Heavy rain, climate change mean trouble for oysters
As shucking season begins, the forecast for Chesapeake Bay oysters is worrisome. Record rainfall has made the water less salty — and oysters need salt to thrive. Harvesters may find fewer of them this year, and many will be too small.
And the impact on the struggling shellfish could go well beyond this winter. If climate change means spring and summer deluges become more common, that will be one more obstacle to the effort to rebuild the bay’s once-thriving oyster population.
Jim Mullin, president of the Maryland Oystermen’s Association, said he’s afraid increased rainfall could set back years of work to help oysters.
“You can plant as many oysters in the bay as you want, but they’re not going to survive if this keeps up,” he said. “What if this happens again? It’s an eye-opener.”
If Hollywood Oyster Co.’s current crop is any indication, this year has indeed been a challenging one for oyster growth. Owner Tal Petty says the oyster farm off the Patuxent River in St. Mary’s County usually sees a “bump” in oysters’ size in the spring, once waters warm, and again in the fall. But this year, there was no spring bump. “The conditions were there to grow, but the salt wasn’t there,” Petty said. “I’ve just never experienced that in my 20 years.”
Increased rainfall and other issues associated with climate change influence big decisions Maryland must make about how to manage its oyster population. Rising and increasingly acidic oceans also could affect the way the shellfish fare in the long run.
A long-awaited report detailing the state of the oyster fishery is due to state lawmakers this month. It could restart
paused discussions about whether watermen should be given periodic access to oyster sanctuaries — relatively robust reefs that have for years been off limits to harvest. Under Gov. Larry Hogan, the state has worked to balance commerce and conservation.
The debate is a contentious one because with oysters, more is at stake than the species itself. The mollusk naturally filters impurities from the water. So the recovery of the oyster population means recovery of the bay.
Allison Colden, Maryland fisheries scientist for the Chesapeake Bay Foundation, said that if heavy rain becomes more routine and harms oyster reproduction, the job of managing oyster harvests would become more difficult.
“The number you can take out continues to get smaller and smaller if you want to sustain the population,” she said.
Too much rain
Much of Maryland has experienced 60 inches of precipitation so far in 2018 — a foot and a half more than what falls in a typical calendar year. The rain has kept the brackish waters of many Chesapeake tributaries fresher and less salty than normal. Oysters have evolved to develop some tolerance of fresh water, but need saltwater to grow and reproduce.
Because much of the rain came during the spring and summer months, when oysters spawn and larvae drift in search of a reef, there may have been virtually zero natural oyster reproduction this year.
That could be a setback watermen feel for years to come — it takes two or three years for baby oysters to grow to legal market size of 3 inches.
The rain also slowed production on oyster farms, limited the opportunities to seed reefs with lab-grown oysters, and likely killed some mature oysters in upper reaches of the bay.
Oystering is a $90 million industry in Maryland, and a $200 million one down in Virginia’s relatively saltier waters. Millions of dollars of federal, state and private money are invested in oyster plantings and reef construction each year.
Oysters that live in the Chesapeake Bay can survive in a range of conditions, but a shock of fresh water — especially one that lingers amid frequent heavy rains — can be too much for them to handle. Too much salt, and oyster cells shrivel up and die; too little and the cells become engorged with water.
Adult oysters can close their shells for self-preservation when necessary, but can only go without food for so long. Larvae have an even narrower tolerance for swings in salinity.
Sapping energy
And the more energy they have to put toward survival, the less they grow or reproduce.
Waterman Robby Witt said he hasn’t noticed much oyster growth in the waters near his dock in southern Anne Arundel County. And there was so little salt in the Rhode River this summer, it was impossible to plant oyster spat grown in tanks onto reefs, he said. They would have just died.
Scientists say they’re confident climate change will have a long-term effect on oysters’ future in the bay — they just don’t know what it will be.
Aside from predictions of more frequent and more intense downpours, oysters are facing the threat of ocean acidification as rising carbon dioxide levels in the air create more carbonic acid in the water. That could limit their ability to grow shells.
And then there is sea level rise. Melting ice and warming waters could push the Chesapeake as much as 2 feet higher by 2050. That could send more saltwater up the bay, actually promoting oyster growth and potentially spreading their prime habitat farther up the estuary. Yet warmer, saltier waters could also bring a resurgence of the oyster-killing diseases MSX and Dermo.
“There’s sort of opposing forces out there that, on the one hand, could provide better and more habitat, and on the other could be more challenging,” Colden said. “It’s hard to say at this point how the oysters will fare in the long term.”
But there’s no question that more intense bursts of fresh water would be difficult for oysters to handle.
Don Boesch, a professor at the University of Maryland Center for Environmental Science and the institution’s president from 1990 until last year, said oysters in at least some parts of the bay could have to weather big environmental changes.
“It may be that some parts of the bay now conducive to growing oysters, either on natural reefs or in aquaculture, may be less so,” he said.
‘Secure future?’
After too many dry years in the 1980s and 1990s, the problem for Chesapeake oysters was, if anything, too much salinity. Diseases ravaged populations in saltier waters.
That forced some adjustments to oyster management strategies. It shifted much of the restoration work to fresher upstream waters, where scientists hoped sanctuaries that are off limits to watermen would allow the species to grow away from the threat of disease. In sanctuaries where disease killed off large numbers of oysters, they hoped the survivors would meanwhile breed disease resistance into the population.
If 2018 signals a wet weather trend, that could force a different set of strategies, said Chris Judy, manager of Maryland’s oyster fishery for the state Department of Natural Resources.
While he said it’s too early to know if that will be the case, he agreed fresher waters could be a new threat to the mollusks’ survival.
“Watermen are looking ahead this way — what do we need to do to have a more secure future?” Judy said.
It could mean that the locations where oyster spat and shells are planted have to change, or that expectations of future oyster growth and reproduction have to change, he said. And what if instead of three years before spat grow to market size, it takes four? That could be possible, too, Judy said.
The questions come as policymakers and environmental groups prepare to take their closest look at the bay’s oyster population in years. Amid debate about whether it had recovered enough for some sanctuaries to be reopened to harvest, state lawmakers in 2016 ordered what is known as a stock assessment — a study of the population more detailed than the annual surveys.
General Assembly’s role
When talk of sanctuary harvesting continued last year, the General Assembly passed a law outlawing the practice until the stock assessment is finished. The report is expected to be unveiled later this month, and formally handed over to the legislature in December.
Colden said the bay foundation hopes the study helps inform oyster management strategies that ensure the population can withstand swings from any environmental pressures, be it surges of rainfall or acidifying waters. Watermen have meanwhile been wary of the report from its genesis, expecting it to lead to more restrictions on them.
It’s too early to know what the takeaways will be, or even to be certain what the risks are, Judy said. But it’s important to be cautious and aware, he said. And if new strategies are needed, he said, it wouldn’t be the first time.
“We’ve adapted many times,” he said. “This would just be another instance of adapting to a changing environment.”