Study: Blue crab larvae harmed by low oxygen, high acidity

Blue crab larvae died at greater rates in waters with higher acidity and lower oxygen levels — conditions likely to intensify with climate change and increased nitrogen, according to a new study by Stony Brook University researchers.

While the impacts of low oxygen on marine life have been studied, the research is the first to assess the consequences of these two stressors on larval crabs, the authors said. High acidity, or low pH, and low oxygen, known as hypoxia, are worst in summer, when blue crabs are breeding, according to the peer-reviewed paper published in the online journal PLOS One.

The effects could offset a predicted boon for Long Island’s blue crab population caused by warming waters, authors said. 

The Stony Brook study used egg-carrying female crabs collected in Shinnecock Bay and shipped from the University of Maryland, Baltimore County, and subjected the larvae to pH and oxygen levels that could be found in back bays.

"We wanted to simulate real-world conditions in degraded estuaries," said lead author Stephen Tomasetti, a doctoral student at the university's School of Marine and Atmospheric Sciences.

The tasty crustaceans, also known as blue claw crabs, are found up and down the East Coast, including in the Island's bays and harbors. From 2010 through 2016, commercial fishermen in the United States had an annual catch worth at least $175 million, according to federal statistics cited in the paper.

The research was conducted in the lab of Christopher Gobler, a professor in the school. He and students Brooke Morrell and Lucas Merlo were co-authors.

During 14 days in moderately low oxygen and acidic conditions, each condition individually reduced survival of the larvae by 60 percent and 49 percent, respectively. Combined, the stressors reduced the survivability level by 87 percent when compared with a control group. During four-day experiments, low pH had no effect on survivability of larvae, while low oxygen did affect survivability. 

Other research has predicted that climate change actually could help blue crab populations on Long Island, which is near the northern limit for the species.

The Department of Environmental Conservation, in a 2016 report on recreational crab fishing, said warming waters will result in "increased winter survival, productivity, and northward range expansions of their populations."

In 2017, New York commercial fishermen landed nearly 200,000 pounds of the crab, up from 109,000 pounds landed in 2013 and down from a recent peak of 282,000 pounds in 2016, according to the state DEC.

Gobler agreed that climate change could be good news for blue crabs in New York, but said the Stony Brook study highlights that the local estuaries will have to have good water quality.

Many studies of marine life have only taken into account low oxygen levels, he said, but scientists now know that low oxygen and high acidity are found together.

“One of the big take-aways is that acidification matters and needs to be considered when it comes to managing fisheries,” he said. 

Gobler has previously published studies on the negative effects of high acidity and low oxygen on clams, scallops, oysters, mussels and small schooling fish.

The study of blue crab larvae shows the need to control local pollution in bays and waters — especially with global action to address climate change appearing unlikely, Gobler said.

"We should double down on controlling regional sources of nitrogen-loading to improve water quality conditions," he said.

Officials have blamed homes not connected to sewers, fertilizers and the atmosphere for rising nitrogen in the water, which can cause algal blooms harmful to shellfish.

John Tanacredi, executive director of Molloy College's Center for Environmental Research and Coastal Oceans Monitoring, cautioned against over-extrapolating the results of the blue crab study. He was not involved in the Stony Brook research.

The health of local waters has been “vibrant, dramatically improved,” he said, based on almost two decades of monitoring the Great South Bay's waters, with abundant populations of the plankton-eating menhaden, bluefish and striped bass. Tests by the center show the water has gotten more acidic, but oxygen levels have been steady.

"Dissolved oxygen levels have been robust," Tanacredi said. "Those waters are as rich as you can make them."

Earlier this year, Gobler said that Stony Brook water tests found 30 sites with low oxygen and low pH around Long Island.