Chesapeake Quarterly Volume 1, Number 3: Summary of Field Trial - C. ariakensis vs. C. virginica
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2002
Volume 1, Number 3
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Don Meritt picks up a clean oyster shell from a pile that fills a containerized steel cage - photo by Skip Brown
   

Don Meritt picks up a clean oyster shell from a pile that fills a containerized steel cage. Meritt and his colleagues will fill these cages with Choptank River water and add millions of newly spawned oyster larvae. The larvae will feed in the tanks until they grow large enough to cement themselves to the shell, undergo metamorphosis and become spat that are ready for planting.

PROFILE

Don Meritt:
The Hatchery Connection

By Merrill Leffler

"Hatcheries can perhaps jump start
restoration if oysters survive so that they
can reproduce - then we can leave
the rest to Mother Nature."

Last year the Horn Point Laboratory hatchery produced more than 75 million disease-free oyster spat - these newly-set young, more than three times greater than the crop produced five years before, were placed in oyster sanctuaries and managed reserves, leased aquaculture grounds, community oyster gardens and used for a host of research and educational projects throughout the state. The hatchery at Horn Point - part of the University of Maryland Center for Environmental Science (UMCES) and located on the banks of the Choptank River just outside Cambridge on Maryland's Eastern Shore - has been responsible for nearly all of the hatchery-produced spat in Maryland.

The hatchery's increasing production, and its key role in oyster restoration in Maryland, is due in large measure to the efforts of Don Meritt (Mutt to everyone who knows him). Horn Point's wide-ranging cooperative arrangements, for example, with the Oyster Recovery Partnership (the non-profit organization that has expanded its coordination of restoration projects in Maryland over the last several years), the Maryland Department of Natural Resources (DNR), research labs, educational institutions, and community-based groups over the last decade, were not as inevitable as they may appear.

Meritt, a Horn Point faculty member and shellfish specialist for the Maryland Sea Grant Extension Program, began working for UMCES nearly 30 years ago at the Chesapeake Biological Laboratory, not long after finishing St. Mary's College. He was hired by Curt Rose to work at the hatchery that a group of faculty were developing - the initial goal was to test the potential for rehabilitating oyster stocks that had been devastated by Tropical Storm Agnes in 1972. The early plans were based largely on a commercial operation that John Dupuy developed at the Virginia Institute of Marine Science in conjunction with an oyster producer in Virginia. In the meantime, Rose left the university to work in private consulting. Meritt contacted George Krantz, then at the University of Miami but who had previously worked in Maryland where Meritt had met him, and told him about the job. Krantz applied and was hired to run the hatchery. During this time, UMCES moved the hatchery to the newly established Horn Point Lab and Meritt, with Krantz, went there as well.

When Krantz left in mid-eighties to work for DNR, Meritt took over - he has since moved the hatchery from a modest enterprise producing a million eyed larvae annually to one that last year produced three-and-a-half billion. While this number may seem mind-boggling, perhaps 10 to 20 percent survive the process of metamorphosis to become spat - thus last year's 75 million. What does that figure actually mean? Sanctuaries are generally planted with two million spat an acre, managed reserves and private leaseholds with one million. This means that last year's production could cover some 30 acres of sanctuaries and 60 acres of reserves. That is still a "drop in the bucket," Meritt says, at least in relation to the more than 200,000 acres of public oyster grounds in Maryland or even the 1000 acres of leaseholds that were once actively producing oysters until disease became so widespread.

And disease is the issue. How many of the hatchery oysters will survive MSX and Dermo? There is no easy generalization - it depends on a number of factors. For example, on water salinity: in salinities of 12 to 15 parts per thousand, oysters are especially vulnerable to Dermo (MSX operates more successfully above 15 ppt). And yet, if bottom grounds have been cleared of all oysters, then prepared with clean shell before planting the new spat, they have a better chance of surviving for years, says Kennedy Paynter of the University of Maryland College Park and the UMCES Chesapeake Biological Laboratory. That is because Dermo is transmitted from oyster to oyster - by clearing Dermo out of an area first, the hatchery-produced seed have a better chance of long-term survival. This is especially so in lower salinities -unfortunately, low salinities are not favorable to oyster recruitment.

Meritt has never advocated hatchery production being able to replace the reproduction of a healthy ecosystem. We might use it for restoring a small area, say 26,000 acres in the lower Choptank, he says, but you can't bring back 200,000 acres. "We can perhaps jump start it if the oysters survive so that they can reproduce - then we can leave the rest to Mother Nature."

By next year, Horn Point will have a much expanded hatchery as part of a new Aquaculture and Restoration Research facility. If all goes well, hatchery production could expand to 500 million spat, five times more than in 2001. What can be done with that increased output depends on where they are used. For argument's sake, Meritt says, assume they're all placed in sanctuaries: at one million spat an acre, that's 500 acres. Warming to this vision, he says, we might expect an average yield of 1000 bushels of three-inch oysters per acre - in this case, total production could reach 500,000 bushels, considerably more than public harvests have averaged over the last decade in Maryland. All this production from just one hatchery, he continues - imagine what many hatcheries or seed spat-producing facilities might contribute, especially if the oysters were able to survive disease and continually spawn new generations. The emphasis, however, is on "if" - native oysters in higher salinity waters are not generally surviving long enough to produce large numbers of larvae.

A Natural Biologist

As a youngster, Meritt did not imagine that he would one day be a scientist doing research in the waters he knew so well. A native of Maryland's Eastern Shore, he was raised in St. Michaels at a time "when all those little boutiques that now line main street were residences for people who worked on the water." On his mother's side, most of Meritt's uncles - and there were many - were farmers and watermen who tonged for oysters in the winter. Many of his friends from St. Michaels High School came from watermen families. "It was pretty natural to know what was going on in the water - all you needed was a license and a boat and you could go do it. You were your own boss." He had a rowing skiff early on and began making money from both soft and hard crabbing near shore as a kid. "I was probably in the 10th grade when I started trot lining [for crabs], and I did it all the way through college," he says. By high school, he was also shaft tonging for oysters as well, on the Miles River, Broad Creek and the Tred Avon.

bagged oyster shells near the Horn Point Hatchery - photo by Skip Brown Meritt was the first male in a large family on both sides to graduate from high school. Though he had thought about college he might well be a working waterman today, he says, if it wasn't for Dick Kleen, a teacher who had a great influence on his life. Kleen was an avid amateur ornithologist, dynamic and passionate, and his natural history club, which Meritt went into as a seventh grader, was his introduction to birding - "my first real passion in nature," he says. For a time, his goal was to go to Cornell and get a degree in ornithology.

He didn't make it to Cornell but instead to St. Mary's College on the western shore via two-and-a-half years at Chesapeake College. "It took me a while to transition from high school to college," he says with some amusement. It took more time and a good deal of serendipity to bring out what has become a profession and personal passion, growing oysters in numbers that can make a difference not just for the fishery or for aquaculture but the Bay system itself.

After graduation, Meritt spent time in the Florida Keys working for a commercial fisherman for some months before returning to St. Michaels - he picked up different jobs, working for the Department of Natural Resources one summer to eradicate water chestnut on the Bird River, crabbing and tonging for oysters and working on skipjacks as well. While he was working with several former St. Mary's College students on a Power Plant Siting program on the Potomac River headed by CBL scientist Joe Mihursky, the job came open in the fledgling oyster hatchery at the lab. It seemed like the thing to apply for.

The hatchery's resources were meager. "Our larval tanks were buckets," Meritt says, "and we were dealing with tens of thousands of larvae." It was around this time that the State of Maryland established UMCES on the former DuPont estate where the Horn Point Laboratory was to be constructed. When UMCES moved the hatchery project there, Meritt was happy to return to the Eastern Shore.

The hatchery was designed to produce "cultchless" oysters - oysters that set on a small chip and grow singly, not in clumps as they do in the wild and for current restoration programs in Maryland. Unprotected cultchless oysters are vulnerable to predation and need to be reared in confined systems such as floats in order to keep crabs, cownose rays and other predators from getting to them. This growing method is more expensive than growing "rocks" on the bottom, Meritt says. You then have to be able to sell them for enough to cover your costs - this usually means for the higher-priced half-shell market rather than the Chesapeake's traditional shucked meat market.

Initially, the hatchery was designed to do pilot-level testing that DNR would then apply for large-scale production at the state's Deal Island hatchery, which had been constructed from an old oyster shucking plant. While DNR still operates the hatchery, oyster production there has been limited.

In the years after Agnes, with average and lower rainfall, natural oyster production had come back to the Bay and commercial watermen were harvesting public grounds again. Given Krantz's strong background in aquaculture, he and Meritt began working with Maryland leaseholders to try to get private aquaculture on a par with other areas on the east coast. "We took a lot of criticism from public fisherman," Meritt says, "that we were wasting money with the hatchery when so many wild oysters were available."

Sea Grant Extension

A door opened for Meritt when Krantz left Horn Point - "I had already taken over "by default," he says with a certain self-deprecation. Then another door opened when Tony Mazzaccaro, then head of Maryland Sea Grant Extension, proposed that he also work as an Extension shellfish specialist. Sea Grant Extension is a joint program with University of Maryland Extension.

What does a specialist do, Meritt is asked. "He talks to people, sometimes large numbers of them," he replies. "Before Sea Grant, I was in the hatchery or in the field. When I started working with Extension, I began doing outreach programs. I was now in the position of training people." Speaking in front of audiences was not comfortable, he says. For those who know his outspokenness, it may be difficult to believe that it still isn't. "It changed me a lot, maybe for the better."

"Extension or outreach is like coaching. You have some knowledge that the people you're dealing with don't have and you're trying to convince them that what you have is reasonable. You want to show them how to do it so that they're successful and things don't backfire on them."

"To be a good Extension agent, you have to be able to have a coaching mentality. I coach baseball. Every kid can't pitch," Meritt says. "I have to be able to tell that kid you're not a pitcher in such a way that I don't crush them while keeping their enthusiasm up. That's the same for Extension. Sometimes the best lessons that an Extension agent can give are the ones that lead people to not do what they wanted to do when they first came to see you. We've probably saved people more money by preventing them from doing what would not have worked had they not listened to us."

Part of his own Extension training was learning what aquaculturists were doing elsewhere. In 1986, Meritt traveled to the Pacific Northwest because he had heard about the hatchery-based industry there. "Before I went out there, I thought I knew how to grow oysters," he says. "I learned that I knew very little."

"Until then, I had dealt with scientists and management people where the public fishery was driving the boat. Every time you mentioned aquaculture in the Chesapeake, there were a thousand reasons people gave why it wouldn't work here. In the Northwest," Meritt says, "everybody was doing it! One couple had an old shed and they were growing a few million spat for sale. Companies were vertically integrated. This was private industry."

To Meritt, a large larval tank for setting spat was 1000 liters. "In some of those hatcheries, they have 25,000 or 40,000 liter larval tanks. They don't have one tank but a row of them, 15 or 20. At the time, we were setting maybe a million spat a year; they were doing ten times that every day!"

That experience gave Meritt a sense of what he needed to do. "Those estuaries are tiny compared to the Chesapeake but they're outproducing what we're doing using just a few hatcheries. Two or three produce all the eyed larvae that growers throughout the Northwest are using to set their own oysters. That thought has never escaped me."

The critics naturally said that "what they're doing out there won't work here." But the concept will, Meritt replied. "Let's make what they're doing work here." He and Maryland Sea Grant Extension Agent Don Webster spent a good deal of time on the road showing growers how they could purchase eyed larvae produced in a hatchery, set the seed oysters themselves on bagged or containerized shell and then plant them on leased grounds or grow them in cages or floats.

While Meritt's vision was of what the hatchery could contribute to the aquaculture industry, he began to think of what he could contribute to research that the hatchery was increasingly getting involved in. To do that effectively, he needed an advanced degree. In the mid-eighties he entered a doctoral program in the Marine-Estuarine-Environmental Science Program at the University of Maryland College Park. He received his Ph.D. in 1993, writing his dissertation on the effects that several parasites - the boring sponge, the mud worm and Dermo - have on oyster shell growth, phsyiological condition and mortality. It took a while, he says, again in self-deprecation, but unlike most graduate students in science, he did it part-time while running the hatchery and doing Extension programs.

Disease and Restoration

As part of the Oyster Roundtable Agreements a decade ago among watermen, aquaculturists, legislators, scientists, environmentalists and state agency representatives, only certifiably disease-free oyster spat can be planted in upriver bottom grounds. In effect, this means that naturally-produced seed cannot be moved into these sites because most of it would likely come from areas in which oysters are already infected with Dermo.

Since lower salinities are less conducive to Dermo and MSX, the aim of the upriver plantings, says Kennedy Paynter, has been to give oysters the chance to grow without the intense pressure of disease. In the last two years of near-drought conditions, higher salinities have penetrated much farther upriver than in years of average rainfall and some of these oysters have been under stress. Still, the upriver plantings are working in that oysters survive.

"Oysters planted way up in the Choptank in 1994 don't have disease yet," Meritt says. On the other hand, those planted in the lower Choptank that have been there for two years have been wiped out, probably from MSX. Meanwhile, oysters planted two years ago in Tangier Sound, where salinities are high, two years ago are beginning to get disease. "We're having success and failure - that's what makes things so difficult," Meritt says.

The problem remains - how to keep oysters alive long enough so they can breed and produce survivors to produce the next generation and the next and the next. This requires a solution to the disease problem. Some people believe that we're harvesting survivors and that we should leave them there so that they and their broods can continue to reproduce. But how many generations will it take before they build sufficient numbers of survivors, he asks? It has been 50 years since MSX first decimated populations in Delaware Bay, but despite the promise of natural selection favoring MSX survivors, the situation is no better off. Will it take another fifty years, or a hundred?

"We may have an oyster that evolved for a Chesapeake Bay ecosystem that no longer exists," Meritt says. The Bay today has parasites it has never seen before; it has problems of nutrient enrichment and low oxygen - if not an absence of oxygen - on many bottom grounds during the summer. In addition, the sediment problems are much more severe than in the past. All these stresses may be contributing to this oyster not being able to handle this Bay.

To establish sustainable reefs, oysters have to grow bigger or more oysters have to accrue on the reef faster than the reef is collapsing or getting suffocated by sedimentation. In the past, Meritt says, this was easier, because there was less runoff; there were also buffers of underwater grasses in some areas that could settle out sediment that would otherwise smother reefs, preventing new oysters from setting. As it is today, oysters are not recruiting new young very well and diseased adult oysters are growing so much more slowly.

Seed oysters in stainless steel cages - photo by Don Meritt    

Seed oysters in these stainless steel cages have hardened in near shore waters and are now ready to be transported for release onto restored reefs.

One approach to promoting sustainable reproduction has been to introduce disease-tolerant native oysters such as CROSBreeds and DEBYs that have been bred at the Virginia Institute of Marine Science and Rutgers' Haskins Shellfish Laboratory. These strains, originally developed for aquaculture where they are proving to be useful, are thought to offer some promise for revitalizing wild oyster stocks. The oysters are being tested at different sites in Chesapeake and Delaware bays and are also being grown by oyster gardeners in Maryland and Virginia.

The question remains, though, says Standish Allen of VIMS, whether they can survive disease pressure over the long term and be used on the immense scale it would likely take to jump start reproducing populations. Can they help to genetically rehabilitate wild populations? "It's possible," says Meritt. "Have we been able to do it?" he asks rhetorically. "No." There are many unknowns, for example, about their maintaining disease resistance, about their inbreeding and the consequent susceptibility to new disease, and about the dilution of their genes in mating with local oysters.

As for bringing in a new oyster, Crassostrea ariakensis, Meritt says it could be a useful tool in the face of disease. "If it is introduced, it probably will be successful in some places and not successful in others," he says, "and where it is successful, and by that I mean reproducing and spreading itself, it may re-establish what we often refer to as 'healthy oyster reefs.' They may not be identical in structure (although I feel they would be similar), but they should provide much of the same function as our native oyster." There might even be two species of reefs in some places. Is that bad, Meritt asks? "Maybe, maybe not. I think that if C. ariakensis was successful, even in a few locations, that we might begin to see some of the ecological side benefits that we all want out of oyster restoration."

What the future holds remains to be seen - research proposals, which he is part of, are in the works to further investigate C. ariakensis and disease-tolerant C. virginica strains. The increasing capacity to produce oyster spat in the new expanded hatchery will make it possible to explore innovative approaches for both aquaculture and self-sustaining populations. If we're successful, he says, we could begin to see a revitalized oyster industry in the Bay, probably different from the one that we have had historically. "And, with good fortune," he adds, "parts of the Bay ecosystem will be a beneficiary as well." But Meritt doesn't kid himself - these are big "ifs."


What Happens in the Hatchery?

Schematic of the oyster cycle - copyright by John North

In the Horn Point hatchery, eggs are first fertilized to produce larvae, which are fed an algae-rich diet and grown in tanks until they reach the "eyed" stage at two or three weeks of age. Physiologically, the process is punishing - even in a tank free of predators, only a small percent may survive to become spat. Tiny as they are, the older larvae (those ready to set) are distinguishable under a microscope. At this point they are separated from the other larvae and introduced into setting tanks containing clean, containerized oyster shells. The larvae then settle onto the surface of the shells, crawl around and when they find a suitable place, cement themselves to the shell. This transformation or metamorphosis from a free-swimming larva to a non-motile oyster is called settlement or setting and the oyster is now referred to as a spat. After a few days in the setting tanks that allow the newly-settled spat to grow and harden, the containerized shells are removed and placed in shallow water nurseries until final deployment to a planting site. Spat placed in the Bay take from one to several years, depending on environmental conditions, to grow to a harvestable size of three inches.

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