An army of green crabs waits under icy waters from the Great Marsh to Plum Island Sound.

The crabs wait for spring and warmer temperatures. When they emerge they will devour the foundation of Ipswich’s largest industry, the soft shell clam. They will eat a key to the Great Salt Marsh, eel grass. They will erode tidal riverbanks.

From restaurant menus and the clamming industry to the Great Salt Marsh’s environmental and economic resources, the palm-sized green crab is attacking the region’s identity.

The seemingly insatiable, indestructible benthic scavenger lives in sheltered areas like salt marshes and intertidal zones, reproduces in massive numbers and, most importantly and most devastatingly, eats soft shell clams.

As the ravenous, invasive species proliferates, so does the green crab resistance movement that includes clammers, trappers, researchers, constables, chefs and senators. Their goal is simple: Save the clams and preserve the Great Marsh. Their strategy is equally simple: Kill as many green crabs as possible as quickly as possible.

Trapping the green crab seems to be the main way to control the population, so far, and Ipswich just received a $15,000 state grant on Tuesday, Feb. 2, to continue its trapping program in 2016.

Impact on clamming

Green crabs’ appetite for Ipswich’s main export, the soft shell clam — a $6 million-a-year industry in Ipswich — worries experts.

Jeff Kennedy said that N4 and N7, the clamming areas that include Essex Bay and the Plum Island Sound, consistently represent about half of soft shell clam landings statewide. Massachusetts clammers landed 6.2 million pounds of soft shell clams in 2007. In 2014, that number dropped to just over 2 million pounds.

Kennedy is the Massachusetts Shellfish Sanitation and Management program's Regional Shellfish Supervisor.

Though Kennedy noted that industry shifts can’t be attributed to the green crab alone, many experts believe the green crab represents one of the most serious threats to the clamming industry.

Ipswich Shellfish Constable Scott LaPreste said that wherever seeded clam beds are found, the green crab is present in massive numbers.

The soft shell clam cost per pound reflects the lowered supply, jumping from $1.35 in 2007 to $2.13 in 2015.

A higher price for soft shell clams isn’t the only effect on seafood lovers. Food writer Heather Atwood said that as the price for soft shell clams rises, many restaurants are turning to sea clams to meet the fried clam demand. Unwitting restaurant-goers expecting soft shells are often served an entirely different species.

“They’re these huge clams,” Atwood said. “One clam can weigh half a pound. They cut them into strips and fry them. People aren’t realizing this. Those are not the same thing as soft shell clams. Clams with bellies are the true soft shell clams.”

Turner’s Seafood owner Joe Turner acknowledged that many people are fooled into thinking that the sea clam strips they order at some restaurants are soft shell clams. “A lot of people’s understanding is that it is a regular fried clam without the belly,” Turner said. “We would never sell a clam strip off disguised as a frying clam, but I can see why restaurants would do it and change the offering on the menu.”

Atwood worries that unless there is significant investment in curbing the green crab population, soft shell clams will disappear from menus. “We have to do something about this or they will be gone forever,” Atwood said. “Going to clam strips is the easy way out. They just want to stay in business and not let anyone know that they are using sea clams. I think if people knew that, these clam places would be hurting. I’ve been beating the green crab drum ever since I heard about this.”

Trapping

As the effects of the green crab became more apparent, Ipswich rallied against the predator, creating the area’s first green crab bounty program in 2014.

“Our clamming industry is a multimillion dollar industry,” LaPreste said. “Ipswich in one year landed one third of the entire soft shell clam total poundage for the whole state. It’s a big industry here and it’s worth a lot of money and the town understands that. We have a good shellfish committee here and we have a board of selectmen that understands the value, not only historically, but moneywise.”

In 2014, five fishermen that had expressed interest in full-time or near full-time green crab trapping were chosen to participate the program. Those same five boats are still trapping. LaPreste said Ipswich trappers brought in 73,720 pounds of green crabs in 2014, earning a total of $23,900. Trappers earned 20 to 25 cents per pound of green crabs caught that year, totaling $8,900 in bounty culled from Ipswich’s shellfish enhancement fund.

When the Division of Marine Fisheries provided $15,000 in state funding, crabbers were paid a bounty of 40 cents per pound.

In 2015, trappers landed 46,571 pounds of green crab, earning $18,101.40 in bounty. Because state funding for green crab trapping had been cut, the town put up $25,000 in municipal funds to pay the bounty, which rose from 30 to 40 cents in early September because of low numbers early in the season. LaPreste said that in addition to the remaining $6,898.60 in municipal funds left over from 2015, he hopes Ipswich will allocate additional money to keep the trapping program going in 2016.

Paying to trap green crabs is a better use of town funds than seeding clam beds, which are especially easy prey for the scavenger, LaPreste said.

“We were setting seed down, but right now, trapping green crabs gets you more bang for your buck,” LaPreste said. “Crabs will eat hundreds of thousands of juvenile clams. They just crush them. If you take the crabs, you’re letting the little clams have time to settle in and grow.”

Many are eager to get in on the hunt, but LaPreste said that a five-trapper program is most efficient. A larger program would be difficult to manage for one shellfish constable, LaPreste said, and ensuring that trappers have a large enough area to remain profitable is crucial to keeping the program running.

“I want to give these guys a big area to make it worth it for them,” LaPreste said. “For the program, we want to get as many as we can as fast as we can. We’ve got a nice system down.”

Green crabbing is becoming more lucrative as the trapping program is streamlined. LaPreste said that trappers composted most of their catch the first year, but in 2015, they were able to sell their entire green crab haul for bait on top of the bounty.

“We have no problem with that,” LaPreste said. “It gives them more incentive. We want the crabs out of the water. That’s my goal. If people make more money, God bless them.”

Data collection just begun

Though green crabs have scuttled around the northeastern shores of the U.S. for nearly a century, people are just starting to collect data that will measure their consequence to the clamming industry and the local environment.

Researchers don’t know why, for example, the green crab trapping haul dropped from 73,720 pounds in 2014 to 46,571 pounds in 2015. A colder winter and trapping may have combined to cut the green crab population. But no one knows for sure.

Boston University Research Professor Alyssa Novak is a member of the Great Marsh Resiliency Task Force, a group working to restore the Great Marsh to protect the area from devastating coastal storms. Novak became interested in the green crab population when the group began to notice that efforts to restore eelgrass beds in Plum Island Sound were being thwarted. The culprit? The green crab.

“As we planted the eelgrass, the crabs were ripping it up,” Novak said. “You plant eelgrass, they immediately come within five minutes.”

Eelgrass is a meadow-like haven to many species including scallops, crabs, fish and other important wildlife, providing food, oxygen, protection and nursery grounds according to the National Oceanic and Atmospheric Administration.

Eelgrass is also a valuable resource for people. The grass filters polluted runoff and protects shorelines from erosion by absorbing wave energy.

In addition to their taste for eelgrass, green crabs will burrow into marsh banks and further erosion, Novak said.

In 2013, Novak started to gather data about the area green crab population by starting a monitoring program, throwing out traps and counting the number of green crabs caught in a 24-hour period. Novak said the numbers of green crabs pulled out of the traps haven’t changed much since the monitoring program began.

“In 2015, you could get a trap with anywhere between 15 and 500 green crabs,” Novak said. “That’s very high. There is definitely a big problem.”

Division of Marine Fisheries biologist Kelly Whitmore said that because there is no fishery — no commercial market — for green crabs, the state hasn’t conducted an abundance survey.

“We would be doing an assessment of some sort, but it’s not a fishery so we don’t know how the populations have changed,” Whitmore said.

Novak said reaching a population estimate through research like the monitoring program is crucial to attracting attention and funding to the green crab problem on the North Shore.

“You can’t start managing if you don’t know what’s in the system,” Novak said. “You need to be able to show with data that the green crab is having an impact.”

Is trapping effective?

Right now, evidence of the problem and the effectiveness of trapping is largely anecdotal.

LaPreste said that he’s consistently amazed at the number of green crabs trappers haul out of Ipswich waters.

“You throw in your trap, you fill it, you throw it in, and it’s filled again in two hours, you go back the next day, it’s filled again,” LaPreste said. “It’s like, man, how many are in here?”

LaPreste thinks the trapping program is starting to make a difference, however slowly. In 2015, trappers didn’t start landing a large number of green crabs until September. Unfortunately, when trappers did start catching them, the green crabs were bigger and stronger than the year before, LaPreste said.

“You can’t find a book that tells you,” LaPreste said. “We don’t know how many clams were saved, but look at the numbers we’re pulling out. It has to make an impact, it just has to, but we can’t prove that. One thing people said in the fall when the oystermen came back was, ‘I’m not raking up the green crabs like I was last year.’ That’s because we trapped that area heavily. That right there said to me we made an impact.”

Some researchers are skeptical that trapping will make a significant impact on the green crab population.

Massachusetts Institute of Technology research affiliate Dr. Judith Pederson said that green crabs are here to stay for the foreseeable future.

“Trying to reduce the population by trapping is difficult,” Pederson said. “There’s just so many out there.”

Coastal Resources Coordinator for Massachusetts Bays National Estuary Program Peter Phippen agreed that eradicating green crabs through trapping is unlikely.

“All we can really do is manage their numbers,” Phippen said. “People are trapping between a million and a million and a half in the Essex River in one fall period.”