This summer, divers discovered invasive red seaweed in the waters off of Cape Elizabeth. The Asian seaweed, Heterosiphonia japonica, has been making its way up the coast since establishing itself in Rhode Island around 2009, and it has been causing problems for lobstermen and beachgoers along the way. There is concern among scientists that the invasive species could push out native seaweed and damage eelgrass nurseries along the coast.
Divers connected with Northeastern University’s Marine Science Center in Massachusetts discovered the red seaweed in Maine waters, said Matt Bracken, a marine biology professor with the university. Though the seaweed had previously been spotted near Maine’s southern border, the discovery that it had leapt northward still came as a surprise.
“We had thought that originally we wouldn’t find it north of Cape Ann” in Massachusetts, he said.
The seaweed had only come to Massachusetts in the last two years, but it has quickly established itself. A Boston Globe story reported that the washed-up seaweed has caused havoc for beach communities north of Boston. It lets off a noxious odor as it decays, officials said. Lobstermen also have reported finding traps clogged with the stuff after storms.
But the larger problem may be how successful the seaweed is at outcompeting native species, Bracken said. In some areas, the seaweed has accounted for some 90 percent of biomass. With a natural aquatic range of just below the tideline to a depth of 30 feet, it grows on top of native seaweed and oysters, pushing out native species and clogging their ability to filter the water and clean the ecosystem. It also lodges itself in eelgrass, which is a vital nursery habitat for lobster and many groundfish, Bracken said.
So far, scientists haven’t discovered a way to control the seaweed, and natural checks and balances aren’t working, he said. Aquatic herbivores, so far, don’t want to eat the seaweed. Sea urchins might have aided in beating the seaweed back, Bracken speculated, but their population in the Gulf of Maine is in trouble. Eventually, a species may adapt and begin to control the seaweed, but Bracken and his team is also exploring ways to dislodge the seaweed when it is at its weakest.
“It’s plentiful in some times and in some cases,” Bracken said. “It goes through boom and bust cycles.”
The spread is a concern for Maine’s seaweed harvesters, said Shep Erhart, founder of Maine Coast Sea Vegetables. The initial reports of the seaweed’s reach seem to indicate that it could affect some of the native seaweed varieties harvested by Maine businesses, while leaving others alone, he said. The seaweed industry is already grappling with the apparent effects of climate change on native seaweed, and this adds another stress, he said.
“This is definitely a threat to the species that are natural,” Erhart said.
The seaweed found on the East Coast is actually cloned from the invasive seaweed in Europe, said Craig Schneider, a biology professor at Trinity College in Connecticut. Schneider was the first to discover that the species had landed in the U.S. A taxonomist, he came across the seaweed while walking on the beach in Rhode Island. While it is hard for a layman to tell the difference between this seaweed and others, Schneider noticed a batch of seaweed that looked slightly different than the rest. He took a lab sample and found that it was an exact genetic match for the seaweed in Europe, as the invasive plant reproduces copies of itself asexually. Knowing what had happened in Europe when the seaweed landed there and noting how the seaweed was well established on the outer Rhode Island beach, he knew it needed to be labeled an invasive species right away.
“It was already successful,” Schneider said. “It was already here, had been here for years.”
An invasive species along the coastline can be much more difficult to control than an inland invasive, Schneider said. Introducing a biological agent to control it can have unintended consequences for the rest of the fragile shoreline ecosystem, and the sheer quantity of coastline makes any control efforts difficult.
“How do you treat something in fairly shallow waters?” Schneider asked. “It’s overwhelming.
Craig Idlebrook is a freelance contributor living in Medford, Mass.