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Latest Research Boosts Protection for Oyster Production

 


They had the right idea, but blamed the wrong culprit.

Researchers from Oregon State University (OSU), the US Department of Agriculture (USDA), and Rutgers University recently announced that scientists have, for many years, misidentified the bacteria they blamed for playing a role in the Pacific Northwest shellfish industry’s woes in particular the near-demise of two major oyster hatcheries. In addition, the newly recognized bacteria are even more widespread and deadly than the previous suspect.

The findings – published in November 2014 in the scientific journal Applied and Environmental Microbiology – indicate that the primary bacteria causing the deaths of oyster larvae in the Pacific Northwest is a pathogen scientifically known as Vibrio coralliilyticus, not Vibrio tubiashii as they previously thought. The reason for the error is bacterial family resemblance: Claudia Hase, an OSU expert in microbial pathogenesis, said the two pathogens are essentially kissing cousins, which share similar gene sequences.

“V. coralliilyticus was believed to primarily infect warm water corals and contributes to coral bleaching around the world,” she noted. “But when we finally were able to compare the entire genomes, it became apparent that most of what we’re dealing with in the Pacific Northwest is V. coralliilyticus.”

Not only is V. coralliilyticus far more widespread than researchers originally determined, but they say it’s much more virulent to Pacific oysters, and can infect a variety of shellfish and fish, among them rainbow trout and larval brine shrimp.

This determination follows in the wake of the discovery of other causes behind a nearly decade-long decline in Pacific Northwest seed oyster production.

Oceanic Acid Reflux

In 2005, wild and hatchery oysters along the Washington and Oregon coasts – among them Whisky Creek Shellfish Hatchery in Netarts Bay, Oregon, Taylor Shellfish Farms on Dabob Bay in Quilcene, Washington, and several hatcheries on Willapa Bay, Washington – began to die off by the millions in their larval stages. Between 2006 and 2008, mortality rates rose as high as 80 percent, shoving the commercial oyster seed industry and the lucrative 150-year-old Pacific Northwest shellfish business to the brink of collapse. Initial concerns focused on viral or bacterial infection, prompting hatchery managers to instigate extensive, expensive, primarily ineffective anti-bacterial measures to filter out pathogens and disinfect incoming water. In 2008, researchers from OSU and the National Oceanic and Atmospheric Administration (NOAA) suggested another culprit: changing ocean chemistry, known as ocean acidification, triggered by greenhouse gas emissions, and specifically, carbon dioxide.

Researchers said the quickly changing chemistry endangers the ocean’s ecology, and acidification is a looming threat to the marine environment, economy and food web worldwide. Highly acidic oceans could – as industry managers have already discovered – severely impact, if not destroy, the livelihoods dependent on the $270 million shellfish industry in Oregon and Washington. But in 2008, the connection between rising acidity in seawater and its alleged adverse effects on oyster production was a theory without definitive proof.

So marine science investigators went on a quest to learn more about rising ocean acidity levels, the potential threat it poses to life in the sea, and find ways to make those levels ebb.

OSU researchers George Waldbusser, Burke Hales, Brian Haley and Chris Langdon began delving deeply into the matter in 2010, using funding from the National Science Foundation (NSF) to pursue two projects: one focused on determining the threshold at which oysters, mussels and clams are adversely affected by acidification, the other involved monitoring ocean chemistry in the California Current System and how wild mussels and sea urchins respond to altered ocean chemistry. In 2012, they announced finding a clear connection between acidification and the oyster seed production woes at the Whisky Creek hatchery. Elevated carbon dioxide levels in seawater, they noted, inhibit larval oysters from developing their shells and growing at a pace to make commercial production cost-effective.

“This is one of the first times that we have been able to show how ocean acidification affects oyster larval development at a critical life stage,” Hales said about their findings.

Documenting the connections among shell formation rate, available energy and sensitivity to acidification is a vital key to resolving the infant mortality undermining the shellfish industry.

Waldbusser said it’s not a case of acidity dissolving oyster shells, but more one of higher carbon dioxide levels in the acidic water altering and inhibiting shell formation rates. The fledgling oysters must use too much energy in trying to build their shells as quickly as possible, and the effort literally kills them. Researchers say adult oysters and other shellfish can fend off the ill effects by slowing their growth rates, but the oyster larvae lack the option: they must grow their first shells quickly, which is almost impossible under higher acidic conditions, or perish.

“The failure of oyster seed production in Pacific Northwest coastal waters is one of the most graphic examples of ocean acidification’s effects on important commercial shellfish,” said David Garrison, program director for the NSF’s division of ocean sciences.

Antacids and Assays

While simple chemistry is causing the problems, complex solutions are needed to ameliorate or eliminate those problems.

Hatchery managers acting to preserve the genetic foundation of the Pacific Northwest shellfish industry are open to almost anything. They have initiated protocols focused on water quality to offset the effects of acidic ocean water drawn from their respective bays. Monitoring and controlling water acidity have allowed hatcheries to regain most of their productive capabilities, but those measures might provide merely a temporary reprieve.

Oxygen depletion and rising water temperatures are contributing factors, as are patterns of ocean circulation and bacterial infection.

When seasonal wind patterns change in the spring, north winds create upwellings of deep, more acidic seawater off the Pacific Northwest coast. The colder, more acidic water, which lacks the oxygen and calcium shellfish need to build their shells, wells up from the ocean depths into bays, estuaries and other nearshore areas. It combines with land-based nutrient runoff from farming and other human activities to spawn algae growth, which lowers pH levels, making water even more acidic.

Major bacterial outbreaks produce toxins that can kill seed oysters in hatcheries if they reach high concentrations. OSU experts have developed a new precise, inexpensive and quicker test that, once perfected and commercialized, should provide oyster growers with an early warning system to detect the presence of high toxin levels, giving them time to quell the disease before it becomes an epidemic.

Lack of funding for identification and studies of the bacteria bogged down research efforts to pinpoint the actual culprit. Backed by NOAA and the USDA, researchers were able to differentiate the bacterial strains and develop the test.

Hase said V. tubiashii did not show significant pathogenicity to Pacific oysters, while V. coralliilyticus is highly infectious to both Pacific and Eastern oyster larvae, and possibly other shellfish species. “The Vibrio genus and many bacteria associated with it are a huge problem in fish and shellfish aquaculture, and we should be studying them more aggressively,” she noted. “V. coralliilyticus, in particular, has a very powerful toxin delivery system, and vibrios are some of the smartest of all bacteria. They can smell, sense things, and swim toward a host.”

Scientists linked vibriosis in various marine species to major problems worldwide since the late 1970s, but Hase said they knew very little about the bacteria itself and its toxins until now.

“It secretes a compound that’s toxic to shellfish, and that’s what our new assay is able to detect,” she noted. The test involves a process similar to a human pregnancy test that detects the presence of the specific toxic protein the bacteria produce. Once it is commercially established, the new test can provide results in about 30 minutes, compared to the three or four days required with other methods. The quick turnaround would give oyster growers a chance to do something before a situation escalates out of control.

The new diagnostic test has positive implications for other marine aquaculture species that depend on hatchery and nursery production of large quantities of high quality, disease-free larvae. Vibrio bacteria – along with the other factors that cause hatchery mortality – are also a significant concern among wild oysters and other wild shellfish along the Pacific coast.

Other strategies are also emerging to assist embattled shellfish producers.

“One possibility is to breed for specific genetic traits,” said Chris Langdon, who directed the molluscan broodstock program for many years at OSU’s Hatfield Marine Science Center in Newport, Ore. He is leading efforts to use selective breeding to isolate favorable traits in oysters that could protect them from the ravages of the ocean’s rising acidity and other issues such as bacterial diseases. Even so, researchers say the rise in environmental stresses from a changing ocean could make oysters and other marine life more vulnerable to bacterial infection, further complicating the process of finding remedies. Timely information is invaluable.

The ‘Burke-o-Lator’

NOAA recently launched the US Integrated Ocean Observing System (IOOS)’s Pacific Region Ocean Acidification Data Portal, to provide real-time ocean acidification data along the entire Pacific coast. The collaborative effort is led by University of Washington (UW) oceanographer Jan Newton, who said the system “makes valuable data more easily accessible, and will increase scientific understanding of how similar or different conditions are throughout the Pacific.”

IOOS offers real-time ocean chemistry data for the Pacific coast and some Pacific islands, as well as protected bays and shellfish hatcheries in Washington, Oregon, California and Alaska.

“For shellfish growers, having access to the data off their local site is important, but the oceanic data is an advanced warning system,” said Newton, who directs the center that acts as a clearinghouse for Washington and Oregon coastal observations on everything from boating conditions to toxic algal blooms.

Shellfish growers can use system information to decide when to grow larvae, when to set baby oysters in the field, when to draw the thousands of gallons of seawater needed to fill their tanks, and when they might want to take steps to alter the chemistry of intake waters.

The interactive portal created by UW oceanographer Emilio Mayorga and engineer Troy Tanner is adapted from a tool NANOOS launched in 2009. It not only compiles data from NANOOS and four other regional centers, but uses new sensors developed by OSU researcher and UW alumnus Burke Hales. Nicknamed “the Burke-o-lator,” the sensors can detect the suitability of ocean waters to form aragonite – a specific form of calcium carbonate mineral that clams, mussels and oysters use to forge their protective shells. As one of the most soluble forms of calcium carbonate, aragonite is especially sensitive to ocean chemistry changes.

The portal includes readings from Burke-o-lators at several coastal locations.

The Oregon legislature funded the first deployment at the Whiskey Creek Shellfish Hatchery. The Washington legislature funded the UW-based Washington Ocean Acidification Center (WOAC) was funded to install Burke-o-lators at a hatchery operated by Taylor Shellfish Farms in Puget Sound’s Hood Canal and at a shellfish growing site in Willapa Bay. The federal government is funding sensors at Alutiiq Pride Shellfish Hatchery in Alaska, Hog Island Oyster Co. in central California, and Carlsbad Aquafarm in southern California. Other monitoring sites feeding into the portal include commercial shellfish beds, the Seattle Aquarium, big offshore buoys that record weather and ocean conditions, and solar-powered ocean sensors deployed by UW researchers in Hood Canal and other Puget Sound locations. Several moorings deployed by NOAA’s Seattle-based Pacific Marine Environmental Laboratory (PMEL) to measure ocean acidification in Hawaii, Alaska and California waters also provide data.

Researchers will use information gleaned from the system to understand changes in water chemistry, and researchers with the Washington Ocean Acidification Center will interpret the data and look for trends.

“All of us will continue to serve our data on our own regional portals, because it’s very important to connect to local communities,” Newton said. “But in some cases you want to take a wider look at things.”

Oysters and shellfish could provide early warnings to enhance that “wider look.”

Global Phenomenon, Local Effects

Different species respond differently to altered seawater chemistry, but overall what’s happening among the shellfish is a microcosm of what’s happening elsewhere throughout the ocean. On-going climate change is the underlying and overarching component wreaking havoc on oysters and other shellfish, which researchers say could become harbingers of looming problems for other marine life. Among other things, scientists claim climate change causes a surge in upwelling, which enhances acidification, which adversely affects oysters and other shellfish, because they are especially vulnerable.

NOAA leaders say research will become more vital as ocean conditions and the fundamental chemistry of seawater continue to change for whatever reason. The economic and social impacts of this global phenomenon are already being felt regionally and locally.

 
 

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