Hidden under the surface of Maryland’s Harris Creek is what looks like — at least for now — one of the Bay’s greatest successes. It is, unfortunately, one that hardly anyone can see.

Work completed through the end of last year restored 188.6 acres of oyster reef habitat on the bottom of the Choptank River tributary, most of it in places more than 6 feet deep.

That’s already made it more than twice the size of any sanctuary-based oyster restoration previously undertaken around the Bay. Yet another 85 acres of new reef construction is under contract — some is already under way — for this year.

By the time work is wrapped up in 2015, the project will cover roughly 350 acres, and those areas will have received nearly 2 billion baby oysters, or “spat.” Unknown numbers of naturally produced oysters also landed on the site during an unusually large 2012 oyster spawn.

“There are hundreds of millions more oysters than when we started in Harris Creek,” said Mike Naylor, who oversees the Maryland Department of Natural Resources Shellfish Program. “When we revisit the areas that we’ve planted, they are absolutely thriving.”

The work is largely being carried out by the DNR, federal agencies and the nonprofit Oyster Recovery Partnership. But when construction is done, the most anxious part of the project will begin — waiting to see whether all of those numbers will add up to long-term success.

“The real question is, will it sustain itself?” Naylor asked. “We can put them out there, but will they sustain themselves or will they fall back to pre-construction levels at some point in the future?”

“It’s going to be a long time before someone raises a flag and says Harris Creek is restored.”

Harris Creek represents a new approach to oyster restoration. Whereas most past projects were often only a few acres in size, the new approach seeks to restore — and repopulate — large tracts of oyster habitat within small tributaries. The hope is that they will become self-sustaining, gradually expanding both their numbers — and reef habitat — over time.

And, plans are under way to kick off large-scale projects in four more tributaries, with work beginning in most of them this year. They include:

≈ The Little Choptank River, where the Maryland DNR expects to construct about 30 acres or reef this year as part of a project that will likely cover 200–400 acres in coming years.

≈ The Tred Avon, a Choptank tributary near Harris Creek, where the Army Corps of Engineers Baltimore District this year expects to construct 25 acres of reef as part of a project expected to ultimately cover about 200 acres.

≈ The Piankatank River, just south of the Rappahannock, where The Nature Conservancy is partnering with the Virginia Marine Resources Commission, National Oceanic and Atmospheric Administration and Army Corps of Engineers Norfolk District and others to construct 20 acres. It’s the first part of a project that may eventually cover several hundred acres in the river.

≈ The Lafayette River, a tributary of the Elizabeth River in Norfolk, where community and environmental groups supported by the NOAA Chesapeake Bay Office will continue planting small reefs this year. But those groups, and the Corps Norfolk District, are planning a larger project that will likely begin major construction next year that could eventually cover more than 200 acres.

Cumulatively, those projects will eventually total many hundreds of acres — potentially more than a thousand — beyond what is being built in Harris Creek.

Self-sustaining populations

If they are all successful, it would be a big step toward restoring self-sustaining oyster populations in 10 tributaries by 2025, the goal set in the draft Chesapeake Bay Watershed Agreement.

It would also represent a huge investment: The cost of Harris Creek alone will approach $30 million, and the combined cost of all the other projects is in the tens of millions of dollars.

“When you start measuring the economic and natural benefits, it looks like a good investment, but the up-front costs are expensive,” said Andy Lacatell, of The Nature Conservancy, which received a $500,000 grant from the Mary Morton Parsons Foundation to help launch the Piankatank project.

Lacatell noted that oysters help clear the water, remove algae and build habitat used by fish, clams and other aquatic dwellers. “Assuming you have a successful reef, the investment is a good one.”

Past restoration projects were often only a few acres in size. While many showed initial signs of success, those small reefs simply did not provide a large enough area upon which oyster larvae could settle; many larvae were just swept away into areas with muddy bottoms, where they died. The reefs also succumbed over time because of disease, sedimentation, poor water quality, legal harvest and poaching — or a combination of those factors.

The new large-scale strategy seeks to rehabilitate the majority of remaining potential reef habitat in an entire tributary with the hope of reaching a tipping point where oyster populations are not only self-sustaining, but also maintaining and expanding their reefs as well as influencing local water and habitat quality. The guiding strategy, developed by agencies and scientists in recent years, also calls for the reefs to be protected in sanctuaries with the hope that, left alone, the oysters over generations will develop resistance to the diseases that have devastated the Bay’s oyster population.

There are signs the strategy is working. They are coming from Virginia’s Lynnhaven River, near the mouth of the Bay.

Though not technically a sanctuary, the Lynnhaven for decades was off-limits to fishing because of high bacteria levels in the water. Over the years, Lynnhaven Now and other local groups began putting reefs in the water, a process that was accelerated in the mid-2000s when the Corps Norfolk District began a $5 million investment in oyster restoration in the river, building 58 acres of reefs.

That ultimately brought the reef acreage in the Lynnhaven to 63 acres.

Because of the river’s small size, that may be enough for it to earn the title of being the Bay’s first “restored” tributary under criteria established by scientists two years ago.

Under that criteria, at least 50 percent of the currently restorable bottom has to be returned to oyster habitat. Six years after the project is completed, the reefs need to have a minimum of 15 oysters per square meter, with 50 being the target. The oyster population has to consist of at least two year classes, so the goal can’t be met on the basis of a single good spat set. And, the reef area has to be stable or increasing in size.

Those oyster densities are modest compared with historic reefs in the Bay, but they represent the best estimates by scientists of the minimal oyster population needed to be self-sustaining — enough oysters in close proximity to both improve the odds of reproductive success and to maintain itself— and gradually expand reef habitat.

“We feel that the recruitment in the Lynnhaven has gone up phenomenally,” said Susan Conner, chief of the Environmental Analyses Section of the Corps’ Norfolk District. “That is a reason we are feeling pretty confident that it is likely a successfully restored tributary.”

But, she stopped short of declaring it restored. “I think that is more than a Corps decision,” she said. “The stakeholders in the tributary need to agree on that.”

Better site selection

On Harris Creek, valuable lessons have been learned, too. The creek has been “seeded” with 1.2 billion oysters reared at the University of Maryland Horn Point Lab. There, spat is produced at a hatchery then allowed to settle onto oyster shells before being taken for planting at Harris Creek.

In the past, spat on shell was placed on suitable bottom identified using side-scan sonar. On Harris Creek, though, divers were used to confirm the suitability of the bottom before the spat on shell was placed. Normally, spat survival is about 15 percent. But on Harris Creek, 37 percent of planted spat survived in 2012, and 35 percent in 2013 — more than twice what was expected.

Officials believe the new technique is likely responsible. If so, that could reduce the cost for Harris Creek and future projects, especially in Maryland where restoration is highly dependent on the use of hatchery oysters.

“We are using science for site selection better than we have in the past,” said Stephanie Westby, oyster project coordinator with NOAA’s Chesapeake Bay Office.

Still, there are many hurdles remaining for oyster restoration in both states. Perhaps most significantly, there is no guaranteed source of money — state or federal — for future projects, or to even complete the ones being started this year.

“The results we’ve seen have been very, very promising, and we are using good techniques, but if the funding dries up, that would make it difficult,” Westby said.

Much of the cost goes into reef construction, which requires large amounts of oyster shell, the supply of which is limited and increasingly expensive. Maryland recently began importing fossil oyster shell from Florida to use in reef construction, and both Maryland and Virginia are experimenting with alternate substrates and construction techniques.

Another issue is that in Virginia there are relatively few large sanctuaries available for reef construction. That’s one reason the Lafayette is an attractive restoration site — it’s not a designated sanctuary, but the urban waterway is so polluted the oysters can’t be harvested.

It’s also been the site of several small-scale projects supported by the Elizabeth River Project and the Chesapeake Bay Foundation that have shown some sign of success. And scientists were pleasantly surprised in March when they discovered several oyster reefs — left undisturbed for decades — were thriving in the river. Some oysters had grown as large as a man’s hand.

“There are some prime oyster reefs that haven’t been harmed, probably because the tributary has hasn’t been open for harvest,” Conner said.

But the Piankatank is different. While it includes sanctuaries, it also includes areas that allow for harvests of oyster “seed,” which is transplanted to other rivers. It also has areas of leased bottom upstream of the restoration sites.

The Piankatank plan will need to ensure that a sizable patchwork of suitable habitat can be protected to meet restoration goals. “Anytime we want to do a restoration project, securing that bottom area is a hurdle both for the Corps and even for smaller groups,” Conner said.

Even where oysters are protected by sanctuaries, poaching remains a concern, although both states have been ramping up enforcement efforts. This summer, 18 acres of an 85-acre network of reefs in Virginia’s Great Wicomico River are being rehabilitated in part because a portion of it was poached, even though it was in a sanctuary. (Until the Harris Creek project, that was the largest restoration effort in the Bay.)

Maryland has set aside entire tributaries as sanctuaries, but putting together projects that cover at least 50 percent of the available habitat is still a challenge. Large chunks of tributaries are off-limits to restoration: Work is prohibited in, or buffers required around, navigation channels, shallow water areas used by boats, docks, marinas and navigational buoys.

Not only has much of the historic reef habitat been lost in the mud, but much of what remains is not usable.

“It can become substantial,” said Angela Sowers, of the Baltimore Corps’ planning division. “Fortunately, in Harris Creek, we had plenty of areas to work in. In other areas, it might be an issue where we can’t reach our restoration goals because there are just too many conflicting uses.”

Disease mortality is always a concern. The oyster diseases MSX and Dermo thrive in high salinities and always challenge oysters in Virginia, though scientists say they are starting to see signs of resistance. High salinities also promote reproduction, though, so lost oysters on Virginia reefs are more likely to be replaced.

But cownose rays, which can be voracious oyster predators, are more common in Virginia, as are reef-fouling organisms.

Disease pressure is less severe in Maryland, but mortality can be a serious problem in times of drought when salinities rise and disease intensifies. Because reproduction is more sporadic, lost oysters may not be as readily replaced after a die-off.

On Harris Creek, monitoring has found varying levels of Dermo infection, with infection rates reaching 100 percent on some reefs established in 2012. But the intensity of infections in individual oysters has been low, and so has disease mortality.

That situation could change if salinities increase with dry conditions. Naylor said it’s inevitable that the reefs will eventually be hit with substantial disease mortality. But, he added, “it’s not a bad thing to have that disease pressure in the sanctuaries. One of the goals of the sanctuaries is to facilitate disease resistance by allowing disease survivors to continue to live and reproduce instead of being harvested.”

Multi-decade task for Bay

As big as the current restoration projects are, officials caution that restoring small tributaries is a long way from restoring the greatly depleted oyster populations of the Chesapeake.

Oyster bars were once a dominant feature of the Bay and its tidal tributaries, covering around 450,000 acres in the late 1800s. But overharvesting, disease and poor water quality caused oyster populations to plummet to 1 percent or less of their historic levels. Gone, too, is most of their habitat. Historic reefs were dredged away by harvesters, buried by sediment or the shells simply dissolved over time.

In Maryland alone, the amount of suitable oyster bar habitat has declined 80 percent in just the last 25 years, according to the DNR.

All of the oyster projects under way combined, when completed, would restore less than one-quarter of 1 percent of that historic oyster habitat.

“We have to keep our expectations realistic,” Naylor said. “We do expect to see some pretty significant ecological changes within the systems that are receiving a lot of attention. But to think you are fixing the Bay with this is a stretch.”

A substantial rebound in wild Chesapeake oysters would be a multi-decade task that would rely on oysters building disease-resistance and slowly reclaiming lost habitats with new reefs. Nothing, after all, builds oyster habitat better than an oyster.

But lessons learned in Harris Creek and other projects may help nudge that process forward in places around the Bay.

“So far, it’s been a really positive project and has gone as well — if not better — than expected,” Sowers said. “It’s just too bad everything is underwater where you can’t see it.”