Coastal Dead Zones May Benefit Some Species, Scientist Finds

Coastal dead zones, an increasing concern to ecologists, the fishing industry and the public, may not be as devoid of life after all. A Brown scientist has found that dead zones do indeed support marine life, and that at least one commercially valuable clam actually benefits from oxygen-depleted waters.

Andrew Altieri, a post-doctoral researcher in the Department of Ecology and Evolutionary Biology at Brown University, studied dead zones in Narragansett Bay, one of the largest estuaries on the U.S. East Coast. In a paper published this month in the journal Ecology, he found that quahog clams (Mercenaria mercenaria) increased in number in hypoxic zones, defined as areas where dissolved oxygen in the water has been depleted. The reasons appear to be twofold: The quahogs’ natural ability to withstand oxygen-starved waters, coupled with their predators' inability to survive in dead zones. The result: The quahog can not only survive, but in the absence of predators, can actually thrive.
A recent study shows that dead zones have been expanding rapidly along the coastal United States and worldwide due to climate change and human-caused pollution. Scientists have typically focused on documenting the death of species and loss of fisheries in these oxygen-poor areas, but they haven’t looked at how certain, hardy species such as quahogs can persist and thrive — until now. There may be other commercially important species that persist — and perhaps benefit — from dead zones in other regions.
The research (listen to the podcast on the Ecological Society of America Web site here) also underscores that some key species can be more adaptive and resilient than expected when challenged environmentally, which could have important implications for conservation efforts.
“You’d be hard pressed to say dead zones are good,” Altieri said, “but with this study you just can't say that dead zones are simply doom and gloom. Ultimately, it’s a silver lining on a very dark cloud.”
Altieri planted quahogs, soft-shell clams (Mya arenaria) and blue mussels (Mytilus edulis) at four locations in Narragansett Bay — three of which are known to become hypoxic seasonally. He monitored how the species’ populations fared during summer and early fall in 2003 and 2004 — periods when hypoxia is most likely to occur. Altieri found that all three bivalve species can tolerate mild hypoxic conditions, and that each benefited from some degree of hypoxia, because their natural predators vacated those zones. Scientists call hypoxia's benefit to aquatic prey species “predation refuge.”
Altieri also determined that only the quahog can survive during severe hypoxia. In fact, he found the clam’s density was highest in the most oxygen-challenged areas, while the other species died off, as expected in a dead zone.
“The quahogs are benefiting from the dead zones,” Altieri said. “That was not something that we would have predicted from the conventional wisdom on dead zones or laboratory experiments alone.”
The quahog is an iconic symbol in Rhode Island and even nationally and is the dominant catch in the Ocean State’s shellfish industry. In 2007, the quahog’s landed value was $8.4 million, according to the Rhode Island Department of Environmental Management's Division of Marine Fisheries.
In an odd twist, Altieri found that quahog populations declined in healthier waters. He thinks it’s because the predators return as oxygen levels in the water rise, and those hunters — primarily sea stars, fish and crabs — feast on the clams. That means quahogs could fare worse if Narragansett Bay’s waters got cleaner.
Yet Altieri is not advocating that hypoxic zones remain. While the quahog is shown to benefit from dead zones in Narragansett Bay, it is the only marine organism he found to do so. That means fishery managers, scientists or others could misjudge the health of a coastal ecosystem by the abundance of a particular species, while failing to see the losses of other species in that system.
“You say we’ve got this great fishery, what’s the problem? But the ecosystem underpinning it may be hanging on the fact that one species is doing great, and the others may not be,” Altieri said. “In the case of Narragansett Bay, if we lose the quahog because of further declines in water quality, disease, or some other factor, we won’t have another species to turn to.”
The research was funded by the Rhode Island Sea Grant College Program, the National Oceanic and Atmospheric Administration’s National Estuarine Research Reserve System (NERRS) Graduate Research Fellowship, the U.S. Environmental Protection Agency, the Lerner-Gray Grants for Marine Research through the American Museum of Natural History and the Sounds Conservancy Grants Program through the Quebec Labrador Foundation.
Adapted from materials provided by Brown University.

Longest Living Animal Clam 400 Years Old Found In Icelandic Waters

A clam dredged from Icelandic waters had lived for 400 years - is this the longest-lived animal known to science?

Can you imagine living for four centuries? A team of scientists from Bangor University's School of Ocean Sciences believe they have found an animal which did just that, a quahog clam, Arctica islandica, which was living and growing on the seabed in the cold waters off the north coast of Iceland for around 400 years.
When this animal was a juvenile, King James I replaced Queen Elizabeth I as English monarch, Shakespeare was writing his greatest plays Hamlet, Othello, King Lear and Macbeth and Giordano Bruno was burnt at the stake for espousing the view that the Sun rather than the Earth was the centre of the universe.
According to the Guinness Book of Records, the existing record for the longest-lived animal belongs to a 220 year old Arctica clam collected in 1982 from American waters. Unofficially, the record belongs to a 374 year old Icelandic clam which was found in a museum. Both these records appear to have been eclipsed by the latest specimen, whose age, between 405 and 410 years, has been assessed by counting the annual growth lines in the shell.
The Bangor scientists are sclerochronologists who study the growth and age of clams using annual growth lines in the shell in much the same way as dendrochronologists study the growth of trees using tree-rings. Clam shell growth is related to environmental conditions such as seawater temperature, salinity and food availability. The team analyse the shell growth histories with a view to understanding changes in the ocean linked to climate change.
The clam was dredged up by Team members Paul Butler and James Scourse during a data collection cruise in Icelandic coastal waters in 2006 which formed part of the EU MILLENNIUM project investigating climate changes over the last 1000 years. The exciting discovery was made by postdoctoral scientist Al Wanamaker, the newest member of the ‘Arctica’ team. “Al and Paul rushed up to my office to announce that they had found a record-breaker,” said team member Chris Richardson. A detailed assessment later confirmed that, at 400 years, the clam had beaten the previous record by a massive 30 years!!
It is very likely that longer lived individuals of the species remain to be found. Although Icelandic waters seem to provide the ideal conditions for extreme longevity, clams with lifetimes well in excess of 200 years have been found both in the Irish Sea and the North Sea.
So why do these clams live so long? The Bangor scientists are intrigued to find out and believe that the clams may have evolved exceptionally effective defences which hold back the destructive ageing processes that normally occur. "If, in Arctica islandica, evolution has created a model of successful resistance to the damage of ageing, it is possible that an investigation of the tissues of these real life Methuselahs might help us to understand the processes of ageing," explains Chris.
This ageing aspect is now going to be funded by a new grant to the team from Help the Aged.
Adapted from materials provided by Bangor University.

Invasive species is found on key shellfish habitat: eelgrass

Over the last 10 years, Mary Carman has documented how slimy sea squirts have invaded coastal New England, multiplying on rocks, docks, boat bottoms, moorings, and other hard surfaces. Their rubbery bodies create a nuisance and, perhaps more importantly, render some areas uninhabitable for native species of oysters, mussels, scallops, and other marine life.
Until this summer, Carman had only rarely seen the creatures anchoring themselves to softer structures. So she did a double take when she spotted two sea squirts that she studies, known to scientists as Didemnum vexillum and Dipolsoma listerinum, clinging to acres of underwater eelgrass. The thick, waving meadows of eelgrass provide crucial nurseries for sea life, and are a prime habitat for prized shellfish—bay scallops.
Carman, a researcher at Woods Hole Oceanographic Institution, found sea squirts coating eelgrass in Sengekontacket Pond and Lake Tashmoo on Martha’s Vineyard, Mass. Under ordinary circumstances, juvenile scallops dangle from eelgrass blades like holiday ornaments, until they grow big enough to release their hold and then swim freely or rest in sediments. But in these spots at least, sea squirts were moving into the scallops' neighborhood.
Was this the first hint of a trend? Alarmed at the possibility, Carman contacted David Grunden, the shellfish constable in the island’s town of Oak Bluffs.
“We’re worried about it,” Grunden said. After seeing the sea squirts, he quickly agreed to partner with Carman to map their spread. “It’s a potential disaster if we find them growing on eelgrass in a large extent.”
(Mary Carman narrates a short video on her work mapping the spread of sea squirts that can have come from Europe and Asia and are crowding out native species of plants and animals. Watch the video »)
Clam copsMartha’s Vineyard shellfish fisheries are so important to the resort island off Cape Cod that each town has a shellfish constable. Locals sometimes jokingly call them “clam cops” and “shellfish sheriffs, ” but jobs like Grunden’s are serious—looking after bay scallops, oysters, clams, and other marine life that live in one of the nation’s most productive shellfish regions.
Though small in size, coastal Massachusetts is one of the top 10 producers of shellfish in the United States. Bay scallops have been important to its residents since colonial times, when settlers picked the shellfish by hand at low tide. At peaks in the 1980s, the state harvest exceeded 1,200 metric tons and was valued at $11 million. On Martha’s Vineyard, where people flock for summer vacations fueled by plates of fresh, garlic-and-butter-infused seafood, bay scallops remain ingrained in the island’s culture.
Since the 1980s, bay scallops—a species with a lifespan of just two years—have been in decline. Research suggests that an increase in nutrients (in the form of fertilizers and sewage from septic systems) that have flowed into coastal waters has spurred rampant growth of marine algae. This diminishes water quality and blankets the water surface, blocking sunlight from penetrating to eelgrass. An influx of sea squirts could make it even harder for bay scallop populations to survive.
One sunny Thursday morning before Labor Day weekend, Carman, Grunden, and several volunteers—including a concerned local fisherman, an underwater photographer, and Carman’s high-school-age daughter—motored into Major’s Cove in Sengekontacket Pond. Wearing snorkeling gear, they jumped overboard to find out just how much of the five-acre eelgrass meadow had been overtaken by sea squirts.
After diving about eight feet to the mucky bottom, Carman surfaced and gently spread several slender, bright green strands on the boat’s deck. Most of the blades were coated at least partially with sea squirts. They looked like rotten scrambled eggs and felt cold and slippery to the touch.
“Look how it is growing right next to the scallop,” she said, gesturing to a thumbnail-size shell attached to the plant. During the next two hours, she and the volunteers swam over the meadows, taking samples and marking locations using a handheld GPS unit.
“They are all the way to the beach, on both sides of the cove,” she said when she swam back to the boat. “They are definitely spreading. That’s not good.”
Sea squirt crusader Carman’s single-minded dedication to learning, and teaching others, about sea squirts began 10 years ago when she was a naturalist who coordinated youth education programs. To answer her students’ questions about the weird-looking, rubbery creature (which some kids called “alien vomit”), she began doing research. She quickly found no ready answers. Since then she has acquired grants and a place in the WHOI Geology and Geophysics Department.
Sea squirts feed on algae and bacteria, using one tube to suck in water and another tube to squirt it out (hence their name). They are tunicates, a name derived from a firm, rubbery outer covering called a “tunic.”
Of the nine types of sea squirts found on Cape Cod, six are invasive species introduced in the last 80 years from Asia and Europe. Carman’s research focuses on a species of the genus Didemnum, which forms dense mats from many small, linked individuals.
The creatures take over new areas in several ways, some traveling in from affected areas by clinging to boat bottoms or aquaculture gear, others by simply traveling from place to place by clinging to a piece of wood, a plastic bottle, or a blade of eelgrass.
“It’s a tremendous management challenge,” said James Carlton, a professor of marine sciences at Williams College in Connecticut. “We can tell the boater to scrub his boat bottom before he hauls it to new area, but how do you prevent grass with sea squirts clinging to it from rafting into new areas?”
On Martha’s Vineyard, with many connected waterways, Carman said it’s easy to imagine how easily they could move and settle into new areas.
“Everywhere I go on the Cape, I’m looking for them,” she said. Her daughter Mimi has been helping look for squirts since kindergarten. Now 16, she joins her mother on snorkeling excursions and can identify native and non-native sea squirts at a glance.
Growing concernOf their growth on Martha’s Vineyard, Carman said, “I’ve never see them in an open area like this and not to this extent.” In late September, she attended a workshop on aquatic invasive species where she confirmed with colleagues that Didemnum vexillum and Dipolsoma listerianum have not been previously documented growing on eelgrass. So far, Grunden said, sea squirts have not had a direct, negative impact on wild populations of bay scallops or on other shellfish that use eelgrass for habitat, such as oysters, quahogs, or clams. However, they are a nuisance to those in the aquaculture industry. They cling to aquaculture equipment, including cages used to encourage bay scallop spawning each year in several ponds on Martha’s Vineyard.
“Oyster farmers find Didemnum to be a pest species that impedes the flow of food and water, are time-consuming to remove, unsightly, and generally just a headache to deal with,” said Diane Murphy, who works with shellfish growers on Cape Cod and Martha’s Vineyard in her job with Cape Cod Cooperative Extension.
Fishermen also want to see less of them. Jeff Clements, a commercial shellfisherman in New England for 35 years, volunteered the use of his boat and time before Labor Day to help Carman’s research.
After toweling off in the boat, he said, “I’ve seen it over the years, but not in such quantities. It’s something I’m worried about.” —Amy E. NevalaFunding for Mary Carman's research came from the Sailors' Snug Harbor of Boston Foundation and the Link Foundation.

Deep in the ocean, a clam that acts like a plant

How does life survive in the black depths of the ocean? At the surface, sunlight allows green plants to "fix" carbon from the air to build their bodies. Around hydrothermal vents deep in the ocean live communities of giant clams with no gut and no functional digestive system, depending on symbiotic bacteria to use energy locked up in hydrogen sulfide to replace sunlight. Now, the genome of this symbiont has been completely sequenced and published in Science."The difference here is that while plants get their energy and carbon via photosynthesis by chloroplast symbionts, this clam gets its energy via chemosynthesis," said Jonathan Eisen, a professor at the UC Davis Genome Center and an author on the paper.The actual work of photosynthesis in green plants is done by chloroplasts, descended from primitive single-celled organisms that were incorporated into other cells billions of years ago."The energy from hydrogen sulfide is used to drive carbon fixation in much the same way that chloroplasts carry out carbon fixation," Eisen said. The symbiotic bacteria also fix nitrogen and produce amino acids, vitamins and other nutrients required by the clam.Studies of the deep sea have implications for studying the origins of life, Eisen said. Life on Earth may have got its start with microbes living on such chemical reactions, before the evolution of photosynthesis."And they're just plain interesting," Eisen added.If you were thinking that giant clams sound tasty, think again. The hydrogen sulfide gives them a strong smell of rotting eggs.The senior author on the paper is Colleen Cavanaugh at Harvard University, and the first author is a graduate student in her lab, Irene Newton. The other authors include researchers at Harvard, the Joint Genome Institute, Walnut Creek, Calif., and the Institute for Genomic Research in Rockville, Md.University of California, Davis.