Metabolic response to stress in Olympia oysters (Guest Post)

Over the next few weeks students from the University of Washington FISH310 course (Biology of Shellfishes) will be providing insight into some of their independent research projects and thoughts on Olympia oysters in Puget Sound.

Today we have a post by Jessica Knoth

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Contrary to popular belief, the large Pacific oysters (Crassostrea gigas) found throughout the Salish Sea are not native to the area. Instead, the smaller and isolated populations of Olympic oysters (Ostrea lurida) are. They live in the intertidal zone along rocky shorelines, and in the 1800’s European settlers started harvesting them. This continued until the population eventually collapsed. Currently, there several remnant populations of Olympia oysters in the Puget Sound. Oyster Bay and Dabob Bay appear to have lower oyster survival and growth rates than the other two locations. For this reason, we decided to study both populations’ metabolic responses to stress.

Olympia oysters are sensitive to salinity, temperature, toxins, and other stressors. Ocean acidification, for example, has been detrimental to population growth (Hettinger et al. 2012). Larvae in the experiment were raised under different pHs. Those in a pH of 7.8 had a 15% decrease in larval shell growth rate, and a 7% decrease in shell area at settlement, when compared to the control larvae. After settling, the ‘stressed’ juveniles had a 41% decrease in shell growth rate (Hettinger et al. 2012). Temperatures above 40°C or below 0°C are also associated with significant mortality.

Judging by the growth and survival rates, Dabob Bay and Oyster Bay are not ideal places for Olympic oysters to live. However, small populations have continued to persist there. Because of this, we could safely assume that the oysters surviving there were fairly hardy. Dabob Bay has harsher conditions than Oyster Bay, so we hypothesized that the Dabob population will have a less drastic response to stress than the Oyster Bay population. To measure this, we induced stress on the oysters, took tissue samples, and then ran qPCR to measure the amount of glutamine synthase (a stress response gene) expressed in the two populations. We could measure the amount of glutamine synthase expressed by counting the amount of qPCR cycles it took for it to show up. A higher cycle number means it took longer for the synthase primer to react, which means there was a lower concentration of the stress response. Whichever oyster population had a higher number of cycles is the hardier population. For the experiment, we spun the two populations of oysters in a salad spinner to induce stress. We then took tissue samples and ran qPCR to determine the levels of glutamine synthase expressed. The more cycles it took for the glutamine synthase to show up, the less of it was expressed by the oyster. After normalizing with Actin, we found that Oyster Bay oysters expressed more glutamine synthase than Dabob oysters. This means they were more stressed by the salad spinner, which confirmed our hypothesis that Dabob Bay oysters are ‘tougher’ than Oyster Bay oysters – or at least they react less to acute stress. This is probably because they live in a stressful environment and are used to it. Hopefully, better understanding of stress inducement in Olympia oysters will lead to improved management and conservation of their populations.

I went into this project with next to no knowledge about oysters. For one, I thought Pacific oysters were native to the Puget Sound. I also found it interesting to learn how qPCR cycles worked. I’ve run PCR before for biology classes, but I’ve never used it in a real situation. I appreciate that our data may have real research applications.

References:

Hettinger, A., Sanford, E., Hill, T.M., Russell, A.D., Sato, K.N.S., Hoey, J., Forsch, M., Page, H.N., Gaylord, B. (2012). Persistent carry-over effects of planktonic exposure to ocean acidification in the Olympia oyster. Ecology 93:2758-2768.

Cheng, B.S., Bible, J.M., Chang, A.L., Ferner, M.C., Wasson, K., Zabin, C.J., Latta, M., Deck, A., Todgham, A.E., Grosholz, E.D. (2015). Testing local and global stressor impacts on a coastal foundation species using an ecologically realistic framework. Global Change Biology.