In simple terms, ocean acidification refers to the pH level of the seas decreasing -- and when we talk about it now, we're talking about it happening too quickly. Tessa Hill, a University of California, Davis professor in the Department of Earth & Planetary Sciences, works out of the school's Bodega Marine Laboratory in Sonoma County. She has partnered with Hog Island Oyster Co., one of the stars of the Bay Area food scene, to study how this ocean acidification effects sea life, especially oysters. Those little critters are, in addition to delicacies, very important filters. When they go, so goes the ocean, is the thinking. We talked with Hill and Hog Island Oyster Co. partner Terry Sawyer about their work.
Can you explain, in layman's terms, what ocean acidification is, and why it's bad?
Tessa Hill: Ocean acidification is the long term change in seawater chemistry due to the absorption of carbon dioxide from the atmosphere. Human-caused emissions of carbon dioxide fundamentally change the chemistry of seawater. Animals living in seawater are accustomed to a range of chemical conditions, and those conditions are changing, rapidly, due to human impacts.
Terry Sawyer: OA is a broad term that describes the effects associated with the burning of fossil fuels, the subsequent release of CO2 into the atmosphere, and
the changes in ocean chemistry as the CO2 is absorbed by the global ocean. It is a problem, with obvious (measurable) changes in pH, that when combined with further changes (increasing temperatures, hypoxia, and other parameters -- at a rapid rate), are having significant negative effects on larval and juvenile species that build their shells from minerals in the sea water. This directly impacts the species that I grow for food.
What role do oysters play in keeping the ocean healthy?
Hill: Oysters are filter-feeding invertebrates -- they eat material that is floating in the water -- which helps maintain the estuarine environment. They are also "engineers" in an ecosystem, because the oysters (and their shells) provide habitat for other animals to live on or around.
Sawyer: Oysters are filter feeders that feed on phytoplankton that occurs in estuaries. If they were not present, the water clarity would be significantly reduced, and marine plants would not be able to survive at any real depth, thus marine nursery systems would be reduced, affecting the entire ecology. The presence of a food species require high water quality that is constantly monitored by shellfish farmers, and is a built-in mechanism to know what is happening in ecosystems that are changing due
to manmade environmental pressures.
Why is the thinning of oyster shells such bad news?
Hill: Our research group at Bodega Marine Laboratory raises animals in the lab under "future" conditions, which in this case includes more acidic water. In the laboratory, we see that under future, more acidified conditions, oyster shells tend to be smaller. Those smaller shells are more susceptible to predators, and possibly other stressors, like disease.
We have also raised mussels in the laboratory. Mussels only get a little bit smaller under future, more acidic conditions, but they also get measurably thinner. This means they are likely more susceptible to predators or drying out in the hot sun during a low tide.
In both cases, the animals are weakened by the process of acidification, compared to oysters and mussels that are not exposed to acidified conditions.
Sawyer: The ability of the farmed species to build shells directly parallels the ability of many organisms to build shells - and we can see the changes in
many life stages because we are operating in the same marine environment.
How did the partnership with Hog Island Oysters and University of California come to pass?
Hill: Terry approached us -- we had met at a meeting of scientists, managers, and aquaculture industry members. This was over three years ago now. He had an idea that we could work together to investigate the impact of ocean acidification on Tomales Bay and on aquaculture species. It has been a tremendously successful partnership, from my perspective. We have learned so much about the vulnerability of Tomales Bay to acidification, and our research group finds the partnership with Hog Island Oyster Co. very rewarding.
Sawyer: I was attending conferences addressing the increasing signs that changes in ocean chemistry, alongside research scientists and other stakeholders,
and realized that I could help address some of the physical challenges of monitoring parameters by just being in the marine environment every day, as well as be able to understand the issues as we all learned. The monitoring allows me to not only develop management practices to try to adapt, but through the sharing of this data, we all could possibly work together to raise the issue and possibly help to develop strategies to slow the rate of change, much less help to show that it is real and having real effects. Collaboration helps to get results!
What are the goals of the partnership?
Hill: We are interested in understanding the natural variability of the Tomales Bay ecosystem in terms of acidification -- for example, are there times of the year that would be more vulnerable to this process than others? Also, providing information that is of value to the sustainable aquaculture community for planning and adaptation to the threat of ocean acidification and using this partnership as a vehicle to talk to the public about how ocean acidification impacts our daily lives: the food on our plates, family businesses, sustainable food, and our local environment.
One of the most exciting aspects of this partnership is that all of the data we collect in Tomales Bay are publicly accessible, in real time. Anyone interested in this issue can access the same data we have, and we hear from scientists and managers that the data are being used for a variety of purposes.
Our work on ocean acidification is a big, collaborative effort at Bodega Marine Laboratory. I am part of a team of four faculty, plus graduate students, researchers, and staff, that all work on this together. This is a big problem that requires many people investigating it from different points of view.
Sawyer: I believe we (society) have a tendency to put things in a box and think that it is nice and tidy ... simplistic. As we have been discovering more and more, the ecosystem changes are extremely complex, far reaching, and we need to have a better understanding of the issues in order to come up with a more complete strategy to address changes, that I believe, are absolutely necessary. These challenges will involve paradigm shifts in behaviors, in some cases.