My field season started with a midnight arrival into LA on Monday, June 23 followed by a 10 hour drive to Medford, OR the next day. These back to back traveling days were good preparation, as they became more the norm than the exception over the next few weeks. I arrived into Willapa Bay, WA the afternoon of Wednesday, June 25 and met up with Jennifer Ruesink and Alan Trimble from University of Washington, my hosts and guides for the next few days. They’ve been working in Willapa Bay for almost 20 years, and are fountains of information on the natural history, ecology, and local recruitment patterns of both the Pacific and Olympia oysters.
Before continuing, it’s worth mentioning why my sample collection schedule is structured the way it is, with a stretch of very busy days and then “down” time in between. While low tides usually remain at least a couple feet above the sea level mark (referenced as zero for describing tidal heights), there are certain periods that have a minus low tide where the tide falls below the zero mark. This is due to the sun and moon either being on exact opposite sides of the earth or on the same side. For the west coast of North America, the best minus tides are during the summer. Here are the estimated tides for Willapa Bay. Note how the minus tides start early in the morning and then gradually become later in the day.
Jennifer and Alan had two other people staying and working with them this tidal cycle: Alex Lowe, also a first year PhD student studying at UWash; and an intern, a recent high school graduate starting at UWash in the fall who was from a third-generation oyster farm. Jennifer is an excellent cook, and dinner that first night more than compensated for the fast food I’d been dining on the past few days. The conversation thoroughly tested my abilities to convey my knowledge of population genetics (most of which I had just learned a few months prior!) and what I intended to learn from these oyster species that wasn’t already known.
As proof that the best ideas come out of lively discussion, an additional potential project emerged from the chat. For as long as they’ve been working in Willapa Bay, Alan said that there was always an early set in July and a late set in August for the Pacific oysters. Set here refers to when the oyster larvae leave the water column and settle on their preferred substrate (usually other oyster shells), where they then stay for the rest of their lives. While there are always fewer larvae in the water before the early set, the proportion that survive to be juveniles is much higher than those in the late set. This may be because the early set are able to reach a bigger size before winter storms come and are better able to weather the rough conditions. From a genetics perspective, this poses a few interesting questions. Are the early spawning oysters more related to each other than you’d expect by chance? Is there a heritable trait that the early spawning adults have that confer them this advantage? What genes are responsible for this apparent shift in phenology that’s occurred for only some oysters in the population?