In late October, I took a natural history cruise down the Essex River sponsored by the Great Marsh Symposium.

For the past few years, the group has held daylong conferences where speakers use PowerPoint demonstrations to describe their projects to protect and enhance the Great Marsh.

This year, they decided to hold a series of hands-on field trips instead — a huge improvement in my book. We idled down the river on a beautiful, sun-dappled afternoon as egrets, osprey, cormorants and eider ducks checked us out before flying away.

At the mouth of the river, we landed on the extensive sandspit that juts off the south end of Crane Beach. Unlike most clamflats, the substrate was so sandy we could easily land and walk dry-shod along the shore to a bend in the river. There, an engaging class of students from Boston University showed us where they had planted an acre of life-sustaining eelgrass.

Eelgrass is an angiosperm, a higher-flowering plant similar to what you might find in your garden. In the spring, it produces pollen and tiny underwater yellow blossoms. In the fall, it produces seeds that Indians used to crush up to make flour.

However, unlike other angiosperms, Zostera marina L. was originally a land plant that re-evolved to live back in saltwater estuaries. It is this quirk of evolution that allows two acres of eelgrass to provide over $19,000 a year in environmental services; to provide nursery grounds for food fish, to protect shorelines from erosion, to filter out nitrogen pollution, and release oxygen and detritus that help make estuaries twice as productive as an expensively fertilized field of corn.

But its quirky evolution has also made eelgrass vulnerable to eutrophication from leaky septic tanks. This causes algal blooms to turn the water so turbid that eelgrass can't photosynthesize.

I took off my shoes and waded into the water to investigate the site where the beds of eelgrass were thriving. They were clean and green with only a few tiny sprigs of epiphytic algae growing on their broad blades.

But the water itself was unseasonably warm. This is part of the problem. In 1931, eelgrass up and down the East Coast started to wither and die. The loss of oxygen and rich detritus at the bottom of the food chain set off a devastating domino effect. Populations of fish and shellfish crashed, followed by those of ducks, geese, brant and shorebirds.

Scientists finally blamed this wasting disease on Labyrinthula zosterae, a parasitic slime mold that weakens eelgrass blades and turns them sickly black.

A total disaster was averted when a strand of eelgrass evolved immunity to the disease in Cape Cod’s Pleasant Bay. State and federal officials then replanted most of the East Coast with descendants of the Pleasant Bay eelgrass. But it turns out that the Labyrinthula is temperature sensitive so global warming could hasten a return of this habitat-destroying disease.

Alyssa Novak explained that her students transplanted sprigs of eelgrass from Pleasant Bay along with plants from four other locations that had different temperature and salinity gradients. Their idea was that the plants would hybridize and pick up the traits and immunity they needed to thrive in the Essex River.

It was gratifying to see, but her students had found a new confounding problem. Some of the blades of eelgrass had become so covered with microplastics washing in from the open ocean that they had become less efficient at photosynthesizing oxygen.

Now, every marine biology class has to return home with at least one specimen. In this case, star student Ioanna Karageorge dug up a big, fat, quite delectable soft-shelled clam.

I pointed out that since we were on the Essex River, the Essex shellfish warden would probably come roaring down the river at any moment with a ticket in hand.

Since the sandspit was on Crane Beach, the Ipswich shellfish warden was undoubtedly lurking in the dunes eying her transgressions with field glasses and since the sandspit had grown across the town border that ran down the center of the river in the 1600s, the Gloucester clam cop was probably already launching his patrol boat.

So if she wanted to avoid fines and a huge amount of paperwork, she should probably just hide the succulent bivalve in my food bag for safekeeping. But the teachers had taught their students well and Ioanna was far too clever to fall for any of my Br'er Rabbit ways.

I imagine the clam, nicknamed "Wilson," now sits in a nice well-filtered aquarium in the BU bio department.

Bill Sargent is a North Shore science writer and contributing columnist. His most recent book, "20,000 Years on the Merrimack River," is available in local bookstores and through and


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