Ocean acidification puts NW Dungeness crab at risk

May 18, 2016, NOAA Headquarters
Survival of Dungeness crab larvae, called zoeae, declined at the lower pH levels expected with ocean acidification. Credit: Jason Miller

Ocean acidification expected to accompany climate change may slow development and reduce survival of the larval stages of Dungeness crab, a key component of the Northwest marine ecosystem and the largest fishery by revenue on the West Coast, a new study has found.

The research by NOAA Fisheries' Northwest Fisheries Science Center in Seattle indicates that the declining pH anticipated in Puget Sound could jeopardize populations of Dungeness crab and put the fishery at risk. The study was recently published in the journal Marine Biology.

Ocean acidification occurs as the ocean absorbs carbon dioxide from the combustion of fossil fuels. Average ocean surface pH is expected to drop to about 7.8 off the West Coast by 2050, and could drop further during coastal upwelling periods.

Dungeness crab is the highest revenue fishery in Washington and Oregon, and the second most valuable in California, although the fishery was recently closed in some areas because of a harmful algal bloom. The Dungeness crab harvest in 2014 was worth more than $80 million in Washington, $48 million in Oregon and nearly $67 million in California

"I have great faith in the resiliency of nature, but I am concerned," said Jason Miller, lead author of the research, which was part of his dissertation. "Crab larvae in our research were three times more likely to die when exposed to a pH that can already be found in Puget Sound, our own back yard, today."

Survival of Dungeness crab larvae, called zoeae, declined at the lower pH levels expected with ocean acidification. Credit: Su Kim/Northwest Fisheries Science Center

Scientists collected eggs from Dungeness in Puget Sound and placed them in tanks at the NWFSC's Montlake Research Laboratory. The tanks held seawater with a range of pH levels reflecting current conditions as well as the lower pH occasionally encountered in Puget Sound when deep water wells up near the surface. Larvae also went into tanks with the even lower-pH conditions expected with .

"The question was whether the lower pH we can expect to see in Puget Sound interferes with development of the next generation of Dungeness crab," said Paul McElhany, a NOAA Fisheries research scientist and senior author of the paper. "Clearly the answer is yes. Now the question is, how does that play out in terms of affecting their life cycle and populations overall?"

Larvae hatched at the same rate regardless of pH, but those at lower pH took longer to hatch and progressed through their larval stages more slowly. Scientists suggested that the lower pH may reduce the metabolic rate of embryos. That could extend their vulnerable larval period, or could jeopardize the timing of their development in relation to key food sources, researchers suggested.

Larval survival also dropped by more than half at lower pH. At pH 8.0, roughly equivalent to seawater today, 58 percent of the - called zoeae - survived for 45 days. At pH 7.5, which sometimes occurs in Puget Sound now, survival was 14 percent. At pH 7.1, which is expected to roughly approximate the pH of water upwelling on the West Coast with ocean acidification, zoeae survival remained low at 21 percent.

"Areas of greatest vulnerability will likely be where deep waters, naturally low in pH, meet acidified surface waters," such as areas of coastal upwelling along the West Coast and in estuary environments such Hood Canal, the new study predicts.

Explore further: New West Coast mission investigates ocean acidification threat

More information: Jason J. Miller et al, Exposure to low pH reduces survival and delays development in early life stages of Dungeness crab (Cancer magister), Marine Biology (2016). DOI: 10.1007/s00227-016-2883-1

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aksdad
1 / 5 (1) May 18, 2016
Anyone who has ever owned a saltwater fish tank will tell you that it takes weeks to let the environment stabilize before you put fish or coral in it otherwise you'll end up killing a lot of expensive tropical fish (and coral). What do you think happens when you take Dungeness crab larvae and expose them to a pH level they are not accustomed to?

This kind of experiment tells us nothing about what's happening in Puget Sound or the oceans. It does tell us that Dungeness crab larvae are sensitive to sudden changes in pH. The predicted pH change due to CO2 absorption is far slower than that in the experiments, happening over numerous generations of, for example, Dungeness crabs, which allows them to adapt; something most organisms do over many generations. Remember Darwin's finches?

I grieve for the future of science if this level of reasoning is the status quo in current doctoral candidates.
leetennant
5 / 5 (1) May 18, 2016
"The question was whether the lower pH we can expect to see in Puget Sound interferes with development of the next generation of Dungeness crab..."

So, aksdad, you're saying the time taken to let the "environment stabilise" is intergenerational? Saltwater fish must be the worst pets ever.
leetennant
5 / 5 (1) May 18, 2016
What you're actually saying is that 'of course larvae die when exposed to these conditions, which is why they shouldn't be exposed to these conditions'. When the point is, they're *already* being exposed to these conditions because ocean acidification is happening that quickly.
aksdad
1 / 5 (1) May 18, 2016
Speaking of supposed pH changes due to CO2 absorption...

You can see what the measured pH trends are here from ocean buoys and hydrographic cruises:

http://www.pmel.n...map/text

Physics tells us that CO2 absorbed by seawater should lower the pH but so far observations show very little, if any, pH response to increasing CO2.

If you dig through the graphs you'll find 3 things of interest:

1. there are very few long-term observations so there's hardly any data
2. the seasonal fluctuations in pH are far larger than any long-term trend
3. the data don't match up with the reports of supposedly acidifying oceans

The hue and cry over ocean acidification is (surprise!) overblown. Studies show that observations of shellfish die-offs and coral bleaching are largely the result of natural processes, not CO2 absorption. See the conclusion in this paper:

http://myweb.facs...2010.pdf
aksdad
1 / 5 (1) May 18, 2016
the point is, they're *already* being exposed to these conditions because ocean acidification is happening that quickly

Look through the link to NOAA's PMEL graphs that I just posted and show us where ocean acidification is happening "that quickly".

It isn't.

Shellfish in some places in Puget Sound are being exposed to lower pH levels but not because of CO2 absorption from the atmosphere. Read the conclusion from the paper by Feely, et al. that I posted and see what it says are the predominant reasons for decreasing pH levels in Puget Sound, where they actually studied it and where Dungeness crabs live. Hint: it's not atmospheric CO2. It's natural.
leetennant
5 / 5 (1) May 18, 2016
You mean the paper that says

"We estimate that ocean acidification can account for 24 - 49% of the pH decrease in the deep waters of the Hood Canal sub-basin of Puget Sound relative to estimated pre-industrial values. The remaining change in pH... results from remineralization of organic matter due to natural or anthropogenically stimulated respiration processes within Puget Sound. Over time, however, the relative impact of ocean acidification could increase significantly, accounting for 49 - 82% of the pH decrease in subsurface waters for a doubling of atmospheric CO2."

So either you can't read or you are so biased you literally read the opposite of what a paper says. You've quoted that one before - you even put a similar quote in a comment before - and I was as gobsmacked then as now. It says the opposite of your contention.
Shootist
1 / 5 (1) May 19, 2016
Oceans have been more acidic that today and Crustaceans have been around for 500 million years. Nothing man can do with cause that to change.

If you don't support nuclear fission power plants your concern about carbon is political, misguided . . . and that's redundant.
Bongstar420
1 / 5 (2) May 22, 2016
I doubt these things are threatened. Its not like they are a newly evolved species or highly specialized. pH tends to fluctuate wildly on small scales as well anyways

Besides, we try to eradicate all kinds of things without success.

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