Crabs may be killing Cape Cod’s marshes
By Carolyn Y. Johnson
Boston Globe Staff / July 6, 2010
HARWICH — For the past seven years, scientists have been alarmed by the mysterious death of marsh grasses on Cape Cod, which is transforming expanses of lush green wetlands into lumpy mudflats with the appearance of Swiss cheese.
Tweet 1 person Tweeted thisSubmit to DiggdiggsdiggYahoo! Buzz ShareThis Work over the past few years has provided strong evidence that the marshes are being eaten away by a particular crab, called Sesarma reticulatum, whose appetite for cordgrass is leaving marshes vulnerable to erosion. The work is also revealing the possibility that human disturbances may have set off the chain of events that caused the crabs’ hungry assault, in turn endangering some of the world’s most important ecosystems.
“One of the pretty scary things is the leading edge of these marshes is the front-line defense for sea-level rise,’’ said Mark Bertness, a biology professor at Brown University who has been working intensively to under stand so-called die-off on the Cape for three years. “They are hurricane buffers and nursery grounds to all kinds of shellfish and finfish, and buffers from run-off — an important filtering system.’’
This summer, Bertness and colleagues are monitoring 14 marsh sites — some dead or dying — to unravel the complicated chain of events that is unfolding.
Early findings suggest that predators of the Sesarma — blue crabs, striped bass, or fish called tautog — are less prevalent in marshes disturbed by human activity, including fishing. To Bertness, that suggests recreational fishing has reached a “tipping point,’’ altering nature’s balance by depleting the crab’s enemies and thus allowing them to thrive in greater number.
“This lumpy area — it would have been all grass a few years ago,’’ said Andrew Altieri, a postdoctoral researcher at Brown University, as he stood on the edge of Saquatucket Harbor one recent morning. He held up one of the purple-tinged, 2-inch-long nocturnal Sesarma crabs between his fingers.
“It’s obvious now, the crab is eating the marsh — essentially clear-cutting the vegetation,’’ Altieri said. “There are some marshes that are just wasted.’’
While many scientists agree the crabs are playing an important role in the die-off in the marsh, it is still an open question why the crab chowdown has suddenly become a problem, and how to combat it. Marsh health is complicated, affected by rainfall and run-off, the plant and animal life within it, and other factors that make simple explanations elusive.
Stephen Smith, a plant ecologist at the Cape Cod National Seashore, spent last summer engaged in the Sisyphean task of attempting to rid an area of the crabs. Now, he is experimenting with biodegradable netting that might be able to control erosion and keep the crabs out of an area to allow marsh to recover.
“It’s looking like a classic story of humans altering one link in a food chain and everything going nutty, having cascade effects
By Carolyn Y. Johnson
Boston Globe Staff / July 6, 2010
HARWICH — For the past seven years, scientists have been alarmed by the mysterious death of marsh grasses on Cape Cod, which is transforming expanses of lush green wetlands into lumpy mudflats with the appearance of Swiss cheese.
Tweet 1 person Tweeted thisSubmit to DiggdiggsdiggYahoo! Buzz ShareThis Work over the past few years has provided strong evidence that the marshes are being eaten away by a particular crab, called Sesarma reticulatum, whose appetite for cordgrass is leaving marshes vulnerable to erosion. The work is also revealing the possibility that human disturbances may have set off the chain of events that caused the crabs’ hungry assault, in turn endangering some of the world’s most important ecosystems.
“One of the pretty scary things is the leading edge of these marshes is the front-line defense for sea-level rise,’’ said Mark Bertness, a biology professor at Brown University who has been working intensively to under stand so-called die-off on the Cape for three years. “They are hurricane buffers and nursery grounds to all kinds of shellfish and finfish, and buffers from run-off — an important filtering system.’’
This summer, Bertness and colleagues are monitoring 14 marsh sites — some dead or dying — to unravel the complicated chain of events that is unfolding.
Early findings suggest that predators of the Sesarma — blue crabs, striped bass, or fish called tautog — are less prevalent in marshes disturbed by human activity, including fishing. To Bertness, that suggests recreational fishing has reached a “tipping point,’’ altering nature’s balance by depleting the crab’s enemies and thus allowing them to thrive in greater number.
“This lumpy area — it would have been all grass a few years ago,’’ said Andrew Altieri, a postdoctoral researcher at Brown University, as he stood on the edge of Saquatucket Harbor one recent morning. He held up one of the purple-tinged, 2-inch-long nocturnal Sesarma crabs between his fingers.
“It’s obvious now, the crab is eating the marsh — essentially clear-cutting the vegetation,’’ Altieri said. “There are some marshes that are just wasted.’’
While many scientists agree the crabs are playing an important role in the die-off in the marsh, it is still an open question why the crab chowdown has suddenly become a problem, and how to combat it. Marsh health is complicated, affected by rainfall and run-off, the plant and animal life within it, and other factors that make simple explanations elusive.
Stephen Smith, a plant ecologist at the Cape Cod National Seashore, spent last summer engaged in the Sisyphean task of attempting to rid an area of the crabs. Now, he is experimenting with biodegradable netting that might be able to control erosion and keep the crabs out of an area to allow marsh to recover.
“It’s looking like a classic story of humans altering one link in a food chain and everything going nutty, having cascade effects