By FRANK CARINI/ecoRI News staff
Nearly 40 million clams were harvested from Narragansett Bay in
2012, according to Rhode Island Sea Grant.
Estimates of clams in the bay are used to set fishing limits. In Rhode Island,
commercial shellfishermen use a bull rake for harvesting clams. (R.I. Sea
Grant)
Shellfish are arguably one of southern New England’s most valuable
natural resources. Like the region’s many popular beaches, the area’s quahogs,
oysters, lobsters and clams attract tourists. Clamming, as much as sunbathing,
is a local summertime ritual.
Ocean acidification,
however, a byproduct of the planet’s changing climate, is threatening shellfish
and the industries they support. Studies have found that more acidic salt
waters make it more difficult for oysters, mussels, scallops and other shelled
mollusks to develop their hardened protection.
Shellfish rely on aragonite, a naturally occurring form of calcium
carbonate, to generate their shells. Increased ocean acidity, however, means
less aragonite, forcing mollusks to expend more energy to build shells and less
on reproduction and survival.
Mark Gibson, deputy chief of marine fisheries at the Rhode Island
Department of Environmental Management, told the Providence Journal last
year that ocean acidification is a “significant threat” to local fisheries.
In fact, a study published last year said the Ocean State’s
shellfish populations are among the most vulnerable in the United States to the
impacts of acidification.
Ocean acidification — a change in pH accelerated by the absorption of carbon dioxide by seawater — isn’t turning coastal waters into hydrochloric acid, but it can have a profound impact on marine life, local businesses and southern New England’s way of life.
Rhode Island, Massachusetts and Connecticut are among 15 states
whose shellfish industries are at long-term economic risk from the impact of
ocean acidification, according to the 2015 study funded
by the National Science Foundation.
Among the concerns, according to the study’s authors, is that many
of the most economically dependent regions, such as Massachusetts, New Jersey
and Louisiana, are least prepared to respond, with minimal research and
monitoring assets for ocean acidification.
While Northeast fisheries face lower acidification rates than the
Pacific Northwest, their vulnerability is higher, according to Lisa Suatoni, a
senior scientist for the Natural Resources Defense Council.
“Massachusetts and Maine are places that are just screaming for
problems,” Suatoni told Climate Central last year. “New Bedford is the highest
earning fishing port in the country. Eighty-five percent of landings are coming
from one species: scallops. They’re really vulnerable.”
Southern Massachusetts brings in more than $300 million in
shellfish annually, accounting for most of the region’s fisheries revenue,
according to Climate Central.
Rob Rheault, executive director of the East Coast Shellfish
Growers Association, told The Westerly Sun late
last year that he is waiting for more scientific evidence to show how an
increasingly acidic ocean will impact oysters and clams.
“Right now, the science on the impacts is weak,” he told the
newspaper. “The only thing that we know for sure is that the larvae, in that
first 48-hour period before they start feeding, are tremendously susceptible to
dissolution. Their energy budget goes negative because they haven’t started to
feed yet, and if they haven’t got enough energy in that egg and they’re
starting to dissolve, then it takes extra energy to lay down shell, and they
sometimes don’t make it.”
Of the 23 U.S. coastal regions identified by the Natural Resources Defense Council, 16 of them
will face ocean acidification levels unfavorable for shellfish. Overlaying
social factors, levels of agricultural runoff, local pollution and upwelling, a
natural ocean process that brings more corrosive deep ocean water to the
surface, helps tease out regional differences in vulnerability. (NRDC)
Acid hits
Oceans store dissolved carbon dioxide for hundreds of years,
creating a large-scale environmental problem that is causing wholesale changes
to ocean chemistry worldwide, according to a 2013 study.
Long Island Sound is just one example of acidification’s impact.
The tidal estuary between Connecticut and New York is feeling the effects
caused by excess carbon dioxide, according to the Connecticut
Fund for the Environment. The New Haven-based nonprofit has noted
that the sound’s low-oxygen dead zone forces finfish from local waters and
kills shellfish.
Low oxygen levels (hypoxia) begin with massive algal blooms,
caused largely by runoff that contains nitrogen and phosphorous. The blooms
then die and decay on the seafloor, sucking in dissolved oxygen. Research from the University of Stony
Brook suggests that bacteria feeding on the decaying algae also emit carbon
dioxide, which reacts with seawater to form carbonic acid. Researchers at the
New York university are examining the link between hypoxia and ocean
acidification.
This dual threat is a considerable concern for both Connecticut’s
environment and economy. The state’s shellfishing industry generates about $30
million annually and accounts for some 300 jobs, according to the state
Department of Agriculture.
More than 70,000 acres of shellfish farms are under
cultivation in Long Island Sound alone, and shellfish account for about 70
percent of all Connecticut fisheries’ revenue, according to the agency.
Since 1998, when Connecticut’s lobster catch hit a record 3.7
million pounds, the numbers have dropped significantly. In 2013, the Nutmeg
State lobster catch was 121,700 pounds, according to the Department of
Agriculture.
Varying explanations have been theorized — overfishing, warming
waters, pollution and habitat loss — but Connecticut isn’t alone when it comes
to changing saltwater chemistry and adjusting populations of marine life.
The world’s oceans haven’t been able keep pace with increasing
greenhouse-gas emissions. After decades of absorbing nearly a third of excess
atmospheric carbon dioxide, the planet’s salt waters are suffering from acid
reflux.
Shellfish help keep southern New England’s coastal waters and
wetlands healthy by filtering out pollutants. (R.I. Sea Grant)
Acid sinks
While the shellfish that inhabit the region’s coastal waters are a
popular part of southern New England’s social and cultural fabric, they also
are integral pieces of a marine ecosystem that provides economic and
recreational opportunities, and environmental benefits.
Southern New England has spent plenty of time and taxpayer money
upgrading stormwater systems and better managing runoff. Shellfish, most
notably oysters and mussels, are efficient at taking excess nitrogen, supplied
by wastewater treatment facilities, agricultural operations and over-fertilized
lawns, out of vital marine waters.
A 2004 study published in Science that involved analyzing 70,000
ocean samples taken worldwide in the 1990s found that 48 percent of carbon
dioxide produced by human activity between 1800 and 1994 — 467 billion tons —
had been absorbed by seawater.
The burning of fossil fuels since the Industrial Revolution has
made the oceans, on average, 30 percent more acidic at the surface, according
to the National Oceanic and Atmospheric Administration (NOAA). The world’s five
oceans also absorb about 90 percent of the heat trapped by increasing levels of
carbon dioxide and other greenhouse gases in the atmosphere.
NOAA scientists have projected that the world’s oceans and coastal
estuaries will become 150 percent more acidic by the end of the century.
Seawater is naturally alkaline, with a healthy pH that ranges from
7.8 to 8.5 (7 is neutral). But with a daily intake of some 22 million metric
tons of carbon dioxide, these waters are losing the ability to handle the acid.
This change in seawater chemistry, caused by an increased
concentration of hydrogen ions, also impacts the behavior of non-calcifying
organisms. For example, the ability of certain fish to detect predators is
decreased in more acidic waters, according to NOAA research.
When marine waters absorb carbon dioxide, carbonic acid — the same
acid that gives soda its fizz — is formed. This acid dissolves the shells of
mollusks, crustaceans and zooplankton, leaving the foundation of the marine
food web vulnerable.
More carbon dioxide in the oceans means slower growth, thinner and
more fragile shells, and poor shellfish reproduction, according to Newport,
R.I.-based Sailors for the Sea. When excess carbonic acid
is present, the formation of calcium carbonate becomes difficult and can
dissolve shells that have already been formed.
The corrosion of shellfish caused by increased carbon dioxide in
the water will reduce U.S. shellfish production 10 percent to 25 percent in the
next five decades, according to the Woods Hole Oceanographic Institute (WHOI).
“The current rapid rise in atmospheric carbon dioxide levels, due
to our intensive burning of fossil fuels for energy, is fundamentally changing
the chemistry of the sea,” Scott Doney, a WHOI senior scientist, wrote in
testimony he presented to the House Committee on Science and Technology during
a hearing in 2008 on the Federal Ocean Acidification Research and Monitoring
Act.
“Acidification threatens a wide-range of marine organisms, from microscopic
plankton and shellfish to massive coral reefs, as well as the food webs that
depend upon these shell-forming species.”
During the past 250 years, atmospheric carbon dioxide has
increased by nearly 40 percent, in large part because of fossil-fuel combustion
and deforestation, according to Doney. In that time, the world’s oceans have
absorbed some 525 billion tons of carbon dioxide.
Ocean acidification could also impact the millions of people that
depend on the oceans for food and jobs. Fish and marine organisms provide, on
average, 15 percent of the world’s protein. Americans alone spend about $60
billion annually on fish and shellfish. And reef losses would expose low-lying
areas and biologically diverse regions to storm surge and wave damage.
Employees of the Matunuck Oyster Bar farm at work on Potters Pond
in South Kingstown, R.I. (R.I. Sea Grant)
More study needed
Shelley Brown, education director for Sailors for the Sea,
testified last year at a House Committee on the Environment and Natural Resources
hearing for a bill that would create a Rhode Island marine acidification study
commission.
“Ocean acidification not only posses a serious threat to Rhode
Island marine species and ecosystems, but also our economy,” Brown said.
In Rhode Island, this change in ocean chemistry could threaten the
nearly 15,000 jobs in the state’s marine trades sector and $418 million in
annual taxes and fees, said Brown, who holds a doctoral degree that focuses on
microbial ecology in coastal marine environments from the University of Rhode
Island.
The bill’s sponsor, Rep. John Edwards, D-Tiverton, noted that
other states, such as Maine and Maryland, have set up similar study
commissions. In Maine, where lobsters account for 80 percent of fishery
revenue, there is considerable concern about the impact of acidification, he
said.
“Rhode Island has a vibrant fishing economy and we want to make
sure we keep that intact,” Edwards said.
URI oceanography professor Susanne Menden-Deuer testified at the
hearing that creating a commission to study the available science and identify
management strategies for Narragansett Bay is a good idea. She noted, however,
that “it wouldn’t suffice to isolate the effect of ocean acidification but
rather look at the multiple stressors that estuaries are subject to.”
She said it’s tricky to detect ocean acidification in estuaries,
because the effects of runoff often appear as acidification.
Ocean Conservancy scientist Sarah Cooley
said shellfish will experience the negative effects of ocean acidification
first. Rhode Island is highly vulnerable because of the heavy harvest of
oysters and quahogs, she said.
Cooley also said the Ocean State is vulnerable because
Narragansett Bay experiences the negative effects of excess nutrients and
runoff, which worsens ocean acidification. She said these challenges present
opportunities to create tailored responses to acidification.
The bill was held for
further study.
MIT is studying the impact ocean acidification is having on
phytoplankton and what that could mean for the entire marine food web and the
fishing industry. (R.I. Sea Grant)
Impact on food web
A team of researchers from MIT and the University of Alabama has
found that increased ocean acidification will dramatically affect global
populations of phytoplankton — microorganisms on the ocean surface that make up
the base of the marine food chain.
In a study published last July in the journal Nature Climate
Change, the researchers reported that increased ocean acidification by 2100
will spur a range of responses in phytoplankton: some species will die out and
others will flourish, changing the balance of plankton species worldwide.
The researchers also compared phytoplankton’s response not only to
ocean acidification, but also to other projected drivers of climate change,
such as warming temperatures. For instance, the team used a numerical model to
see how phytoplankton as a whole will migrate significantly, with most
populations shifting toward the poles as the planet warms. Based on global
simulations, however, they found the most dramatic effects stemmed from ocean
acidification.
Stephanie Dutkiewicz, a principal research scientist in MIT’s
Center for Global Change Science, noted that while scientists have suspected
ocean acidification might affect marine populations, the group’s results
suggest a much larger upheaval of phytoplankton — and therefore probably the
species that feed on them — than previously estimated.
“I was actually quite shocked by the results,” said Dutkiewicz,
the paper’s lead author. “The fact that there are so many different possible
changes, that different phytoplankton respond differently, means there might be
some quite traumatic changes in the communities over the course of the 21st
century.
A whole rearrangement of the communities means something to both the
food web further up, but also for things like cycling of carbon.”
Dutkiewicz also noted that shifting competition at the plankton
level may have major ramifications further up the food chain.
ecoRI News staffer Tim Faulkner contributed to this report.