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Oyster Sanctuaries: An Ecological Approach to Restoration

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A scientific consensus calls for a new concept of oyster management, one that recognizes the vital ecological function of oyster reefs for the health of the Bay.

By Merrill Leffler

Once the Chesapeake Bay teemed with oysters – oysters so large and plentiful that early visitors returned to the Old World astonished by what they had seen. In the words of Francis Louis Michel, after a visit to the Bay in 1701, "The abundance of oysters is incredible. There are whole banks of them so that the ships must avoid them. They surpass those in England by far in size, indeed they are four times as large."

By the end of the nineteenth century, those "banks" of oysters had fallen to the iron teeth of oyster dredges, many pulled by large schooners come down from New England to harvest the Chesapeake’s "white gold." Scientists and others who had witnessed the destruction of the Bay’s oyster reefs began to warn that without more careful management, oyster populations and the fishery they support were headed for ruin.

As early as 1891, John Hopkins biologist William K. Brooks blamed what he saw as the coming failure of Maryland’s oyster fishery on "improvidence and mismanagement and blind confidence." Brooks, one of the "few greatest of American zoologists" according to an article in Science magazine in 1908, expressed anger and dismay, arguing that soon there would be no oysters left "to replenish the beds."

The failure of the Bay’s oyster fishery has taken longer than Brooks, and those scientists who followed, expected – a tribute perhaps to the oyster’s resilience and fecundity. Nevertheless, failure it has been. Harvests – one measure of the state of the oyster – are today less than 20 percent of what they were twenty years ago and only a few percent of what they were at the beginning of the century.

It is against this backdrop that scientists in Maryland and Virginia have released a scientific consensus, under the auspices of the Chesapeake Research Consortium (CRC), setting out specific actions that could guide long-term restoration of oyster populations to the Bay.

"I think this is a breakout opportunity for getting oyster management on a science-based track."

The consensus calls for a new concept of oyster management, one that recognizes the vital ecological function of oysters and oyster reefs for the health of the Bay. By constructing substantial reef habitats and properly managing them, the scientists contend, there is a better chance to develop a sustainable oyster fishery, one that does not depend on public subsidies to keep it going.

At the heart of the consensus, which grew out of a recent meeting in Wachapreague, Virginia, is the recommendation to reestablish oyster reefs that are high above the bottom – living structures that are natural to the Bay ecosystem but have been nearly eliminated. These reefs must be protected in sanctuaries, the scientists say, off-limits to harvesting.

Because adult oysters release eggs and sperm directly into the water, depending on chance contact for fertilization, the proximity of adults is crucial to the success of new larvae. The billions of eggs and sperm released from large oyster reefs are likely to lead to much higher percentages of fertilized young than eggs and sperm released on small reefs or from oysters that are scattered along the bottom, as is the case in many areas of the Bay.

Restored reefs, high above the bottom and exempt from harvesting, would be continual sources of larvae says Eugene Burreson, chair of the CRC scientific consensus group and Director of Research and Advisory Services at the Virginia Institute of Marine Science (VIMS). The free-swimming larvae would likely ripple out into non-sanctuary habitats where they would set on shell and, once grown, could then be harvested. In this way, adds Victor Kennedy, a biologist at the University of Maryland Center for Environmental Science (UMCES), it is conceivable that enough protected reefs could eventually invigorate the commercial fishery by becoming a sustainable provider of seed oysters.

Science & Oyster Management

Historically, oyster policy and management in Maryland and Virginia has focused on one goal, the support of the commercial oyster fishery. Even Brooks based his arguments for conservation in economic terms. In claiming that "our method of managing the oyster industry has been a failure," he wrote that "it has yielded on the average some ten million bushels of oysters annually from grounds which are capable of yielding five hundred million bushels each year."

The argument for restoration no longer rests on the commercial fishery alone.

In the last ten years, we have begun to appreciate the significant role oysters play in filtering algae from the water – in so doing, they remove nutrients and help improve water quality. A paper by UMCES scientist Roger Newell in 1987 made the dramatic point that oyster populations at the beginning of the century could have filtered the entire Chesapeake in several days, while the populations remaining at the end of the 20th century would take more than a year. Only more recently, however, have we begun to appreciate the extent to which healthy oyster reefs are critical habitat – not only for oysters but for the myriad of other organisms that healthy populations of crabs and fish depend on.

It is for such reasons that the scientists who met in Wachapreague argue that "restoration must not be to manage oysters just to support a fishery, but they must be restored and managed for their ecological value, in such a way that a sustainable fishery can exist."

In a recent study of the history of oyster management, Johns Hopkins researcher Christine Keiner concluded, "The involvement of Brooks and other researchers in the Maryland oyster culture debate illustrates the weak role of scientific authority in influencing public policy making." Active engagement in trying to influence policy, she writes, "was thwarted by grassroots resource-use groups, primarily Chesapeake oystermen."

Are today’s scientists anymore likely to be successful than they have been over the last hundred years?

Some are skeptical. One says privately that state management equates the public fishery as belonging to watermen – but notes that the rest of us are the public as well.

Don Boesch, UMCES President, is actively optimistic. "I think this is a breakout opportunity for getting oyster management on a science-based track," he says. "While I may be an eternal optimist, there are key differences between former times and now."

To begin with, says Boesch, there is the depressed state of oyster populations in the Bay – they are at all-time lows and at the mercy of parasitic diseases, MSX and Dermo in particular. While oysters have had improved survival in these last few years, that survival appears to be the result of "wet" seasons, heavy spring and summer precipitation which has kept water salinity low and disease pressure low as well. This year’s drought conditions and high salinities, many scientists predict, are likely to favor disease, bringing more dead and dying oysters.

But a second key phenomenon, Boesch points out, could have surprising political influence on the way that both Maryland and Virginia manage oysters. That phenomenon is the expanding number of oyster gardeners, more than a thousand citizens as well as school age children, who have been participating in programs to grow oysters in floating racks for restoration efforts. Organized by VIMS in Virginia and the Chesapeake Bay Foundation in cooperation with Maryland Sea Grant Extension and UMCES in Maryland, oyster gardening is not merely teaching citizens to grow oysters but is educating them about the importance of oysters and oyster reefs as critical habitat.

There is a third reason for the potential influence of this scientific consensus. The impetus for the consensus itself came from a meeting that Bay scientists had with the secretaries of Natural Resources in Maryland and Virginia. "Typically, management agencies in Maryland and Virginia go about their efforts separately," says Eugene Burreson. He felt that scientists should be able to come up with Bay-wide goals and strategies, "and that we could reach a consensus on what should be done based on scientific data and principles." If we could do that, Burreson says, "then we could go to the managers with our consensus." Virginia Natural Resources head John Paul Woodley, Jr., and former Maryland DNR head John Griffin agreed.

Reefs Are Essential Habitat

That left to their own devices, oysters will form large reefs should come as no surprise. It is well-known from Colonial writing that oyster "rocks" were often hazards to navigation, though early on harvesting began reducing the height of reefs. Some have argued that, initially, harvesting helped to increase natural production by spreading oysters more widely; if so, advantage slowly turned to disadvantage as land runoff increased – the consequence of clearing forests for agriculture – and over the years began to smother many of the decimated reefs.

In the last twenty years, parasitic disease, MSX and Dermo especially, have wreaked havoc on Bay oysters, killing many before they reach harvestable size (see www.mdsg.umd. edu/oysters/ for more on the history of oyster disease). But the success of disease may, to some extent, be a consequence of resource management practices. For example, state programs for moving oysters from seed grounds onto other public grounds each year have inadvertently spread infected oysters throughout the Chesapeake. Furthermore, harvesting itself removes oysters that have survived disease pressure – therefore removing as well their inherent resistance and the resistance they might pass on to their progeny.

In a scathing conclusion to The Precarious State of the Chesapeake Public Oyster Resource, William Hargis and Dexter Haven, both of whom are Emeritus Professors of Marine Science at VIMS, write, "the principal causes of the long-term decline in Chesapeake Bay oyster populations on the public grounds are neither disease nor pollution but persistent overharvesting and its consequent impact on broodstock size and composition, negative genetic impact, and associated habitat destruction."

From the perspective of traditional management of the public oyster grounds in the Chesapeake, the call by scientists for permanent reef sanctuaries on public grounds that have historically received natural spat set (the settlement of free-swimming larval oysters) is probably the most radical. These reefs must rise "substantially" from the seafloor, the scientists say, to at least one-half the water depth. While shell may be planted around these reefs to enhance the setting of new oysters, perhaps for future harvest, the reefs themselves must be off-limits to commercial harvest, they say.

The success of oyster reefs ecologically and for the fishery will depend on locating large reefs in protected sanctuaries. They will provide enhanced habitats and, in the long term, more oysters. There is scientific and field evidence to support their claims.

In an extensive review of research on the role of oyster reefs as habitat, Loren Coen of the South Carolina Department of Natural Resources, Mark Luckenback of VIMS and Denise Breitburg of the Academy of Natural Sciences Estuarine Research Center conclude that the construction of reefs that provide "adequate vertical relief" and "the establishment of broodstock sanctuaries protected from harvesting pressure are important for restoring oyster populations."

James Wesson, Chief of the Conservation and Replenishment Division of the Virginia Marine Resources Commission (VMRC), has overseen the building of 15 reefs since 1993. "The monitoring results have clearly demonstrated the value of the reef structure in ways that should have been obvious in the beginning," he writes in a report to the Virginia General Assembly. Reef structures protect young oysters from predators; oysters also grow faster and spawn more effectively when off the bottom. In comparing spat set for low-lying oyster bottom and for a constructed reef, Wesson found striking differences: 11 spat per meter on the bottom compared with 100 spat per meter on the reef.

The Great Wicomico is a "trap" estuary, Wesson points out, "where many oyster larvae are retained in the river." In 1996, VMRC deployed 2,000 bushels of oysters from Tangier Sound on the newly-constructed reef. In 1997, they found that spat set in the Great Wicomico increased remarkably, up to five miles from the reef. "We surmise," he writes, "that aggregation of these oysters on the reef resulted in much improved fertilization rates."

In Maryland, Kennedy Paynter, a researcher at the UMCES Chesapeake Biological Laboratory and UM College Park, has been working with the state DNR and Army Corps of Engineers in comparing constructed reef habitats with "flat habitats," the more-scattered remains of natural reefs. With 15 sites in the Choptank, Patuxent and Chester rivers, Paynter has not found differences in spat set between the two. However, the Maryland and Virginia reefs are not comparable, Paynter says: the Virginia oyster reefs are large vertical structures in which some of the peaks are exposed at low tide; the Maryland reefs are smaller mounds of oysters. "What we need to do," he says, "is construct reef structures that are more vertical, say 50 percent of water depth, so that in 20 feet of water, for example, the reefs will be 10 feet high."

Even small reefs appear more productive than low-lying shell, however. "What is staggeringly different between the flat habitats and our constructed reefs," says Paynter with evident excitement, "is the vibrant nature of the reefs." Extensive underwater videotaping of both habitats in Maryland waters give dramatic evidence. "The video shows an immense diversity of animals using the small reef habitats, from barnacles and anemones to grass shrimp to perch and crabs. Unlike oysters on the remnants of natural reefs which lie flat on the bottom," Paynter points out, "oysters on the constructed reefs are growing vertically. They look like 8 or 10-inch flower pots sprouting up into the water." Paynter’s observations complement studies that Coen, Luckenback and Breitburg summarize in their review article: "oyster reef communities along the Atlantic and Gulf coasts are highly diverse," they write, "and include numerous species rare or absent in adjacent soft-bottom habitats."

The success of oyster reefs ecologically and for the fishery will depend on locating large reefs in protected sanctuaries

Building reefs will be no small undertaking and will take a sizeable commitment by government agencies and the private sector. An idea of the costs can be gleaned from estimates by the Virginia Department of Environmental Quality and VMRC to construct sanctuary reefs as part of the newly-formed Virginia Oyster Heritage Program. The cost for constructing eight one-acre sanctuary reefs in the Rappahannock River – each 8- to 10-feet high and surrounded by 25 acres of 10-inch deep oyster shell – is estimated at $380,000 per site.

The bi-state Chesapeake Bay Aquatic Reef Plan and the Oyster Fishery Management Plan of 1994 called for restoring 5,000 acres of three-dimensional oyster reef habitat by the year 2000. While Maryland and Virginia have gotten started, it is only a beginning – with more than 400,000 acres of public ground in the Chesapeake, there are numbers of questions that need answers. For instance, what are realizable oyster restoration goals over the next decade? What is the potential effect on habitat and fisheries? How many sanctuaries and reefs will it take? What size should they be? How far apart? Because harvests have been so low, there is hardly enough shell to meet the restoration needs – what alternative materials are available?

And yet, while these difficult questions remain, decades of research have accumulated a wealth of information, on potential reef materials, on predation and disease, on growth and reproduction. As Don Boesch and Eugene Burreson say, the time for a strong link between science and management has never been better.

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This page was last modified May 21, 2004

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