their arrival and many of them died there in the years immediately following. The School is also the resting place of those who lived and died on Malaga, as the State of Maine removed and reburied all remains from the Island’s cemetery.

Since 2001, Malaga Island has been a Maine Coast Heritage Trust (MCHT) public preserve. A longtime practice of local lobstermen storing traps and gear on the island continues to this day under MCHT management. You can visit the MCHT website to learn more about how to visit Malaga Island. Photo credit: Andrew Deci, MCHT

For generations after the eviction, many descendants of the Malaga Island community hid their ancestry. The slur, “Malagite,” continued to be used throughout Maine. 

More recently these sentiments have shifted. Today, more people know the story of Malaga Island. Hundreds of Mainers across the state can trace their ancestry back to the island’s community, and for some it is no longer a source of shame, but one of pride.  

Marnie Childress is a descendant of Benjamin Darling and grew up in South Portland. Marnie was often on the water as a child. It wasn’t unusual for her father to take her clamming in the early morning before school. For Marnie, being on the water near Malaga today is a way to connect to her heritage, even alongside its painful history. 

“All the islands of Casco Bay have their secrets of the past,” says Marnie. “When I am on a boat around Malaga, it’s like being on the water with my dad again. I just feel the history there, and it makes me love it even more.” 

We hope that by sharing the story of Malaga Island today, when racism and prejudice continue to affect communities that surround Casco Bay, more of us will learn that racism does have roots in this region. 

We believe that the health of Casco Bay is tied to the health of the communities that surround it. A healthy Casco Bay is one where anyone is welcome, one where we can all belong and call this place home. 

To learn more about Malaga Island and its history, you can follow the links below. 

Malaga Island: A Story Best Left Untold, radio story by Rob Rosenthal & Kate Philbrick

Explore Malaga Island – Educational Materials, Maine State Museum

Malaga Island: An Overview of its Cultural and Natural History, Maine Coast Heritage Trust

Continuous Monitoring Station Data Show Warm Winter

If you were to swim in Casco Bay on a winter day, you would probably be thinking one thing: cold! 

But for marine life, it’s a different story. Especially this winter.  

Data from our Yarmouth Continuous Monitoring Station show Casco Bay is about 4°F warmer than the past seven winters, on average. This observation comes as scientists continue to report year-round temperatures in Casco Bay and the Gulf of Maine are rising faster than most other water bodies on the planet.

Winter water temperatures in 2023 are some of the highest we have seen since we began continuous data collection in 2016. This graph compares 2023 daily mean temperatures (the blue line) to the past seven years of temperature data (the gray line and shaded area) from our Yarmouth Continuous Monitoring Station. You can view all the data from our stations yourself on our website.

“While four degrees may not seem like much, this seemingly small change in temperature can kick off a cascade of changes throughout Casco Bay’s ecosystem,” says Staff Scientist Mike Doan. Green crabs provide a compelling example.

Originally from Europe, green crabs are estimated to have arrived in Maine around 1900 after hitching a ride on ships crossing the Atlantic Ocean. Their preference for feeding on shellfish like softshell clams became a clear problem in the 1950s, when an increase in water temperatures coincided with a boom in Maine’s green crab population. Softshell clam harvests plunged in those years. The fishery rebounded after colder water temperatures returned in the 1960s and the green crab population declined.

The connection between warmer water temperatures and more green crabs has been seen repeatedly in Maine. Scientists think this is partly because green crabs struggle to survive colder winters, but fare much better when water temperatures warm.

Despite their name, green crabs are not distinctly green! The top of their shell can range between dark brown and green, with flecks of yellow. The bottom of their shell can be white, orange or red. Photo: Jessica Batchelder

Green crab populations have surged many times in recent decades, often with devastating consequences for softshell clams and the Mainers who harvest them. In addition to predating on clams, green crabs also pose a threat to one of the most important lifeforms in Casco Bay: eelgrass.

Eelgrass is an ecologically vital, ribbon-like seagrass that grows underwater in the shallows of Casco Bay and Maine’s coast. Eelgrass meadows provide nursery habitat for many kinds of fish and shellfish, and help maintain water quality by absorbing nutrients and stabilizing sediments. Eelgrass meadows also help address climate change, as they are exceptionally good at absorbing and storing carbon dioxide.

When a green crab encounters eelgrass as it scuttles along the bottom of the Bay, it will often clip the grass at the base and continue to search the area for food. Juvenile crabs may feed on the base of the plant itself. This behavior is thought to be a major cause of eelgrass loss, where a 2012 – 2013 boom in green crab populations coincided with the loss of nearly fifty percent of the eelgrass in Casco Bay.

As we think about this winter’s warm water temperatures, green crabs, and their potential impacts, it is important to remember a common saying that any scientist will know: correlation does not imply causation. In a complex ecosystem like Casco Bay, there are many factors that influence the size of green crab populations. Temperature is only one of them.

“It would be misleading to say that we will certainly see more green crabs in the Bay this summer,” says Mike. “But with what we know from science and Maine’s history, it’s fair to say there is a good chance we will see more green crabs in the coming months.”