LEFT: Sara Randall, the local scientific coordinator for the upweller project, checks on the development of the 1 million juvenile clams growing in the upweller on the Harraseeket River. Next year the soft-shell clams will be transplanted to plots in Freeport to grow under protective netting.
S oft-shell clams are getting a new lease on life in Downeast Institute’s upweller, a spat — or juvenile clam — nursery in Freeport.
ABOVE: A tube with hatchery spat, or juvenile clams, shows the size the soft-shell clams are before they are put in the upweller. The clams have shown rapid growth in the upweller, which provides a nutrient-rich habitat safe from predation, said Sara Randall.
The upweller is a system of 20 large barrels half submerged in the water, anchored to a float with a water pump system. Spat rest in the bottom of each barrel on a mesh net, feeding from fresh water which is continually filtered up through each barrel, emptying into a central tank.
“It’s essentially like a farm,” said Randall. “In the wild, soft-shell clams release their eggs into the water and they travel and settle into the mud,” but in recent years, the invasive European green crabs have fed on and devastated wild soft-shell clam populations.
“We have a lot of tiny green crabs out right now and tiny green crabs can only eat things that are about their size,” said Randall, noting that the juvenile clams were prime targets.
“Right now they’re not settling into the mud, they’re in these barrels and in these barrels they’re protected from predation, which is the thing that we’re most concerned about,” she said.
Downeast Institute estimated that currently 90 percent of Casco Bay, which was once a very productive habitat, is now non-productive in softshell clams, said Randall.
Green crabs have inhabited Maine subtidal areas, which remain submerged in water, and intertidal areas, which drain at low tide, for 150 years, said Randall, but the recent population explosion has endangered native marine resources.
“The fishermen noticed it first with the loss of the blue mussels, which we learned through scientific research is the preferred food of the green crab,” said Randall, adding that green crabs may also be responsible for depleted urchin and scallop populations, which occupy the same habitat.
“It took a while, after they went through other food sources, to get to the clams,” said Randall. “And soft-shell clams are the bread and butter of our coastal economy.”
Planted one month ago, the clams “have shown incredible growth already,” said Randall. “There appears to be a lot of phytoplankton in the Harraseeket River, which could be because these clams aren’t really competing with many other clams for food — there just aren’t that many left.”
The soft-shelled clams are filter feeders, said Randall, which feed through a siphon, filtering plankton out of the water and helping to maintain good water quality in the marine ecosystem.
The clams will be raised in the upweller to a transplantable size, said Randall, and eventually planted in Freeport waters next spring under protective nets in hopes that this and other efforts will help the dwindling population rebound.
“The upweller is just one part of a larger, comprehensive project looking at ways to protect soft-shell clam populations,” said Randall, who is working on five other coinciding studies that are being headed by professor Brian Beal at the University of Maine at Machias and Downeast Institute in partnership with Stewards of the Sea LLC.
In Staples Cove, 14 30-by-30 foot fenced units have been placed in areas to determine if fencing is effective in deterring green crab predation of cultured and wild soft-shell clams. Samples will be taken in November and compared to control plots to determine the fencing’s efficacy.
Experiments on mitigating ocean acidification using crushed and weathered clam shells is also taking place in Staples Cove, which has the lowest pH in the area, making it a particularly inhospitable environment for juvenile clams.
Green crab trapping has also been occurring since the beginning of May, said Randall and will continue through October, to see if trapping can reduce local populations and also to survey trends in abundance, size, sex-ratio and diet.
While fewer crabs have been trapped this year than were trapped during a similar effort last year, Randall said that even if some winter dieoff has occurred as a result of last winter’s extreme cold temperature, she still thinks the population poses a significant problem.
“Research we’ve found of green crabs in their native habitat in Europe shows that in a colder winter it takes longer for them to come into the intertidal areas,” said Randall, who expects to see larger numbers in late July and August.
“During the winter, the bigger crabs at least are out in the subtidal area where it’s warmer,” she said, “so we’re just waiting to see when they will hit.”
In Spar Cove and Recompence Flat, a study is being carried out to determine if wild spat will be attracted to and tend to settle in areas where there is a large population of adult soft-shell clams, while in Collin’s Cove and Wolfe’s Neck, hatchery-reared juvenile clams have been planted at different densities under netting to determine the success of clam enhancement using cultured clam seed.
The upweller, though, is a unique aspect of the diverse soft-shell clam experiments being carried out, said Randall.
“None of us had worked on an upweller before,” said Randall, noting that a local contractor had built and modified the basic upweller design. “It’s a very rare thing that we have going on right now, particularly for soft-shell clams.
“This is the most comprehensive study of its kind,” she added, “definitely in Maine’s history and probably in New England.”
rgargiulo@timesrecord.com
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