Ocean pH spells more trouble for oysters and oystermen

Many months ago, I posted on the topic of Vibrio tubiashii infesting local waters and jeopardizing the viability of Whiskey Creek Shellfish Hatchery in Netarts, OR.  Whiskey Creek supplies larvae for hundreds of West Coast oyster producers.  V. tubiashii is a little understood bacteria that thrives in deep waters, and seems to tolerate a lower pH. After nearly a year of work with Oregon State University and others, the hatchery installed ultraviolet lights and other sterilization procedures for its Netarts Bay intake water that successfully lowered the pathogen counts in their tanks.

Whiskey Creek Shellfish Hatchery, Netarts, Oregon. Photo by R. Emanuel

Whiskey Creek Shellfish Hatchery, Netarts, Oregon. Photo by R. Emanuel

When I visited the owners late this spring, a new situation had arisen: lowered pH in the water was also killing off or weakening the microscopic larvae. With lowered pH levels–and thus higher acidity, the young creatures cannot construct shells and successfully move into another stage as “seed” attached to a hard substrate (or surface).  After this second, serious setback, hatchery owner Sue Cudd was openly pessimistic about the future of the hatchery or the shellfish business, at least her’s in Oregon.

According to a June 14th article in the Seattle Times, Washington State shellfish growers seem to be experiencing similar problems related to ocean water pH.  The evidence points to increased carbon dioxide levels in sea water off the entire Pacific Northwest Coast.

As Craig Welch reports:

Now, as the oyster industry heads into the fifth summer of its most unnerving crisis in decades, scientists are pondering a disturbing theory. They suspect water that rises from deep in the Pacific Ocean — icy seawater that surges into Willapa Bay and gets pumped into seaside hatcheries — may be corrosive enough to kill baby oysters.

If true, that could mean shifts in ocean chemistry associated with carbon-dioxide emissions from fossil fuels may be impairing sea life faster and more dramatically than expected.

Recent work by researchers such as Zeebe et al. 2008 and Orr et al. 2005 indicate that atmospheric CO2 emissions are driving carbonic acid levels in sea water to historic highs (in human, not geologic terms). Carbonic acid is produced when gasseous carbon dioxide is dissolved in water. Though only midlly corrosive, carbonic acid reduces the most common and accessable dissolved form of calcium carbonate: aragonite.  Aragonite is the basic building block of shellfish shells.  The lack of aragonite, in turn, reduces the ability for shellfish to grow and produce new layers of calcium carbonate shell. In larvae, which in most organisms start out shelless, the acidic environment and lack of aragonite prevents any shell production, dooming the young to a short existence or a weakened state where they may be more vulnerable to predators.

At present, we’re at the stage of seeing anecdotal evidence that backs up modeling and lab-based research.  This is an important trend, however–one that we should keep our eyes on as it develops in the next few years.

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