Researchers Study Survival Odds for Alaska's Lucrative Crab Fisheries
July 1, 2017
Dynamic conditions and predators in the waters of the North Pacific Ocean notwithstanding, Alaska's lucrative commercial shellfish industry faces growing challenges from ocean acidification and climate change.
It's a concern felt by all those engaged in the harvest of Alaska's wild shellfish, from commercial fishermen, for whom it is a multi-million dollar industry, to those taking crab for personal use and subsistence.
Can crab survive the increasing impact of global warming and increased ocean acidification?
"The wild stocks are going to be much more resilient than we understand," said Bob Foy, director of the Kodiak laboratory, as he stood by crab tanks, holding a female red king crab to expose her clutch of some 200,000 embryos.
"I really believe that. We have found a lot of negative impacts in the lab work, but given time they will be more resilient.
"Are they going to be resilient enough to keep our commercial fisheries at the level they are at? I don't know, but I think they will not just disappear."
At the 15-year-old seawater laboratory facility, the goal is to look at biological responses to how the crab react to changes in environment and each other in very controlled settings. "But that is not enough," Foy said. "We have to take those data and understand what it means in the real world."
Foy and his Kodiak lab team are engaged in extensive research to learn more about the survival potential of crab, from the embryonic stage through growth to adult size, in the face of increased stresses.
"We look at how well a mom can raise those embryos. So after a male and a female mate, she will hold those embryos for a year, all 200,000 of them, under her abdomen. She will aerate them, but that means wherever she is living they are living, and her condition when she mated affects their condition."
If the female king crab is stressed because of environmental conditions, the embryos may be compromised from day one, so now instead of 200,000 hatching, maybe only 100,000 hatch. Mortality when they are released is still the same, so maybe even fewer will survive seven years from when they were released.
The Kodiak team is part of an extensive network of research in other parts of the United States and beyond trying to determine the impact of ocean acidification and climate change on the ability of crab to build shells and other necessities of survival in the face of dynamic ocean conditions.
"If we want to maintain the crab stocks and support coastal communities, I think we should be looking toward mariculture," he said. "There are already some stocks that have not come back, like red king crab in the Gulf of Alaska, and blue king crab in the Pribilofs, where those stocks have not come back regardless of acidification. I think aquaculture is a possible tool to revive those stocks and provide some opportunity for local communities."
crab is, in fact, one of the species under consideration by the mariculture task force established by Alaska Gov. Bill Walker. "There is a lot of promise and some concern as well," Foy said. "You have to know how those crab are going to interact with animals in the wild. We are still working on what that feasibility is, whose crab are they, how you maintain those crab and the economic feasibility of such a program," he said.
Meanwhile, in tanks at the Kodiak lab, fisheries biologists are measuring the response of crab to water temperatures, levels of acidity and more.
"If just the larva stage is exposed to acidification, they can usually withstand it, but if the mom had already been experiencing increased stress because of acidification at the embryo stage, then they don't do well at the larva stage," Foy said.
"In general what you have to consider is how many of those embryos will make it, and very few of them make it," Foy said. "They have as many offspring as they can and let them loose and good luck. A lot can happen. The larva may be swept away by the current. They go through metamorphoses. They don't even look like a crab when they start, and a month later they start to look like a crab when they go through abrupt stages. About 30 days later they settle in the bottom of the ocean. If they settle in the wrong spot, they're dead," he said. Threats range from settling in water that is too hot or too cold to encountering predators.
Once the crab settle on the bottom of the ocean, they are in their juvenile stage and have to grow to a particular size so that the fishery can take them, so it is essential that they have the habitat needed to persist.
Ocean bottom temperatures vary a lot. "As the environment changes, as it is in the bering sea, that's going to affect this life stage," Foy said. "Often you don't know which way it's going to affect them."
"As the ocean warms, maybe there is more or less food in the water for them to live on. Maybe the currents change, because as temperatures change, as sea ice changes, the currents in the ocean change.
"We know there are warming trends. We know there is variability in the amount of sea ice. We know that the carbon dioxide levels are increasing. So all of those changes are going to affect whether or not the crab survive the different stages," Foy said. The North Pacific Ocean itself is a sentinel region for signs of ocean acidification.
Dissolving of carbon dioxide into the oceans increases the hydrogen ion concentration in the ocean, which in turn reduces ocean pH, making that water more acidic.
Corrosive waters also reach shallower depths more in the North Pacific, especially in Alaska, than in other areas of the oceans, so biological impacts of that acidification are likely to occur earlier than in many other places, NOAA notes. Meanwhile ocean acidification reduces the calcium carbonate saturation point, which may stress calcifying organisms by making calcification more difficult, NOAA said.
Researchers at the Kodiak lab started looking at ocean acidification roughly in 2006 and 2007, Foy said.
They started with some very basic experiments, changing pH, and then created more complex experiments, and got better at manipulating conditions in the lab where the crab were exposed to carbon dioxide. They started to measure a number of variables to see which crab survived and thrived. From there they looked at the amount of calcium carbonate in the shell, because the amount of calcium in the shell is sensitive to acidification.
From there they looked at how blood cells change as they are exposed to corrosive waters, and at genetics, at whether different genes are turned on or off when exposed to acidification, and at shell structure to see if the shell would break easier and if it became more brittle.
"We wanted to understand those mechanisms," he said.
The goal was to see what to expect in the next 10 generations of crab, and what environmental conditions they would be experiencing. They saw decreased survival, Foy said.
In a low pH environment researchers know the crab have to expend more energy on maintaining a constant pH in their blood, and these changes can affect the shell. While they didn't see a lot of changes in the shell, they found that the claws of king crab may be less hard.
"Claws are how they feed, and if they're more brittle, they can't crack open a bivalve," Foy said.
The Kodiak lab results left researchers anticipating that acidification at levels they expect to see over the next 50 to 80 years would increase the psychological stress to crab to a point of high mortality.
Working with their colleagues at the University of Washington on data each had compiled they found that in general once the bering sea reaches a pH of 7.5 that crab stocks would see recruitment failure within 20 years.
Still there was a great big caveat, in that the data is based on laboratory studies where crab were exposed immediately and they looked at the response within a year or two.
In reality, Foy said, "the bering sea is going to acidify at a slower rate. It's going to take years."
Now that the researchers understand how bad it could get, the goal now is determine the likelihood of the crab to acclimate.
"As it happens over the course of the next 50 to 80 years, each generation has an opportunity to react to this increase in pH, this change in carbonate, and they may adapt," Foy said. "We want to let fishermen know the vulnerability of their resources. Now our goal is to scale it, to determine whether or not these animals can acclimate. Maybe it's not as bad as we think it is."
The latest lab experiments are measuring how crab may react if exposed to carbon dioxide at different scales, what happens when carbon dioxide goes up and down every 12 hours, and then slowly increases over time.
The research is also looking at what happens to the crab who survive the pH experiments and to conduct new experiments on them, to see if they can adapt in the face of ocean acidification.
While much of the acidification in the ocean is manmade, natural processes also contribute to the buildup of carbon dioxide in these waters.
Every animal in the ocean respires carbon dioxide, so the oceans are absorbing carbon dioxide from all animals in the ocean. In the Atlantic Ocean, where the ocean conveyer belt starts, water sinks from the surface to travel along the bottom of the world's oceans, and as years go by they have accumulated a lot of carbon dioxide and become corrosive naturally. Then some of that water comes up in the North Pacific.
"In the North Atlantic, if you go down 3,000 meters you can still form shell because there is lots of calcium carbonate in the water," Foy said. "In the North Pacific, 100 meters down, you are already seeing corrosive water, so it is difficult for an animal that lives below that layer to build a shell."
"With all these natural processes there is CO2 in the water anyway," Foy said. "The colder the water, the more carbon dioxide it can hold, so it's a double whammy," he said. Offshore of the Pacific Northwest states of Washington and Oregon, an upwelling – when winds blow offshore and push surface waters off – the bottom water comes up, bringing with it all that naturally corrosive water.
"Shellfish hatcheries there are showing more of upwelling now than they did years ago. Chemical oceanographers are measuring that change," Foy said, but one thing they already know for sure is there will be increased acidification throughout our lifetime.