Kachemak Bay researchers look for trends

Studies aim to discover if ocean acidification is affecting species in Kachemak Bay, Cook Inlet

Enormous quantities of carbon dioxide present in Earth’s atmosphere are altering the chemistry of its seas, say scientists who warn that unless the trend is reversed, there is trouble ahead for ocean ecosystems, many of which support the world’s supply of seafood.

As studies continue worldwide, including in the deeper waters off coastal Alaska, researchers at the National Oceanographic and Atmospheric Administration’s Kasitsna Bay Laboratory have been probing the depths of Kachemak Bay and Cook Inlet in an effort to determine what, if any, effect ocean acidification is having on local species.

Much of that work is devoted to establishing a firm baseline of existing conditions against which future research results can be measured.

Kris Holderied is director of the Kasitsna Bay Laboratory, a facility owned by the NOAA’s National Centers for Coastal Ocean Sciences.

It is also home to University of Alaska Fairbanks’ cold-water scientific diving program. Holderied and other researchers are attempting to gauge the effects of tides and currents in and out of the bay, the impact of fresh water streaming off surrounding glaciers — the pace of which is increasing — and a host of other dynamic contributors to the bay’s chemical condition.

One way of gauging that condition is by measuring the water’s pH level — that is, determining how acidic or alkaline it is, Holderied said.

Temperature, pressure and salinity also are key measures, but pH is a prime concern.

The pH scale ranges from 0 to 14. Pure water is rated at 7, or neutral pH. A pH less than 7 is acidic. A pH greater than 7 is alkaline, also called basic.

Research shows ocean pH is falling and has been since the beginning of the Industrial Revolution when human industrial and agricultural activities began adding significantly to the natural quantity of carbon dioxide in the atmosphere through the increased use of carbon-based fuels, such as wood, coal, oil and gas, and from the clearing of huge swaths of carbon dioxide-eating forests.

Fortunately for the atmosphere — and us — the world’s oceans have buffered the impact by absorbing an estimated 25 percent of that carbon dioxide (according to researchers, more than 525 billion tons since the advent of the Industrial Revolution), thus slowing the accumulation of the greenhouse gas in the atmosphere.

But increasing the carbon dioxide in the water means a growing presence of carbonic acid, dropping pH still further toward the acidic.

Research compiled by the European Project on Ocean Acidification shows the slightly alkaline average surface pH of the world’s oceans has fallen from 8.2 to about 8.1 in the past 250-300 years

That doesn’t sound like much until you understand that the pH scale is logarithmic and that a 0.1 decrease equals a 26 percent change toward acidity. The pace of carbon dioxide production has increased dramatically in the past 50 years, and with it the rate of ocean acidification, research shows. If that trend goes unchecked, by century’s end acidity will have increased by 150 percent, directly threatening the existing biodiversity of the oceans.

Why is that important for Alaskans?

It turns out a more acidic ocean could impact species important to the state’s multi-billion dollar commercial and subsistence fishing economies.

Here’s an example of how: Increased acidity makes it hard for shell-making organisms that make up vital parts of ocean food chains to make and maintain shells. It’s an issue of energy: the more energy needed to make shells may mean less for finding food, avoiding being food, and reproduction. One of the main sources of food for some salmon species is the pteropod, a planktonic mollusk that depends on the availability of calcium carbonate, a compound negatively affected by increasing acidity. Less calcium carbonate means fewer pteropods. Fewer pteropods could mean fewer, or at least less weighty, salmon, a direct impact on Alaska’s economy.

The Arctic serves as a canary in the coal mine for ocean acidification, because many of its negative effects are first detected in cold, northern waters. Model projections reported by The Interacademy Panel on International Issues (IAP) indicate that Arctic waters will become corrosive “to arctic calcifiers such as pteropods, and bivalves such as clams, which play a key role in arctic food webs.”

Studies of acidification in Alaska coastal waters are being conducted by chemical oceanographer Dr. Jeremy Mathis, director of the newly established Ocean Acidification Research Center at the University of Alaska Fairbanks, who has been looking at deep ocean patterns off Alaska’s coastline. During recent roundtable discussions on acidification held in Homer, Dillingham and Kodiak sponsored by the Alaska Marine Conservation Council, Mathis told audiences, “We are past the tipping point for carbon dioxide in our oceans.”

In one study released in 2009, Mathis noted that pteropods make up half the diet of juvenile pink salmon and that a 10-percent decrease in the population of pteropods could result in a 20-percent decrease in the size of adult salmon. Pteropod decline raises several questions: how well could pinks alter their diet? Would switching prey put them in direct competition with other important species? What are the ripple effects to Alaska’s fishing industry?

Data from Mathis’ studies should help give Kachemak Bay researchers a sense of what’s coming, Holderied said, but at this time, scientists don’t yet know if trends seen elsewhere are present here. While sensors at Homer and Seldovia harbors provide relative measures of how pH, temperature and salinity change seasonally, they are too imprecise to supply the kind of details critical to a deeper understanding. Nevertheless, Holderied said, several cyclical drivers are known to lower pH in the bay over time — cold water naturally upwelling from the deep ocean, fresh water draining off glaciers and phytoplankton blooms. A new seasonal station at Bear Cove should help, she said.

Raphaelle Descoteaux, a graduate student at UAF, is currently looking at the impact of increasing acidification on larval crab in the bay. She tests how crab larvae react to decreasing pH levels by raising them in three different pH environments including at pH 8.1, the current seasonal average for the bay, at an intermediate level of pH 7.8, and at 7.5, which she said represents the bay’s probable pH within 100 to 200 years if nothing is done to curb atmospheric carbon dioxide. Viewed under a microscope, Descoteaux said some of the spines and appendages larvae use for protection against predators and, it is believed, for buoyancy were noticeably smaller.

“By making them shorter with acidification, it is possible we impair these functions, making them more susceptible to predators and to sinking,” she said.

Too little is known about conditions in the bay to make predictions beyond crab, but if they’re suffering ill effects, so might their predators, and on up the food chain to local fisheries.

“Everything is interconnected in the ocean,” Descoteaux said.

Similar inquiries are ongoing worldwide.

Recognizing ocean acidification’s potential for calamitous economic impact, President Barack Obama’s administration created the Interagency Ocean Policy Task Force, which, in 2010, recommended more monitoring, stating that ocean acidification was “expected to have significant and largely negative impacts on the marine food web, ocean ecosystems as a whole and biological diversity in general.”

Clearly, studying ocean acidification is more than a mere academic exercise, Holderied noted. But there’s a bigger issue: What’s to be done about carbon dioxide emissions? Ocean researchers suggest we might mitigate the effects of ocean acidification by cutting worldwide emissions to half of 1990 levels by mid-century. However, according to many of those same scientists, even if humans ceased pumping carbon dioxide into the atmosphere today, it would be decades if not longer before the downward trend of pH could be halted.

Meanwhile, the research effort in Kachemak Bay continues, funded by NOAA, the Alaska Ocean Observing System, as well as the Exxon Valdez Oil Spill Trustee Council.

Hal Spence is a freelance writer who lives in Homer.

Hal Spence, Homer Alaska – News, 25 July 2012. Article.

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