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Posted February 5, 2018
Maria Kavanaugh, newly appointed CEOAS assistant research professor, reviews a series of dynamic seascapes, pointing out impressionistic swirling eddies of color. But these works of art are rendered not on canvas but on a computer screen: They are mapped mosaics of regions in the ocean that have unique physical and biological characteristics, analogous to terrestrial landscapes, identified and characterized using satellite data.
“Landscapes are patches of unique habitats arranged in an orderly, hierarchical way on the planet, shaped mostly by geology and climate. The ocean is actually shaped similarly,” Kavanaugh explains. “The ocean contains smaller-scale features like eddies embedded in gyres, which are embedded in ocean basins. Instead of geology and climate, in the ocean it’s hydrology like currents and climate that control the mosaic.”
Using satellite data on phytoplankton (as represented by ocean color), sea surface temperature and other parameters, Kavanaugh and her colleagues identify distinct ocean regions so they can ask a range of questions: how do these regions shift and change size with changes in climate conditions? Is one area changing more rapidly than the regions around it? Does a region in the Pacific Ocean have an analogous region in the Atlantic? Is a particular piece of the patchwork mosaic more resilient to change than others?
“It can be difficult to ask these kinds of questions in the ocean because the ocean is always moving. We can’t repeatedly drop a bucket in the water somewhere and expect to sample the same parcel of water again,” Kavanaugh says. “It’s more of a challenge than studying a grove of trees that you can return to periodically.”
That’s why satellites are useful, as they can take images of vast areas of ocean simultaneously. Kavanaugh’s particular interest is the phytoplankton at the bottom of the food web. Satellite imagery can differentiate among large functional groups of phytoplankton, which is enough information to determine whether a “good” food source is available for upper levels of the food web. “It’s like being able to differentiate between a tree and a bush on the OSU campus—we couldn’t tell if we have, say, oak trees specifically. With respect to phytoplankton, we can differentiate groups of different cell sizes, which often tells us about the quality of that species as a food source,” Kavanaugh says. With information about the lower levels of the food web, scientists can make inferences about upper levels.
Other satellites examine sea surface temperature, salinity and sea surface elevation, which allows for calculation of ocean currents. Information from these satellite sources is integrated into large-scale seascapes of entire ocean regions or basins. Because all of these parameters change over time on a range of time scales, some of the most challenging and interesting questions Kavanaugh asks are related to temporal changes in seascapes.
Kavanaugh didn’t always take this big picture view. Her very first ecological study, undertaken as an undergraduate at the University of Oregon in a field course in quantitative ecology, zoomed in on algae in the intertidal zone at Cape Arago on the Oregon coast. “I was getting doused by waves, counting algae species on the rocks between each wave, but I had the best time,” Kavanaugh recalls. Having spent much of her childhood in a tiny town in eastern Oregon far from the ocean, this field course was the first time that she considered marine science as a career. “The idea that you could be out in the environment learning and working – that was amazing to me,” she says. “Up to that point I thought that to study the ocean you had to be Jacques Cousteau, scuba-diving in a tropical environment from a big boat.”
She continued her education, coming to Oregon State to research rocky intertidal ecology with Bruce Menge, Jane Lubchenco and PISCO (Partnership for Interdisciplinary Study of Coastal Oceans), where she was enthralled with the patterns and drivers of the vast diversity of species along Pacific rocky shores. However, she wanted a bigger-picture view, one that would afford a perspective of the ocean’s patterns and the large-scale processes that control them. She shifted to biological oceanography for her Ph.D. work, where CEOAS oceanography faculty member Ricardo Letelier guided her toward satellite imaging. When combined with her existing background in ecology, the study of pelagic seascape ecology was a natural next step.
Her doctoral work was a proof-of-concept project: she determined that satellite phytoplankton data could, indeed, be used as the basis to describe seascape mosaics. “We could identify patches containing different phytoplankton communities and biogeochemical functioning, and we could see those patches expand and contract on seasonal scales as well as interannually in the North Pacific,” she explains.
As a post-doctoral researcher at the Woods Hole Oceanographic Institution, she used the approach to characterize seascapes in U.S. coastal waters, participating in an ongoing inter-agency effort called the Marine Biodiversity Observing Network. “We are asking, what is the minimum number of things we need to measure to characterize marine biodiversity in a given region,” she says. “Seascape divisions allow us to determine whether we have sampled enough, and how one region may differ from another.” This work is being carried out in the Gulf of Mexico and coastal California, in partnership with the Florida Keys National Marine Sanctuary (NMS), the Monterey Bay NMS, and the Santa Barbara Channel Long Term Ecological Research Study.
Now back at Oregon State as a research faculty member, Kavanaugh will be using newly awarded NASA funding to expand the seascapes approach to two areas: the Arctic, and then (drumroll, please) the global ocean. The Arctic project will present a particular challenge, as cloud cover allows satellite imagery for only about six months of the year. In the Arctic, she will partner with a number of existing monitoring programs to answer questions about marine species-habitat relationships and how they could change with a warming Arctic.
As this method and framework evolves, Kavanaugh expects that it will be able to be used to answer a range of questions with management implications, especially when used in conjunction with data that other partners are collecting. For example, in 2014 and 2015, satellite data revealed low productivity water close to the Oregon coast associated with a warm water phenomenon that came to be known as “the blob.” The invasion of this water resulted in an abnormally small, compressed and shallow area of higher phytoplankton productivity, which matched NOAA data on where schools of anchovy were aggregated. Whales following the small fish into the shallow nearshore are at increased risk of entanglement with gear fixed to the bottom, such as Dungeness crab pots.
With the new NASA-funded project underway, the seascape paradigm will have been tested in a broad range of marine regions, from polar to subtropical. Kavanaugh is excited to determine how helpful this approach can be in characterizing the dynamic global ocean. “Marine species and pelagic habitats are not constrained by geopolitical boundaries. If we can examine how seascapes have changed and evolved over time, how pieces of the mosaic have shrunk or grown,” Kavanaugh says, “we might be able to help inform decisions about marine ecosystem management across international waters and the high seas.”
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