Graduate students whose research is centered at FHL go off to postdocs and jobs in various segments of society. We don’t keep statistics, but in my experience the majority head for academic jobs, others into federal and state agencies, non-profits, and consulting companies. Grace’s essay shows that she has a clear goal of working in natural resource management — a world where not only science is important but an understanding of policy, and excellent public communication. Grace has managed to build all those skill sets during her graduate career, many right here on San Juan Island, and we look forward to seeing where she goes next!

Best,
Dr. Megan Dethier, FHL Director
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Environmental Tradeoffs From an Oyster’s Eye View

My first summers at UW’s Friday Harbor Labs were all about learning adaptive mussel trade-offs.  As a National Science Foundation REU (undergraduate) intern and then a technician for two summers, I studied how mussel beds could spell their own demise even as they provide habitat for hundreds of organisms.  While working for Emily Carrington and Mike Nishizaki, we collected data on the low dissolved oxygen conditions inside of mussel beds.  These circumstances create a doom loop where low flow and increased respiration drive down oxygen concentrations to lethal levels.  Yet, being in a bed could also help mussels thrive: the surface roughness of mussel beds alters water flow in a way that can bring more juvenile mussel larvae to the bed, and ensure that more mussels become adults.  Beds can also provide shade and water retention that keeps mussels cool when exposed to air.  Those same benefits impact other species that live inside of mussel beds, such as limpets and barnacles.

Once a graduate student at UW, I began to wonder how the structure of the mussel bed might further influence the depletion of oxygen or the cooling of the organisms.  A multi-layer bed might lead to more oxygen depletion (hypoxia) because of the high density of animals, but would mussels be less metabolically active underwater if they didn’t need to breathe as hard (i.e. the cooling benefits of the bed kept them from needing to respire as much)?  Was there a point at which the tradeoffs could be optimized for the ecology of the organism, where mussels could keep their cool without suffocating?  Moreover, could the answers gleaned from mussel beds be applied to other situations?

Enter the Pacific Oyster: a species from across the Pacific Ocean that was brought to the US to earn its keep as a commercial aquaculture species.  Emily had just received funding from Washington Sea Grant to work with climate resilience of oysters grown in Washington shellfish farms, and I wanted to use my future PhD to build a career working in natural resource management.  Oysters are often grown in intertidal aggregations – theoretically creating similar conditions to mussel beds – and are a species that could connect me to the resource management community.  All I needed was a place to do the work, and FHL provided the resources I needed to answer my questions: expert staff and faculty, housing, a wind tunnel, a seawater-compatible flume, and the nearby oyster farm of Westcott Bay Shellfish.

I first tested how oyster aquaculture modifies heat transfer inside an oyster bed, and if it mimics the cooling that mussels experience.  Oyster aquaculture provides a unique system to study this question because oysters are stocked at varying densities depending on the farm, creating structural variability and multi-layer beds.  Thus, applying the logic of mussel beds, I hypothesized that high stocking densities may produce differences in body temperature between oysters positioned on the top of a bed (more solar heat input but good convective water cooling) relative to the bottom of a bed (shaded from solar heat but only limited convective cooling).  This disparity could potentially lead to variability in growth and survival within the same stock.  Understanding what layering scheme/density is optimal for oyster temperatures and having a cost-effective method for tracking those body temperatures (like biomimetic “Robo” temperature loggers) may help growers identify thermal risk in their stock and adjust their practices to a warming climate.

So, I spent the summer of 2024 with Emily Carrington’s custom wind tunnel in Lab 6, heating up different densities of oysters under a range of wind speeds and comparing live oyster temperatures to biomimetic robo-oyster temperatures to see if robo-oysters could accurately track live oyster temperatures (Figure 2A).  Oyster temperature declined with wind speed as the air increased convective cooling.  However, the fun result was that under hot lights and low wind speeds, oysters on the bottom of a dense group were 10°C cooler than the ones on top in aquaculture bags that were half full (2.5 oyster layers), but hardly any cooler when at lower layer densities (Figure 2B).  Higher densities kept the oysters on the bottom insulated at the expense of the top ones taking the brunt of the heat.

I next wanted to evaluate the other side of that tradeoff, testing how many layers a bed could have before oysters depleted the oxygen inside an aquaculture bag.  Moreover, could increased water flow “rescue” oysters from total hypoxia by increasing mixing within the bed, much like in my lab mate Kindall Murie’s work (Murie, 2025) with mussels?  Kindall wrote a Tide Bite in January 2025 and is now a postdoc at Stanford’s Hopkins Marine lab with another FHL alumnus, Brooke Weigel.

I conducted two experiments in Lab 6’s “big flume” to test this idea and build a model of hypoxia risk in cultured oysters.  Much like the wind tunnel experiment – but in water – I tested different densities under different flow speeds, this time putting oxygen loggers in the water and in the oyster bed (Figure 3A).  Again, half a bag (an oyster bed with 2.5 layers) appeared to be the tipping point, reducing oxygen by up to 1 mg/L: a catastrophic decline if a farm’s oysters are already experiencing near hypoxic conditions (Figure 3B).  However, flow speeds above 1 or 2 cm/s (similar flow speeds found in a sheltered bay) can “rescue” oysters and keep oxygen levels relatively normal.

This experiment presented the other side to the tradeoff: oysters may be protected from extreme heat (stocking at higher densities) or low oxygen (stocking at lower densities), but they can only dodge one problem. However, my work also presented solutions: keeping densities to around half a bag full could mitigate the worst of either problem. Furthermore, for maximizing yield, farmers could get creative: shade your oysters with recycled shells to limit heat exposure, while placing them in an area of higher tidal exchange on the farm to limit oxygen depletion and keep growth moving at a steady pace. Westcott Bay Shellfish has started to spread oysters on their beach outside of bags, keeping density low while their vertical posture in the mud can prevent intense solar heating.

Half a bag seemed to be the effective density limit to gain benefits, but how did the oysters perform in the field when faced with either side of the density tradeoff? How would this tradeoff affect oyster yields for farmers? I put oyster bags with densities higher and lower than the half-a-bag tipping point in the field at Westcott Bay Shellfish, this time with a twist: I placed them at different tidal heights to expose them to either a) more air exposure (and more heating) in the high intertidal or b) more submersion in the low intertidal (greater risk for oxygen depletion). I’m still processing the results, but while the lower density groups in the high intertidal saw higher temperatures, and the dense groups in the low intertidal saw lower oxygen, the oysters were resilient to both. Growth and survival changed with tidal height, but not density.

The tradeoff turned out to not be driving survival in the field. However, that means oyster growers can likely stock oysters at higher densities without seeing negative effects, clearing the way for this species to still be workhorses and drive a key sustainable industry in Washington.

The oysters faced tradeoffs, but I did not face any working with them. I got to build my own lovely working relationship with the Westcott Bay farm and restaurant staff, co-creating science with the Westcott Bay farm managers. My midday field work on the farm allowed me to talk with Westcott’s restaurant patrons about FHL, the importance of funding science, and the sustainability of oyster farming. I got to collaborate with undergraduate students, high school students, and other labs like Kendall Valentine’s in UW Oceanography. My experiences seeing how state institutions like Friday Harbor Labs can assist the broader community through sustainable aquaculture earned me a science communication fellowship in Washington D.C. through the Ecological Society of America. I got to advocate for federal funding for science in congressional offices with other ecologically trained graduate students. That internship also gave me a valuable opportunity to evaluate whether I want to pursue working in the government after school (I still do), and connected me with people who could help get me there.

The only thing I haven’t done in my six summers at FHL is face a tradeoff about the Labs itself: it’s all upside. I’ve been nurtured by a tight-knit community of elite researchers and staff in world-class facilities, all while not having to financially stretch to come up here thanks to the generous support of FHL’s student research fellowship programs. Ecology may present tradeoffs but students at FHL don’t have to, so they can continue to develop and become great scholars and stewards of the natural world.

Grace’s work was funded by the Friday Harbor Laboratories Research Fellowship Endowment, the Charles Lambert Memorial Endowment, Friday Harbor Beatrice Crosby Booth Endowed Scholarship, the UW Biology W.T. Edmondson Award, the UW Biology Friday Harbor Labs award, National Science Foundation Award No. 2050273 (Awarded to E. Carrington, M. Reidenbach & M. Nishizaki), the National Science Foundation’s Graduate Research Fellowship, the REU-Blinks NSF REU Fellowship, and Washington Sea Grant (UW, NOAA-NA24OARX417C0026-T1-01. The views expressed herein are those of the author(s) and do not necessarily reflect the views of NOAA or any of its sub-agencies).

Reference:

Murie K.  2025.  Flow as a mediator of ecosystem engineering: Hydrodynamics shape chemical modification by kelp and mussel beds.  Dissertations & theses @ University of Washington.

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