BLUE HILL — It’s no secret that the waters of the Gulf of Maine are getting warmer. Although many fishermen say that this summer the water around Downeast Maine has been colder than in recent years, according to data compiled by the Gulf of Maine Research Institute, from 2004 to 2013, water surface temperatures rose faster in the Gulf of Maine than in 99.9 percent of the global ocean.
Cold or warm, this year strange critters have made themselves at home in local waters, some of them apparently settling in Downeast Maine for the first time.
Blue Hill is hardly a lobster fishing hotspot like Stonington, but over the past several years, a good-sized fleet has grown up in the town’s three harbors.
Some of the boats and fishermen are relative newcomers, but Surry fisherman Paul Raspante has been lobster fishing in Blue Hill Bay for nearly 35 years. Since 1990, he has hauled gear from the Jana Morgan, a 22-footer he built himself.
Over the years, Raspante has found all kinds of marine life in, and on his traps: lobsters and crabs, of course, starfish, sea urchins, even the occasional cod.
This year, though, he saw something completely new. As the season progressed through summer, his traps became more and more heavily fouled with squishy, translucent jar-shaped blobs a couple of inches long.
“I’ve been fishing here for 35 years and I’ve never seen these before,” Raspante said while taking up a load of traps from around Darling Ledge for the winter.
Some of the organisms clinging to the wire traps had a smooth surface, others were covered with tiny bumps. After some online research, Raspante took some sample organisms to the Marine and Environmental Research Institute in Blue Hill. There Courtney Neumann, a monitoring assistant, helped him identify both as tunicates — commonly called sea squirts —invasive species that seem to be making their way farther eastward in Maine waters.
The bumpy critters are Ascidiella aspersa, a native of Europe that was most likely introduced to the United States from hull fouling or ballast water discharge from ocean-going ships.
First discovered in New England waters in the 1980s, by 2010 it could be found in the Gulf of Maine at least as far to the east as the North Shore of Massachusetts and now apparently has reached Blue Hill Bay.
The smooth critters are Corella eumyota, which is endemic to the oceans of the Southern Hemisphere. In 2002, the tunicate was discovered at two marinas on the French side of the English Channel. Now it is in Blue Hill Bay.
Besides being unsightly, and making lobster traps harder to clean, the invasive C. eumyota grows in large clumps, fouling floating docks, piers, ropes and other submerged structures.
A more serious problem is that these tunicates can eventually grow densely enough to smother colonies of oysters, mussels and other shellfish.
Scientists have been keeping an eye on another invasive critter referred to as a sea squirt, Didemnum vexillum, for more than 15 years. Initially seen around Georges Bank, it has more recently spread through nearshore and offshore regions. The bottom-smothering sea squirts have spread across the seafloor all the way to Eastport, in some areas displacing the animals that the gulf’s sea creatures actually want to eat. According to research by scientists at the University of New Hampshire, the barnacle and sea squirt populations have exploded since 2007.