Ocean acidification a culprit in commercial shellfish hatcheries' failures

December 16, 2014 by Cheryl Dybas
Mediterranean mussels at the Penn Cove Shellfish Farm in Washington's Puget Sound. Credit: Penn Cove Shellfish Farm

The mortality of larval Pacific oysters in Northwest hatcheries has been linked to ocean acidification. Yet the rate of increase in carbon dioxide in the atmosphere and the decrease of pH in near-shore waters have been questioned as being severe enough to cause the die-offs.

Now, a new study of Pacific oyster and Mediterranean mussel larvae found that the earliest larval stages are sensitive to saturation state, rather than (CO2) or pH (acidity) per se.

Saturation state is a measure of how corrosive seawater is to the calcium carbonate shells made by bivalve larvae, and how easy it is for larvae to produce their shells. A lower saturation rate is associated with more corrosive seawater.

Increasing CO2 lowers saturation state, the researchers say, and saturation state is very sensitive to CO2.

The scientists used unique chemical manipulations of seawater to identify the sensitivity of saturation state for larval bivalves such as mussels and oysters.

Results of the study, which was funded by the National Science Foundation (NSF), are reported this week in the journal Nature Climate Change.

"Biological oceanographers have speculated that early life stages of marine organisms might be particularly sensitive to , but the underlying mechanisms remain unknown for most species," says David Garrison, program director in NSF's Division of Ocean Sciences, which funded the research through an ocean acidification competition.

NSF's Directorates for Geosciences and for Biological Sciences supported the ocean acidification awards.

"This research is an important step," says Garrison, "in being able to predict, and perhaps mitigate, the effects of ocean acidification on coastal resources."

Commercial hatchery failures

The findings help explain commercial hatchery failures, and why improving water chemistry in those hatcheries has been successful.

Shellfish hatcheries are now altering water chemistry to create more favorable saturation state conditions for young bivalves.

View of the Penn Cove Shellfish Farm, where mussel larvae are sensitive to ocean acidification. Credit: Penn Cove Shellfish Farm

"Bivalves have been around for a long time and have survived different geologic periods of high carbon dioxide levels in marine environments," says George Waldbusser, an Oregon State University (OSU) marine ecologist and biogeochemist and lead author of the paper.

"The difference is that in the past, alkalinity (the opposite of acidity) levels buffered increases in CO2, which kept the saturation state higher relative to pH. In the present ocean, the processes that contribute buffering to the ocean cannot keep pace with the rate of CO2 increase.

"As long as the saturation state is high, the oysters and mussels we tested could tolerate CO2 concentrations almost 10 times what they are today."

The idea that bivalve development and growth is not as linked to CO2 or pH levels as previously thought initially seems positive.

However, the reverse is true, Waldbusser says.

Marine ecologists study ocean water chemistry back in the lab. Credit: Oregon State University

Larvae sensitive to saturation state

Larval oysters and mussels are so sensitive to the saturation state (which is lowered by increasing CO2) that the threshold for danger will be crossed "decades to centuries," says Waldbusser, ahead of when CO2 increases (and pH decreases) alone would pose a threat to bivalve larvae.

"At the current rate of change, there is not much more room for the waters off the Oregon coast, for example, to absorb more CO2 without crossing the threshold," Waldbusser says.

The study builds on previous research by Waldbusser and colleagues that outlined the mechanisms by which young bivalves create their shells after fertilization.

The researchers found that young oysters and mussels build their shells within 48 hours to successfully begin feeding at a rate fast enough to survive, and that the rate of shell-building required significant energy expenditures.

Scientists have found that shellfish are affected by what's called saturation state. Credit: Wikimedia Commons

In the presence of acidic water, the oysters and mussels had to divert too much energy to shell-building and lacked the energy to swim and get food.

Sinking shellfish

"The hatcheries call it 'lazy larvae syndrome' because these tiny oysters just sink in the water and stop swimming," Waldbusser says.

"These organisms have really sensitive windows to ocean acidification—even more sensitive than we thought."

In the current study, the researchers used high-resolution images to analyze the development of oyster and mussel shells.

The effects of low saturation state waters were tested on oyster larvae. Credit: Oregon State University

They found that the organisms—which are about 1/100th the diameter of a human hair—build a complete calcium carbonate shell within six hours, about 12 hours after fertilization.

Alter the ocean chemistry just a bit, however, and a greater proportion of the shells do not develop normally.

Two-day-old Pacific oyster larvae showed abnormal growth with changes in saturation state. Credit: Oregon State University

The ones that do are smaller, leading to potentially weaker organisms that take longer to get to a size where they can settle into adult life.

"When the water is more saturated and has greater alkalinity it helps offset higher levels of carbon dioxide, ensuring that shell formation can proceed—and also making the shells bigger," Waldbusser says. "This can have a significant effect on their survivability."

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9 comments

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gkam
4.5 / 5 (8) Dec 16, 2014
Do we still have Deniers?
Modernmystic
5 / 5 (7) Dec 16, 2014
Do we still have Deniers?


I'm wondering just what it is they're denying anymore and why.

We have empirical evidence of;

A warming trend (both in the oceans and air)
Rising CO2 levels
CO2 traps IR heat

Does it even MATTER if it's caused by humans or not at this point? That's a rhetorical question...NO it doesn't matter. The fact is that levels are rising and we're not helping that trend. In the interest of a more stable environment (no such thing as the "correct" environment) and billions of people not being displaced we need to stop with the coal, oil, and gas. It's just so not worth even debating anymore or fretting over who's to blame.
tadchem
1 / 5 (4) Dec 16, 2014
The statement "Increasing CO2 lowers saturation state" would seem to contravene Le Chatelier's Principle:
CO2(gas) + H2O (liq) >> CO2(soln)

Modernmystic
5 / 5 (3) Dec 16, 2014
pH increases the solubility of CO2 in water...
mbee1
1.4 / 5 (10) Dec 16, 2014
This article is about junk science. The PH of the oceans areas involved has not changed at all. the oysters may have a problem but that problem is not universal so the most likely reason is disease of some kind. The ascertain that the we have a warming trend currently is simply untrue. The IPCC claims a slowing but the actual data shows no warming for at least 16 years, no trend in the mid and lower troposphere in 55 years, CO2 is a very poor greenhouse gas and helps cool the planet in the upper atmosphere, the ice core studies of co2 and climate change show co2 never caused a climate change in the past 800,000 years. The models used to project future warming do not work and have never worked. they are not tested on any period before 1951 and cannot predict he current hiatus or the hiatus from 1940 to 1980, the cooling from 1880 to 1912 much less the medieval warm period or the little ice age. You can believe what you will but the science simply does not support AGW.
gkam
4.2 / 5 (9) Dec 16, 2014
mbee, where do you get your "real" science?
Modernmystic
5 / 5 (5) Dec 16, 2014
[q}CO2 is a very poor greenhouse gas{/q}

Well you guys are big on "natural" cycles....during the PETM CO2 levels reached about 2000 PPM...no other atmospheric gas was significantly different than it was today. This 500% rise in CO2 is the only significant difference between now and then accounting for a 12 degree F change in temperature.

Those are the facts. Give another PLAUSIBLE correlation and I'm all ears....
Real_Scientist
1 / 5 (1) Dec 16, 2014
@Modernmystic if you read the research article, this will answer your question. Alkalinity in the ocean was much higher during the PETM, thus offsetting the acidifying effect of the higher CO2. When CO2 comes from volcanoes, weather of the continents increases, due to the plate movements, which delivers more alkalinity to the oceans...

Do you guys usually post with such fervor without actually reading the science the stories are based on?
aksdad
1 / 5 (2) Dec 22, 2014
As with virtually every experiment showing detrimental effects of ocean acidification or seawater saturation state, the organisms are subjected to a rapid change in their marine environment which has no corollary in nature. Any seawater aquarium owner knows sudden changes in the seawater stress the organisms in the tank and can even kill them. In the ocean, these changes typically take place over hundreds or thousands of years and are so gradual that it is likely the organisms will adapt especially over the span of hundreds of generations. Current measurements of pH at various sites show a very gradual trend. See, for example:

http://www.epa.go...ity.html

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