by Margaret Conley, PhD student in Ocean, Earth, and Atmospheric Sciences
I study estuaries, the beautiful, mucky, and sometimes smelly mixing zones where river and ocean meet. Estuaries are exciting because they are always changing. Of course, every place has its seasons. Here in Oregon, we have summer sun and winter rain, spring flowers and fall leaves. But in an estuary, these changes are amplified: On top of seasonal changes, there is the daily drama of the tide, alternately flooding and exposing mud flats and marshes. The tide and the seasons also bring changes we can’t directly see — how warm and salty the water is, for example. These invisible characteristics are critical for the creatures that make estuaries their home, including oysters.
Oysters are used to a certain degree of change. But how will they, and their estuarine home, respond to the larger changes that human-caused climate change will bring? This is what my fellow researchers and I are trying to figure out, and we’re starting by better understanding the dynamics of one of the most basic water characteristics: temperature. We are studying water temperature in the Yaquina Bay estuary in Newport, OR to figure out how it changes with tides, storms, and seasons. Once we better understand the current range of temperature changes, we can start to predict how the estuary might change in the future, and how all this change affects the plants and animals that live in the estuary.
We are measuring the temperature of estuary water at many locations, from far upriver where the water is fresh to the salty water at the estuary mouth. By looking all along the channel, we can witness the battle between ocean and river, pushing each other back and forth as the strength of the tides and the river flow change over time. We’re also measuring the mucky places, like tidal flats where the water comes and goes and side channels called sloughs. All these water sources, plus heat from the sun, combine to determine the temperature of the water in the estuary. By recording the temperature changes from tide to tide and season to season, we hope to identify which factors are most important in determining temperature at each location along the estuary. We also want to figure out how these conditions influence where oysters grow best.
Besides the changing waters, the assortment of plants and animals that live in the Yaquina Bay estuary also changes over time. Baby salmon travel through estuaries on their way to the sea, and birds use the Yaquina as a rest stop during migration or as a summer or winter vacation home. Just like me, these animals are temporary visitors, and they never see the full range of estuary conditions. But there are also those who make this changing place their permanent home. Just like the residents of waterside towns, organisms like oysters set up shop on a particular spot and stay put. To understand why oysters live where they do, we have to become permanent residents too.
That’s where the scientific instruments come in. These little machines let us become residents of the estuary. While we return home to Corvallis after each field trip, the instruments stay behind, quietly recording the changing waters. While we work in our offices, they brave winter storms, floating logs, encroaching mud, and curious creatures. With luck, plus lots of knots and tape, they are still there when we return, and they report back on what they’ve seen. Each time we visit, the instruments look like they’ve been claimed by the estuary, coated in brown goop to match the muddy bank, sprinkled with baby barnacles just like the nearby rocks. Crabs move into our bottom moorings as they slowly sink into the muck. If we didn’t return soon enough, they might just disappear entirely.
Using these measurements, we plan to figure out what the oysters themselves already know: How does the temperature of the water change over time? After several months of measurements, we can already start to put together a story. We see the winter rainstorms that push ocean water down the estuary back towards the sea, changes in the coastal ocean that creep their way up the estuary with the tides, and solar-powered heating. Once we know how temperature in the estuary changes, we can try to predict how it will be impacted by climate change. This temperature change also contributes one piece of the puzzle in understanding how oysters, intrepid inhabitants of this changing place, will respond.