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Photo Kaimi Rose Lum
Grad student Brett Thelen goes on regular scouting expeditions for shellfish in East Harbor, aka Pilgrim Lake. |
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Shellfish abound in Pilgrim Lake
Two helpings of seawater a day create veritable wellspring of life
By Kaimi Rose Lum
Banner Staff
TRURO — On the first day, He created widgeongrass. Then came sand eels, flounder and black-spotted sticklebacks. Then tiny grass shrimp. Then anemones. Then acres and acres of glorious shellfish.
Scientists involved in a tidal restoration project at East Harbor, aka Pilgrim Lake, have watched what has unfolded there over the past three years with the same reverence that religious people might apply to the first chapter of Genesis. There is, after all, an element of the miraculous in it — with just two slight helpings of seawater per day, the estuary has bounced back from a weed-choked, midge-haunted, swamp-like water body to a veritable wellspring of life.
The latest thrill is the discovery of a whole new crop of gleaming baby bivalves found two weeks ago by Brett Thelen, a graduate student working for the National Seashore. Last summer, quahogs and steamers were detected in East Harbor, but the more recent find includes razor clams, amethyst gem clams, Baltic “macoma” clams and a fourth species called the false angel wing.
“It’s really neat — just to think that some of the animals we’re seeing no one has seen in this place for possibly 140 years,” Thelen said on Friday after returning from a morning’s worth of sediment sampling in Moon Pond, the southeastern corner of the estuary. “It’s one of those things that, the more you go out, the more you see.”
East Harbor was once connected to Cape Cod Bay by a natural inlet that channeled seawater in and out of the estuary with the change of tide. But the inlet was diked in 1868 so that a railroad could be built across it, and for well over a century the system stagnated. Invasive water weeds took advantage of the brackish environment, algae bloomed and fishkills began occurring on a periodic basis. The low salinity also contributed to outbreaks of midges, pesky black flies that thrived in the harbor sediments.
In 2002, the National Seashore, led by ecologist John Portnoy, got permission from the town of Truro and the state Div. of Marine Fisheries to permanently open the underground culvert that was put in when the highway was constructed in the 1950s. The culvert was engineered to regulate the water level in East Harbor and currently serves as the estuary’s only connection to the bay, a mere drinking straw compared to the wide tidal inlet that once existed there.
But what little seawater is able to flow in through the narrow pipe is having far-ranging effects. Since the tidal restoration began, native saltmarsh grasses have sprung up and a dozen species of estuarine fish and crustaceans have moved in. “You see little winter flounder pretty much every time you take a step in Moon Pond Creek,” said Thelen.
“I think everyone’s really surprised at how quickly plants and animals returned to the area, and without a whole lot of effort on the part of humans.”
Thelen’s focus is on shellfish. She and a small group of volunteers have been venturing out by canoe three days a week for the past few weeks, scooping sediment up from the bottom and running it through a sieve that catches anything bigger than two millimeters. Last week, she brought up over 200 softshell clams from a sediment plot only half a square meter in diameter — “by far we’ve found more steamers than anything else — and blue mussels and periwinkles are another common sight.
The amethyst gem clam (a tiny purplish orange mollusk) and the angel wing (a clam with white, elongated shells) were part of a surprise summer crop that also included a fat type of razor clam known as Tagelus and the Baltic macoma clam.
The shellfish are just young larvae when they make the journey through the long dark culvert into the estuary, Thelen said, somewhat awed. “It’s really astounding. It’s not a huge pipe, so when you think about how so many animals are able to come in through such a small opening, it’s pretty cool.”
Portnoy, the mastermind behind the East Harbor restoration, also reported last week that more bunches of eelgrass had appeared in the estuary and that the widgeongrass, one of the first indicators that the system was returning to health, had really taken off. Another two species of fish, the black-spotted stickleback and the grubby, have been detected recently. And the midge larvae that were once so abundant in the sediments are now contained in one small area in the northwest corner of East Harbor, where the salinity is still relatively low because of the distance from the culvert.
“I think the midge problem has pretty much gone away,” he said.
And Thelen, who will continue sampling for the rest of the summer, said she is enjoying the other wildlife viewing that comes with her field work. A muskrat surfaced near the canoe the other day, and belted kingfishers and green heron are regular sights now.
“It’s so delightful to be out there. It’s such a stark contrast to what it was,” she said.
klum@provincetownbanner.com
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