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Going Green: Beyond shells

Researchers delve into impacts of ocean acidification on key finfish species

Herring is a commercially important species, as it’s used for lobster bait.  - Photo courtesy of Gulf of Maine Research Institute
By Lisa Duchene
March 05, 2012

We know seawater is becoming more acidic, as the oceans absorb some of the rising carbon dioxide emissions spewed into the atmosphere. We also know that spells big trouble for marine life, evidenced by shellfish die-offs in the Pacific Northwest.

But what’s just starting to emerge is exactly what ocean acidification (OA) means for finfish stocks like cod and forage fish like herring. The first study on a commercially important fish, Atlantic cod, came out in December and is among the first in a handful of studies in the last few years in which scientists have done laboratory and controlled ocean experiments, exposing finfish species to rising CO2 levels and noting the physiological effects.

A team of scientists led by Andrea Frommel at the Leibniz-Institute of Marine Sciences in Kiel, Germany, exposed Atlantic cod larvae to three levels of CO2 — present-day, projections for the end of the next century and an even higher level possible under extreme coastal upwelling conditions — over two-plus months in a controlled, ocean experiment. (The institute changed its name to GEOMAR-Helmholtz Centre for Ocean Research Kiel on Jan. 1.)
Frommel’s team found CO2 exposure at those levels resulted in severe to lethal tissue damage in many internal organs of Atlantic cod and that the degree of damage increased with CO2 concentrations.

“As larval survival is the bottleneck to recruitment, ocean acidification has the potential to act as an additional source of natural mortality, affecting populations of already exploited fish stocks,” wrote Frommel and co-authors in a paper published online Dec. 11, 2011, in the journal Nature Climate Change.

“This paper shows evidence that climate change has the potential to really affect recruitment of larval fish to the spawning population and this needs to be taken into account in fisheries models and in setting future quotas,” wrote Frommel in an email. “So far, this factor has been completely neglected.”
No studies have yet examined the effect of rising CO2 levels in seawater on fish populations, nor have any directly linked CO2 levels to the current or future health of fish stocks.

To understand the state of the science on the effects of more acidic seawater due to rising levels of carbon dioxide, it helps to think about a jigsaw puzzle. The handful of published studies represents the first few pieces of a 1,000-piece puzzle.

Investigative efforts into CO2 impacts on finfish are in their infancy, says Chris Chambers, research fishery biologist at the National Marine Fisheries Service Northeast Fisheries Science Center in Sandy Hook, N.J. “One cannot draw generalizations of the effect of CO2 and finfish,” he says, because these first few studies looked at different species in different environments, measured different responses and used different methods of implementation. 

Those larger studies — the critical puzzle pieces that flesh out patterns, define the bigger picture and begin to answer questions about the effects on populations — are likely two to three years off, says Chambers. So it will be awhile before buyers can know the implications of ocean acidification on supply and sourcing.

Chambers is researching several species as part of the National Oceanic and Atmospheric Administration’s ocean acidification program that began in August 2010 and that also involves work out of the Northwest Fisheries Science Center in Seattle. Chambers and his colleagues strategically selected fish species to represent various life history types and habitats. They are looking at Atlantic tomcod (a relative of Atlantic cod), fluke, winter flounder, black sea bass and two sturgeon species.

Andrea Franke and C. Clemmesen, also scientists at GEOMAR in Germany, studied elevated concentrations of CO2 in Atlantic herring. They found no effects on a number of physiological effects like hatch rate, length, dry weight, yolk sac area and otolith (earbone) area of newly hatched larvae.
But they did find an indication that rising CO2 levels can negatively affect the metabolism of herring embryos. They found lower RNA concentration, which can lead to decreased protein biosynthesis, according to their study, published Dec. 15, 2011 in Biogeosciences.

“This can have consequences for the larval fish, since smaller and slow-growing individuals have a lower survival potential due to lower feeding success and increased predation mortality,” according to the study.

Overall that study indicated good news for Atlantic herring, says Jeffrey Runge, professor of oceanography at the University of Maine School of Marine Sciences based at the Gulf of Maine Research Institute in Portland. Herring is an ecologically important forage fish in the Gulf of Maine that is also commercially harvested as bait for Maine’s lobster industry.

“It’s way too early to make any conclusions,” says Runge, “but we’re not yet finding any dramatic effects on herring.”

Of concern for Gulf of Maine herring, says Runge, is the combination of lower pH and warming of Gulf of Maine surface waters. Ocean acidification, of course, does not occur in a vacuum and is occurring as water temperatures warm. There may well be a combination effect upon the lipid-rich zooplankton that herring feed on. 

Observation systems in the Gulf of Maine and elsewhere would help researchers observe and track what is happening, but we are falling short of that goal, says Runge.

The takeaway for buyers?

“I think they need to pay attention to what’s happening in the ecosystem,” says Runge. “We’re not going to be able to predict it very well, but it would be in their best interest to watch what’s happening over time.” 

Contributing Editor Lisa Duchene lives in Bellefonte, Pa.

March 2012 - SeaFood Business 

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