Orange/red colonial tunicates engulf a mussel. Tunicates are an invasive marine species in Narragansett Bay.

On a cool Friday morning last month, a dozen curious Rhode Islanders lay down on the pier at Point Judith Marina to collect some of the squishy and crunchy creatures that were growing on the side of the docks. Using rusted metal spatulas, they scraped the unknown life into small aquarium nets and saved it in plastic tubs, then spent half an hour trying to identify what they had retrieved.

With the exception of a few blue mussels, almost nothing was recognizable. There were sea squirts and shrimp-like things, seaweeds and green crabs, and just about everything was covered in a mushy yellow-brown mat called a colonial tunicate.

Almost none of it was native to New England waters. In fact, most it came from the other side of the planet.

Marine invasive species are a growing problem. According to Kevin Cute of the Coastal Resources Management Council, who led the marina program sponsored by Rhode Island Sea Grant, there is little that can be done about them. Once a new species arrives, it’s almost impossible to get rid of it. So prevention is the key, he said.

But preventing marine organisms from showing up where they don’t belong is harder than you would think. Most arrive in the ballast water of ships, which pump entire marine ecosystems from one part of the world into their hulls to improve the ship’s stability, and then they discharge it into water bodies far from where they originated.

Since the biochemistry of Narragansett Bay is far different from that of the South China Sea, for instance, most microscopic organisms cannot survive in both places. But a few hardy specimens endure the journey, latch onto a hard surface like a rock or marina pier, and start to reproduce. And it’s nearly impossible to stop them.

The colonial tunicate that covered most of the other creatures at Point Judith Marina that day originated in Japan, showed up in Maine in 1993, and has been spreading along the East Coast ever since. With no known predators, it grows aggressively, fouls fishing and aquaculture gear, and smothers shellfish and other creatures living on the seafloor.

Cute and a team of CRMC staff and volunteers conduct monthly sampling for marine invasive species at five sites around Narragansett Bay to keep an eye on the known invaders and to watch for new arrivals. But, he said, “there are so many variables – storm events, changing temperatures and salinity, predation, competitors – if I came back next week there could be very different species here.”

Various regulatory agencies are doing what they can to restrict the arrival of new organisms. Ships entering U.S. waters are now required to dump their ballast water at least 200 miles from shore. And some ships must install on-board chemical or ultraviolet systems for treating their ballast water before discharging it – though many in the shipping industry are fighting these regulations.

So while it is getting more difficult for new species to make it to our shores, dealing with the species that are already here is a never-ending battle. The colonial tunicate is an especially challenging one to manage. It’s already affecting Narragansett Bay’s eelgrass beds, which Cute calls the most important habitat in the bay because it is a valuable nursery area for fish.

“We’re playing ecological roulette with invasive species,” Cute said. “They’re wiping out dinner for all of us.”

Naturalist Todd McLeish has been writing about wildlife and the environment for more than 25 years. His latest book is “Narwhals: Arctic Whales in a Melting World.”

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