Any significant differences among the remnant populations? (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 Karl Seitz

The Project

In the Pacific Northwest, the native Olympia oyster (Ostrea lurida) has been subjected to a number of stressors such as, overharvesting, competition with introduced commercial species, and habitat degradation, which have resulted in much reduced population levels (White et al., 2009). Special reserves were set up and strict harvesting guidelines were established but, the populations have not recovered well on their own (White et al., 2009). Due to this lack of natural recovery many state, tribal, commercial, and nonprofit groups have begun to show interest in active restoration of the species (White et al., 2009). For proper restoration to occur it must first be determined if there are any significant differences among the remnant populations and if so which population(s) should be used in the reintroductions?

Here we attempted to answer whether or not there are significant differences between different populations of Olympia oysters in Puget Sound, WA. We examined individuals from two areas of Puget Sound, Dabob Bay in the northern section of Hood Canal and Oyster Bay in southern Puget Sound just west of Olympia, WA. In order to determine if the populations differed we exposed them both to a mechanical stress (salad spinner) and looked for differences in their response to that stress. We measured their rates of oxygen consumption as a proxy for metabolic rate and also performed qPCR on gill tissue samples to compare expression of heat shock proteins (HSPs). From previous studies of these and other populations (Heare, unpublished data) we suspected Dabob to be a heartier stock and hypothesized that those individuals would exhibit a higher metabolic rate and expression of HSPs after stress than the Oyster Bay individuals.

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Results

We saw that, after normalization using actin expression, the expression of HSP was higher in the Oyster Bay individuals which was opposite of what we hypothesized. This may be because the Dabob population is more accustomed to stress events and therefore has a lower expression due to acclimatization to a stressful environment. The Oyster Bay individuals, being from a less stressful environment, may overreact to stress events since they are not accustomed to dealing with harsh conditions.

We also saw that prior to stress the Dabob population had a higher rate of oxygen consumption but, that after stress showed markedly lower consumption than the Oyster Bay. This was also opposite of our original hypothesis but, may be attributed to the type of stress we subjected them to and that Dabob may be accustomed to stress events. Since we subjected them to mechanical stress it seems logical that the oysters would close up to protect their internal structures from damage and in the closed condition oysters will not be consuming much oxygen. If the Dabob population is accustomed to repeated stress events it may explain why their oxygen consumption rates dropped and stayed low because they may stay in the closed condition awaiting further stress. Oyster Bay on the other hand closed for a shorter period of time before re-opening and increasing their metabolism to recover from any damage incurred by the stress.

Though our hypotheses were wrong we did observe differences in the populations’ response to stress. Our preliminary results suggest that the populations may possess distinct phenotypic differences that may be important considerations when planning restoration activities. Further statistical analysis of our data will prove whether these differences are in fact significant and prompt further investigation into these and other populations.

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References

White, J.M., E.R. Buhle, J.L. Ruesink, and A.C. Trimble. 2009. Evaluation of Olympia oyster (Ostrea lurida Carpenter 1864) status and restoration techniques in Puget Sound, Washington, United States. Journal of Shellfish Research 28:107-112.

Stay tuned tomorrow as Karl tells us what he thinks can be improved!