School of Aquatic and Fishery Sciences

Warming events are increasing in magnitude and severity, threatening many ecosystems worldwide. As the global temperatures continue to climb, it also raises uncertainties as to the relationship, prevalence, and spread of parasites and disease.

A recent study from the University of Washington explores the ways parasitism will respond to climate change, providing researchers new insights into disease transmission. The paper was published in May in Trends in Ecology and Evolution.

The review builds upon previous research by adding nearly two decades worth of new evidence to build a framework showing the parasite–host relationship under climate oscillations. Traditionally, climate related research is done over long time scales, however this unique approach examines how increasingly frequent “pulse warming” events alter parasite transmission. 

“Much of what is known about how organisms and ecosystems can respond to climate change has focused on gradual warming,” said lead author Danielle Claar, a postdoctoral researcher at the UW School of Aquatic and Fishery Sciences. “Climate change causes not only gradual warming over time, but also increases the frequency and magnitude of extreme events, like heat waves.”

Claar explains that both gradual warming and pulse warming can and have influenced ecosystems, but do so in different ways. Organisms may be able to adapt and keep pace with the gradual warming, but an acute pulse event can have sudden and profound impacts.

The 2013-2015 “blob” is one such extreme heat pulse event which has been linked to a massive die-off of sea stars along the Pacific coast of the U.S. and Canada. Many species of sea stars, including the large sunflower sea star, were decimated by a sudden epidemic of wasting disease. Five years later, populations in the region are still struggling to recover. The abnormally warm waters associated with the blob are thought to have favored the spread of the sea star-associated densovirus, the suggested cause of the disease.

The authors compare the prevalence of these marine diseases to a rising tide, an ebbing tide, or a tsunami. Disease transmission can rise or ebb in concert with gradual warming or a series of pulse warming events. However, a severe pulse warming event could result in a tsunami, “initiating either a deluge or drought of disease,” as was observed with sea stars along the Pacific Northwest.

However, not all pulse heat events will cause the same response. What may benefit a particular parasite or host in one system can be detrimental in another. Warming can alter a parasite’s life cycle, limit the range of suitable host species, or even impair the host’s immune response. Some flatworms which target wildlife and humans cannot survive as long in warmer waters, decreasing their window for infecting a host. Another recent UW study shows parasites commonly found in sushi are on the rise with their numbers increasing 283-fold in the past 40 years, though the relationship between heat pulse events and their abundance is not yet clear.

“The relationships between hosts, parasites, and their corresponding communities are complex and depend on many factors, making outcomes difficult to predict,” said Claar, who recommends researchers make predictions on a case-by-case basis for their individual systems.

The authors conclude that rather than a straightforward tidal prediction, they would expect pulse warming to cause “choppy seas with the occasional rogue wave.”

“It is important that we are able to understand and predict how parasitism and disease might respond to climate change, so we can prepare for, and mitigate, potential impacts to human and wildlife health,” said Claar.

The paper’s co-author is Chelsea Wood, a UW assistant professor of aquatic and fishery sciences.

This research was supported by the NOAA Climate and Global Change Postdoctoral Fellowship Program, administered by UCAR’s Cooperative Programs for the Advancement of Earth System Science (CPAESS); the US National Science Foundation; a Sloan Research Fellowship from the Alfred P. Sloan Foundation; a UW Innovation Award from the UW President’s Innovation Imperative; and a UW Royalty Research Fund Award.

Grant numbers: NA18NWS4620043B (CPAESS), OCE-1829509 (NSF)

For more information, contact Claar at danielle.claar@gmail.com. 

Plastic pollution is an increasingly present threat to marine life and one which can potentially impact your dinner table.

Oysters, and other economically valuable shellfish, filter their food from the water where they may also inadvertently capture tiny microplastics. The ingestion and accumulation of these microplastics can have detrimental effects on their health and may be passed to other animals, including humans, through the food chain.

In a recent interdisciplinary study, University of Washington researchers at the School of Aquatic and Fishery Sciences, Department of Chemistry and Department of Materials Science and Engineering used advanced methodologies to accurately identify and catalog microplastics in Pacific oysters from the Salish Sea. They have discovered that the abundance of tiny microplastic contaminants in these oysters is much lower than previously thought. The findings were published in January in the journal Science of the Total Environment.

“Until now, not a lot of chemical analysis has been done on microplastics in oysters,” said co-author Samantha Phan, a UW doctoral student in chemistry. “The microplastics that chemists have looked at in previous studies are slightly bigger and easy to visually recognize, but with oysters, the microplastics are much smaller and harder to identify.”

In their study, the team sampled wild Pacific oysters harvested from Washington’s state parks throughout the Salish Sea. Using standard processing methods, the oysters’ tissue is dissolved and the remaining solution is passed through a filter. The filter collects all of the possible microplastic particles.

“Observation of filters is the method researchers have typically used, so if we had stopped there, we would have thought all the oysters had microplastics because small particles were present in most of the filters,” said lead author Julieta Martinelli, a UW postdoctoral researcher at the School of Aquatic and Fishery Sciences.

Martinelli’s initial observations under a dissecting microscope revealed what were thought to be high numbers of microplastics left behind in the testing filters, but when Phan further analyzed those filters with three advanced chemical identification techniques, they realized that most of what was left in the filters was not actually plastic.

“When we’re characterizing plastics, or any polymers in chemistry in general, we have to use multiple techniques, and not every technique will give you a full picture. It’s half a picture or just part of the picture,” said Phan. “When you put all those pictures and characterizations together, you can have a more complete understanding of what the composition or identities of these particles are.”

During their analyses, the team realized that many of the particles were, in fact, shell fragments, minerals, salts and even fibers from the testing filters themselves. In the end, they found that only about 2% of the particles distilled from the oysters could be confirmed as plastics.

“Most people so far have not used the combination of techniques or instruments that we used,” said Martinelli. “It’s really easy to stop at the first part and say, ‘Oh, there’s a lot of particles here. They look like plastic. They must be plastic.’ But when you actually go deeper into the chemical composition, they might not be.”

The number of plastic particles that the team found was relatively low compared to the total number of particles analyzed; however, they stress that while it appears Pacific oysters are not accumulating large amounts of plastic, they could not identify 40% of the particles observed due to technical limitations. The researchers also acknowledge that while using a combination of instruments is the most complete way to analyze these particles, access to the equipment, elevated costs and the extremely time-consuming nature of the work are limiting factors for widespread use.

As suspension feeders, oysters pull in water and the particles present in it when they inhale. Particles are then sorted in and out of the animal through their gills. Previous experiments have shown that when oysters are given microfibers or microbeads, they expel the majority of them either immediately or after a few hours. The hypothesis is that oysters’ gill anatomy and physiology might be the reason why the team did not see large amounts of plastic accumulation in their samples.

“A lot of this has to do with how the oysters process water through their gills and how they get rid of particles,” said Martinelli. “It doesn’t mean microplastics are not in the water, it means that the animals are better at expelling them.”

In agreement with this, it has been suggested that suspension-feeding bivalves like oysters might not be good indicators of pollution in estuaries because they naturally expel microplastics instead of ingesting them, which is good news for consumers that like eating oysters.

Other co-authors are Christine Luscombe, a UW professor of materials science and engineering, and Jacqueline Padilla-Gamiño, a UW assistant professor of aquatic and fishery sciences.

This research was supported by NOAA-SK and the Royal Research Fund awarded to Padilla-Gamiño. Part of this work was conducted at the Molecular Analysis Facility, a National Nanotechnology Coordinated Infrastructure site at the University of Washington supported in part by the National Science Foundation, the University of Washington, the Molecular Engineering & Sciences Institute and the Clean Energy Institute, and the Washington Research Foundation.

For more information, contact Martinelli at julimar@uw.edu and Phan at samphan@uw.edu.

This release was written by Dan DiNicola of the School of Aquatic and Fishery Sciences.

Grant number:  NNCI-1542101 (NSF)

By John Meyer
This story originally appeared on the UW College of the Environment website

In a world where valuable natural resources can be scarce, nature often loses when humans set their sights on something they want. But a new study published in the journal Ecological Applications shows that doesn’t always have to be true. Researchers found that with proper management of salmon fisheries, both humans and bears — who depend on a healthy supply of the fatty, oily fish — can thrive.

“We hear lots of stories about how fishing is decimating our oceans, and how humans are competing with wildlife,” says lead author Alexandra Lincoln. “This gives us some optimistic news instead, and highlights that if we have enough data to carefully manage fisheries and healthy habitat, we can manage a fishery to meet the needs of both wildlife and people.”

Building on a nearly two decade-long dataset, Lincoln and her colleagues looked at the relationship between wild brown bears and their staple food source, sockeye salmon in Alaska’s Wood River and Iliamna Lake watersheds. This vast network of forests, mountains, streams and rivers empties into Bristol Bay to support its world-famous salmon fishery. With intense fishing pressure on this delectable ocean-going fish, the question of whether enough fish return to the system to not only spawn — critical for supplying the next generation of fish — but also feed hungry bears is critical. Good news according to the data: yes, there is.

One of the study’s key findings shows a repeating pattern over the years of bears reaching a saturation point in terms of feasting on salmon. In other words, researchers found that bears often reach a point of satiation, and that adding more fish into the system doesn’t translate to bears eating more. And because there is no shortage of fish, the bears in many cases eat only the high energy good stuff, like the brains, bellies, eggs or the giant hump that develops on the backs of male sockeye during spawning.

“I was surprised at how regular that pattern of saturation was,” says Lincoln. “Seeing how picky these bears can be and all the leftovers, it’s hard to believe that bears would be starving and leave all these fish bits everywhere.”

It’s important to note that scientists did not see satiation occur in all years, but that doesn’t necessarily mean the bears go hungry. “Bears often forage in areas containing several adjacent spawning streams, allowing them to move back and forth among neighboring streams over the course of a day or two,” says Aaron Wirsing, professor of environmental and forest sciences and a project lead. “Thus, bears without enough food on one stream often have better fishing options nearby.”

The Wood River and Iliamna Lake watersheds are a rare place where scientists can isolate the effects of fish harvest on the health and wellbeing of bears. The watershed is relatively untouched and massive, and the study sites scientists visit are not shared by other salmon species besides sockeye. Brown bears are the major top predators in the region as black bears and wolves are rare. With only one dominant salmon species, and one dominant predator, scientists can determine cause-and-effect more precisely than in other systems where they may be other complexities.

“We can’t apply all of what we’ve learned to all systems,” says Lincoln. “This fishery is data rich” which isn’t always true for other heavily managed ecosystems that produce goods that people want. That wealth of data contributes to the success of what is regarded as one of the best managed fisheries in the world — the Bristol Bay Sockeye Salmon Fishery — and continued data collection gives researchers the ability to use decades-old data to connect management to parts of the ecosystem like brown bears.

Scientists from UW and elsewhere have been studying these watersheds for over 70 years through the Alaska Salmon Program, and collecting brown bear data for nearly 20. Under the direction of Tom Quinn, a professor of aquatic and fishery sciences and one of the Alaska Salmon Program’s lead scientists, researchers walk several creeks every day during spawning season counting salmon. They count alive fish, dead fish and fish that have been killed by bears or seagulls. They note the condition of the salmon carcass — is there just a bite of the belly, or has nearly the entire animal been consumed? This level of detail, and the time series over which the data were collected, was key to uncovering the insights they published. “Leveraging two decades of work offered us a unique opportunity to explore patterns of bear predation in relation to the ebb and flow of salmon availability,” notes Wirsing.

“Over the 20 years, we’ve counted something like 325,000 dead fish,” says Lincoln. “Some days we’ll count 10,000 live fish in a stream 2 km long. Seeing a stream chock full of fish, with wall-to-wall red salmon backs sticking out of the water, is a highlight of this work.”

Lincoln received her master’s degree at the UW School of Aquatic and Fishery Sciences working on bear-salmon interactions in Alaska, and now brings her expertise working as a senior ecologist with King County.

Get a feel of what it’s like to be a scientist collecting data in the salmon streams of the Wood River watershed in UW’s previously published story A Living Laboratory.