It’s no secret that ocean acidification threatens many forms of wildlife, but a recent study suggests some species may actually possess built-in defenses against increasing acidity.
Researchers at Oregon State University have found that Olympia oysters—native to the west coast of Canada and the United States—are fairly resilient to the effects of ocean acidification.
Canadian Geographic spoke to lead researcher Dr. George Waldbusser to learn more about these fascinating oysters.
How do Olympia oysters differ from the Pacific oyster, which you’ve studied in the past?
Pacific oysters release eggs and sperm into the water and then fertilization occurs. The Olympia oyster, on the other hand, is interesting because it broods the larvae, meaning the female actually pulls the sperm in from the water and fertilization occurs internally. We were really trying to understand how ocean acidification impacts these early life history stages. So the first thing we had to do was figure out how to grow larvae outside of this brood chamber. If not, it would be difficult to tell if our manipulation of the water chemistry was actually having a direct effect on the larvae. As it turns out, we were able to extract the fertilized eggs from the female and they developed normally. The fact that brooding appeared to have no direct physiological benefit was really interesting and probably could have been published on its own!
What effect did changing the water chemistry have on these Olympia oyster larvae?
Changing the chemistry of the water was our way of simulating ocean acidification. The first time we ran the experiment across an incredible range of chemistry conditions, and we found absolutely no response—in very poor and corrosive waters the Olympia larvae developed just fine outside of the brood chamber. Initially we thought maybe we had made a mistake. So we repeated the experiment, this time with both Pacific oyster larvae and Olympia oyster larvae. The end result was the same—there seemed to be no effect of higher acidity levels on the Olympia oysters, whereas the Pacific oysters were less resilient to these changes.
What could explain this result?
Oysters and mussels develop a shell through calcification, a process that typically takes about six hours and by the end of that time, about 80 to 90 per cent of their body weight is shell. But what we found with the Olympia oysters is that their calcification rate is much slower than this and occurs later on (a couple of days after fertilization). We also found the Olympia oysters consumed a lot less energy lipids during this time than the Pacific oysters. So basically Olympia oysters don’t experience the same acute sensitivity in their early life stages that many other bivalve species experience, and this appears to be related to the rate at which they make their shell and their energy status during this time (i.e. this slower calcification rate requires much less energy).
Does this research tell us anything about the effects ocean acidification may have on Olympia oysters in the long term?
Not exactly. It’s challenging to keep the larvae in the laboratory, so we haven’t looked at long term effects. The critical thing here is we’ve been able to identify a lack of sensitivity to ocean acidification in the oyster’s early life stage, and I suspect that while they are more resilient to this phenomenon, they aren’t completely resistant to it in the long term.
What is the current conservation status of Olympia oysters?
As with most edible oysters, they have been excessively over-harvested. Prior to the west coast gold rush, they were a dominant feature in many estuaries. Since then, there have been many attempts to restore their populations. They seem to slowly be recovering, but they’re not anywhere close to what their historical populations were.
Why is this type of study important?
We have a rather bleak view for a lot of marine calcifiers about what ocean acidification will do to them in the future, so studies like this are important to fill these knowledge gaps. A study like this also helps us take a step back and recognize that animals possess a wide variety of traits that help them adapt to changing conditions. In this particular instance, slow shell building probably didn’t initially evolve as a way for oysters to adapt to increased water acidity; rather it likely evolved to cope with a whole suite of other ecological challenges. But it does give us hope that nature has some tricks up her sleeve to deal with changing environmental conditions.
This interview has been edited for length and clarity.