Ocean acidification could mean bad news for Dungeness crab

As local fishermen continue to ply their trade in Del Norte County waters, scientists are studying the effects of climate change on a myriad of species including Dungeness crab.

In an action plan published October 2018, the State of California outlines priorities for research into ocean acidification caused by global carbon dioxide emissions by the burning of fossil fuels, including prevention and adaptation.

According to Jessica Williams, project scientist for the Ocean Science Trust, which has been working with the California Ocean Protection Council, though the research into the impacts of ocean acidification is new, there will be a lot of impacts to several different species. This includes Dungeness crab as well as the algal blooms that contribute to fisheries closures due to domoic acid, Williams said.

“Scientists are still trying to figure out what those impacts will be,” she said. The Ocean Science Trust released an infographic recently focusing on the impacts of ocean acidification. “This infographic (is) demonstrating what we currently know about the direct impacts and there’s active research, not only for direct impact on species and what that means, but indirect impacts we might not see.”

One scientist, Paul McElhany, at NOAA’s Northwest Fisheries Science Center in Seattle, has been part of an experiment trying to understand the sensitivity of Dungeness crab to the high carbon dioxide levels that contribute to ocean acidification.

He said he and his colleagues focus on the larval stage, rearing crab under controlled carbon dioxide conditions that simulate the current environment as well as a projected future environment with higher carbon dioxide conditions.

“What we’ve seen so far is under high CO2 conditions, larvae have a lower survival and slower development rate,” McElhany said.

So far, it’s been a challenge to extrapolate what that might mean for the overall Dungeness crab population, according to McElhany. He and his fellow researchers are also running a number of other experiments expanding on those initial results, including trying to determine how crab do under multiple stressors such as changes in temperature and changes in oxygen concentrations. They’ve also studied how crab at later developmental stages respond to higher carbon dioxide concentrations, McElhany said.

Crab typically mate in the spring, McElhany said. The female then extrudes her eggs, deposits them onto her abdomen in the fall, nestles down in sediment over the winter and the eggs hatch in the spring. Hatchlings, called zoea, don’t look at all like a crab, McElhany said, and live in the water column. The transition from this stage to maturity can take two or more years, he said.

“In the first set of experiments, we took females that had eggs already attached to them into the lab,” McElhany said. “When those eggs hatched, we reared (them) in the zoea stage in water with controlled CO2 conditions, current CO2 levels and future CO2 levels. What we saw in those experiments is the zoea under higher CO2 conditions, they had lower survival (rates). Not as many lived as compared to current day CO2 and they also developed slower.”

At later juvenile stages, McElhany said it appears that crab are more resilient to higher CO2 conditions than they are at the zoea stage, though those results haven’t been published yet. However, he noted that slower development can cause them to delay reaching necessary milestones as the season progresses.

“They need to get to a certain stage before winter sets in,” McElhany said. “The slower they grow, the longer they’re vulnerable to other predators. The quicker they get big, the harder it is for other things to eat them. We haven’t shown those impacts, but that’s a concern with slower developmental rate.”

According to McElhany, the amount of carbon dioxide in the water can vary. Concentrations in the Puget Sound area on average are higher than on the Washington coast. He said it has largely to do with ocean circulation patterns and the input of fresh water, noting that freshwater has a lower pH than sea water.

However, McElhany said, because of the upwelling pattern in the Pacific Ocean, there are some areas on the West Coast with high concentrations of carbon dioxide. That water also tends to be lower in oxygen, but higher in nutrients, he said.

Ocean acidification can have a potential impact on the Dungeness crab fishery, especially because of its potential effects on domoic acid. Though the commercial season in Crescent City normally starts on Dec. 1, unsafe levels of the toxic algae delayed the season until Jan. 25.

Jessica Cejnar, Del Norte Triplicate, 18 February 2019. Article.

Ocean acidification could mean bad news for Dungeness crab