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Friends’ Volunteers Document Eelgrass Mystery

Volunteer Water Reporters and Friends of Casco Bay staff visited two Brunswick salt marshes in early September, where they shared observational insights and discussed local ecology.


Water Reporter Heather Osterfeld’s post from September 8 shows torn and uprooted eelgrass in Maquoit Bay. Water Reporters have noticed an increase of eelgrass adrift in the Bay since mid-August – from Brunswick west to Freeport, Yarmouth, Cumberland, and Falmouth.

Water Reporters up and down Casco Bay have been documenting an increase of torn and uprooted eelgrass washing ashore from mid-August through September. Falmouth Town Landing, Broad Cove, Wolfe’s Neck, and Maquoit Bay are among the locations where Water Reporters have encountered piles of this ecologically vital, ribbon-like seagrass.

Eelgrass (Zostera marina) grows underwater in the shallows of Casco Bay. Eelgrass meadows are recognized as critical nursery habitat for economically important fish and shellfish. Eelgrass helps to maintain water quality by absorbing nutrients and stabilizing sediments. These seagrass beds can also help the Bay be more resilient to climate change, serving as natural carbon sinks by absorbing carbon dioxide during photosynthesis and making our coastal waters less acidic.

In recent years, some eelgrass beds in Casco Bay have been decimated by rising populations of invasive green crabs. Scuttling through an eelgrass meadow along the bottom of the Bay, adult green crabs clip and uproot eelgrass as they search through bottom sediments for prey, while juvenile crabs may feed on the base of the plant itself. A particularly extreme example of this dynamic occurred between 2012 – 2013, when a boom in the green crab population coincided with the loss of nearly fifty percent of the eelgrass in Casco Bay.

When Casco Baykeeper Ivy Frignoca and Water Reporters take a closer look at the eelgrass that is washing ashore today, they often notice fraying at the stems indicative of green crab mandibles and claws. However, not all of the eelgrass displays this fraying, and Ivy and others speculate that the quantities of dead eelgrass are too large to be caused by green crabs alone.

“We are not sure why we are seeing so much eelgrass washing ashore,” said Ivy. “We have asked state officials to look into this and they are. Continuing to have Water Reporters track where and when eelgrass is coming ashore is key to figuring out what factors may be causing the problem.”

Sometimes being stewards of the Bay means following the clues just as Sherlock Holmes might.

Identifying the difference between the frayed stems of eelgrass clipped by green crabs from eelgrass that has been uprooted by a passing boat or other activity can require a discerning eye. The same kind of observational nuance applies to assessing the potential source of an algal bloom, or hypothesizing which factors are causing a specific stretch of salt marsh to erode. Ivy and Friends’ Community Engagement Coordinator Sarah Lyman met up with Water Reporters in early September, to hone observational skills while discussing questions and sharing insights.

“Many Water Reporters have an intimate familiarity with specific parts of the Bay. When we come together to share our knowledge and perspectives, we all leave knowing more about each other and the Bay,” said Sarah. “That’s what I love about Water Reporter: these folks that care about this place are learning alongside us and teaching us at the same time.”

Sarah and Ivy will be organizing more meetups for Water Reporters around the Bay in the coming months. To stay up to date on Water Reporter events and help us keep an eye on changing conditions in Casco Bay, join us.