By MarylandReporter.com/Capital News Service, a student-powered news organization run by the University of Maryland Philip Merrill College of Journalism
Why did the blue crab cross the road on the Eastern Shore? We're not sure -- same for whether improving water quality will increase crabs and fish in the Bay. Bay Journal photo by Dave Harp
For decades, Chesapeake Bay cleanup efforts have been driven by a simple equation: Cleaner water equals more fish and shellfish.
The 1983 Chesapeake Bay Agreement, which launched the state-federal restoration effort, made that clear as it sought to reverse the Bay’s “historical decline in the living resources.” It would do so, the agreement said, by addressing pollution flowing into the Bay.
The living resources goal was reiterated in the next two cleanup agreements in 2000 and 2014, and the pollution goal aimed at making it happen has been refined to measurable targets for reducing nutrient pollution in the water.
But would achieving those goals actually result in more fish, crabs and oysters?
It’s complicated.
Bay scientists caution that the link between nutrient reductions and increased fish abundance is highly uncertain. In a report last year, they warned of a need for “grounding” the public’s expectations about the recovery of aquatic life even if cleanup goals are met.
In the May 2023 Comprehensive Evaluation of System Response (CESR) report, the Scientific and Technical Advisory Committee of the state-federal Chesapeake Bay Program cautioned that other factors — such as temperature, salinity, river flows and structural habitats — play important roles in determining fish abundance. Compared with those, the water quality role can be small.
“Considerable uncertainty,” they wrote, “will accompany any effort to predict how fish and shellfish populations respond to changes in water quality alone.”
Striped bass and some other fish species might benefit from reducing nutrient pollution in the Chesapeake Bay, but reducing it might not help others, such as menhaden.
At the same time, scientists who worked on the report are quick to say that doesn’t mean the Bay Program should walk away from its nutrient reduction commitments. Rather, they say, it points to the need to better understand the relative importance of water quality improvements and other factors, such as habitat restoration, in boosting aquatic populations.
That could inform efforts to balance spending on nutrient controls with other things, such as restoring wetlands or other habitat, to produce the greatest benefit for the widest variety of species.
“We’re really saying this is an evolution, not a revolution,” said Kenny Rose, a fisheries scientist with the University of Maryland Center for Environmental Science who was the lead author of the living resources section of the CESR report.
“And it’s what a large restoration program should be doing. It is moving along with changing information.”
The best place to figure that out, according to the report, is in shallow water areas that fringe the Bay and the tidal portions of tributaries that are disproportionately important for a wide range of creatures.
That recommendation has spurred recent interest within the Bay Program to focus increased pollution reduction and habitat restoration work on a handful of targeted nearshore areas.
The Challenge of Change
While not a revolution, that would be a significant change in direction — and it would also pose significant scientific challenges.
Historically, nutrient reduction actions have generally been aimed at improving the deepest parts of the upper Bay. That’s where water quality is the worst, and the theory is that improving deepwater conditions will improve other areas around the Bay as well.
But the CESR report warns that cleanup progress has been slow, the Bay has not responded as rapidly as expected, and that the deepwater goals may not be fully attainable.
It also pointed out that, when it comes to helping aquatic life, focusing most nutrient reduction efforts on deepwater areas could detract from other actions that would more directly help aquatic life.
A cluster of oysters grows just below the surface of Maryland’s Choptank River. Bay Journal photo by Dave Harp
That has triggered interest in creating a “tiered approach” to reducing nutrient pollution. In that approach, some shallow-water areas with a high potential to show results would get greater priority, even if their impact on deeper water would be relatively small.
Those nearshore areas would, in effect, become incubators for understanding how — and whether — alternate approaches to Bay restoration might produce better results for fish and shellfish.
That doesn’t mean that all emphasis would be removed from deepwater areas, said Lee McDonnell, chief of the science, analysis and implementation branch of the U.S. Environmental Protection Agency’s Chesapeake Bay Program Office.
Some focus on those areas is important because when oxygen disappears there, it triggers conditions that release nutrients stored in the sediment, making overall Bay water quality even worse.
“We can’t ignore the deep water [or] deep channel and say everybody’s going to focus on shallow water,” McDonnell said.
At the same time, he said, there is a public expectation that cleanup actions will result in tangible benefits.
“We’re asking for behavior change in people, and their expectation is that they should be able to see some kind of change and experience it,” McDonnell said. “There’s a much better chance of doing that in the shallow waters than in the deep trench.”
Shifting more resources to shallow water could slow the rate of progress in deepwater areas, but many scientists say the change is worth the trade-off if it results in quicker, more tangible benefits for aquatic life.
“This tiered implementation is not saying you’re taking your foot off the gas of the pursuit of a long-term goal,” said Penn State ecologist Denice Wardrop, one of the lead authors of the CESR report. “But at the pace we’re going, you need an interim goal because you’re going to be losing living resources on the way to the long-term goal. And you don’t need to.”
Finding the Balance
McDonnell, Wardrop, Rose and a handful of others have been meeting for months to figure out how to identify shallow areas to be prioritized — and how to assess whether their actions are making a difference. It’s a complex task.
Reducing nutrient loads in the Bay system have long been seen as a way to help living resources. The nutrients spur algae blooms that cloud the water and block sunlight from reaching underwater grass beds, which provide important habitat for juvenile fish and crabs, waterfowl and other species.
When the excess algae die, they decompose in a process that removes oxygen from the water, sometimes causing oxygen-starved “dead zones” that plague the deepest parts of the upper Bay each summer.
The nutrient reduction goals assigned to each Bay state and major tributary aim to improve those conditions, allowing more sunlight to reach underwater plants and largely eliminate dead zones.
That would certainly allow underwater grass meadows to expand and would benefit bottom-dwelling organisms, such as clams and worms, that can suffocate if oxygen levels get too low.
The increased oxygen is intended to help fish and crabs as well, but whether that would lead to greater abundance is unclear.
For one thing, those species can simply move if water conditions get bad. And many, such as striped bass, blue crabs, shad and others, spend most of their lives — or at least important life stages — outside the Chesapeake. Conditions in those areas often are more important in determining their abundance.
An eel swims in the shallows of Deer Creek, a tributary of the Susquehanna River. Bay Journal photo by Dave Harp
Further, reduced algae production isn’t always a good thing. While excess amounts can trigger poor oxygen levels, algae is also an important food, especially for fish in their early life stages, as well as for some adult fish, like menhaden, which are themselves an important food for larger fish and birds.
Indeed, a 2017 EPA study found that while species like striped bass and oysters might benefit from the improved water quality, the reduced algae production might hamper populations of others, such as Atlantic menhaden.
The CESR report also stated that “living resource abundance may eventually decrease as nutrient loads continue to decrease and [water quality goals] approach full attainment.”
“[There are] always going to be winners and losers,” said Tom Ihde, a researcher at Morgan State University’s Patuxent Environmental & Aquatic Research Laboratory, who also worked on the CESR report. “If you’re managing menhaden populations versus the blue crab, you’re concerned about very different things.”
Ihde has worked on complex computer models that try to tease out how various species respond to different variables. In a 2017 paper, he examined the responses of nearly 50 aquatic species to a variety of ecological changes.
He found that achieving the clean water goals only had a small impact on most species — though some, like blue crabs and white perch, showed benefits.
That influence was dwarfed by the impact of temperature increases. Achieving water quality goals does little to offset that problem for most species, he found.
That shouldn’t be totally surprising, Ihde said, because temperature affects everything in the system, such as growth rates, the timing of reproduction and food production.
“It’s not that the nutrient reductions are not having an effect,” Ihde said. “It is, and we’re seeing change. But it’s that temperature is much more of a change.”
It’s Never Just One Thing
Other factors — salinity, the amount of freshwater flowing into the Bay during spring spawning periods, fishing pressure, disease and loss of structural habitats — are also important in influencing species abundance.
A recent Bay Program report looked at the habitats of forage fish, which are small species eaten by larger fish and birds. The researchers found that shoreline hardening played an important role in predicting their abundance. The most sensitive forage species go away when just 10% of an area’s shoreline is covered by bulkheads or rip-rap. And many comparatively tolerant species disappear when that amount reaches 30%.
The CESR report noted that benefits of water quality improvements “will be modest” if such factors are limiting populations.
But, it said, pairing water quality work with other actions — restoring wetlands, replacing hardened shorelines with living shorelines or building oyster reefs — might yield better overall results.
There is some evidence of that. In recent years, state and federal agencies have worked to restore large oyster reefs in 11 Bay tributaries.
Monitoring has shown that underwater grasses are rebounding in areas near the reefs, very likely a result of oysters filtering the water. Other studies have found that oyster reefs help remove nutrients from the water.
“We feel pretty confident that doing large-scale oyster restoration leads to ecological benefits,” said Bruce Vogt of the National Oceanic and Atmospheric Administration Chesapeake Bay Office. “We have very clear evidence that the oyster reefs are cleaning the water and produce better clarity.”
Fish abundance is also higher near the reefs, though Vogt said it is less clear whether the reefs are boosting fish reproduction or merely attracting fish from other areas.
That is the type of question that scientists say could be cleared up by targeting some shallow water areas for more intense work and monitoring the results.
Still, understanding impacts in a given area — and predicting whether positive signs in one area would be repeated in others — is no easy task in a system as large and complex as the Chesapeake.
“Not all oyster habitats are equal, and not all seagrass habitats are equal,” said Mark Monaco, a senior scientist with NOAA’s
National Centers for Coastal Ocean Science and an author of the CESR report. “How do those relationships hold up across the Bay in specific areas? And would an enhancement in habitat restoration actually move the dial in a particular area?”
Getting to a Tipping Point
The good news, Monaco said, is that a lot of data is available. Fish surveys and studies have taken place in the Bay for decades. They’ve never really been integrated with information on habitats, water quality and other variables that can impact fish, but that work has begun.
It will take at least two years to glean needed information from that data and identify shallow water areas for emphasis, according to those working on the process.
And there are a lot of basic details to work out along the way: What does “shallow water” actually mean? Is that two feet deep or six feet deep? What species and what life stages should be included in an analysis? How big of an area would be targeted?
The hope, said McDonnell of the EPA Bay Program Office, is to find shallow areas near an ecological “tipping point” where a realistic amount of action can turn an area of poor habitat into fair habitat, or a fair area into a good area, and produce faster improvements for the species that live there.
“If we’re going to have this tiered implementation, it has to be grounded in science,” he said. “If we’re going to do something different than we’re doing now, there ought to be a reason for it. I’m hoping this is our good reason.”
Karl Blankenship is editor-at-large of the Bay Journal. You can reach him at kblankenship@bayjournal.com.
