In 2014, Long Live the Kings, a non-profit organization devoted to Pacific salmon restoration and recovery, received a grant to begin what biologists hoped would be a long-term zooplankton monitoring project in Puget Sound. The project would involve tribal governments, universities, state agencies, federal agencies, and other non-profits. “It was quite the undertaking, given that there are so many partners and stakeholders,” says Julie Keister, a biologist at NOAA who now helps oversee the program. “It was a reflection not just of how important zooplankton are to Puget Sound, but also how not a lot was known about them.”

Plankton form the sprawling base of every conventional marine food web. They are divided into two general types. Phytoplankton are, in essence, plants; they are at the very bottom of the food web, or the lowest trophic level. Zooplankton, as organisms that eat phytoplankton, sit just above them. Zooplankton can be small animals, like copepods; or younger life stages of what will eventually grow to become larger, more visible animals like crab or shellfish larvae. As such, most zooplankton are microscopic, but some, like jellyfish, are so large that they can be seen quite easily.

The word plankton comes from planktos, which is Greek for “wanderer”; and plankton in general are marked by a certain tendency to drift, or wander, going as they do largely where the tides or currents take them. But rather than being mere passive drifters, zooplankton are particular organisms in their own right. Many can swim up and down in the water to help control the direction they drift. Some do well in warmer water, and others thrive in cold. Some are large and fatty (relatively speaking), while others are smaller and comparatively less nutritious.

In 2015, the first year of The Blob, rather than becoming a zooplankton desert, Puget Sound was full of copepods and other organisms.

Where zooplankton become vital is that they themselves are then eaten by a host of species, including some that humans care a lot about, like young salmon. The purpose of the monitoring project, then, was to see how the zooplankton’s ups and downs played out in the more or less confined spaces of Puget Sound. The approach would be straightforward conceptually if not logistically. Every year, teams of biologists would do biweekly zooplankton surveys from the spring through the fall, at points from the San Juans down to South Sound. By lowering a net to within a few meters of the bottom and drawing it to the surface, they would be able to characterize Puget Sound’s zooplankton community, seeing how it varied in space and time.

The monitoring project is ongoing, but that was not always assured. After the initial grant to Long Live the Kings ended in 2016, it was not at all clear the program would survive. That it does is thanks to funding from the Environmental Protection Agency distributed through a consortium of state agencies known as the Habitat Strategic Initiative Lead. Funds from that program allowed the project to transition to the Washington Department of Fish and Wildlife (WDFW), which will steward it going forward. And in April, some results of the survey work were published in the journal Progress in Oceanography. There, the authors took advantage of their dataset to see how Puget Sound’s zooplankton community responded to The Blob, as the large marine heatwave that affected the northeastern Pacific from 2014 through 2016 has come to be called.

“It appears that a lot of what is happening in Puget Sound is affected by local processes, rather than necessarily mirroring what’s happening on the coast. That was our really big takeaway.” -- Amanda Winans, UW School of Oceanography 

The Blob was a massive event. At its peak, more than one million square miles of the north Pacific were affected, and to a depth of up to three hundred feet. Its ecological effects were profound and are still being investigated. But with such a wide area to consider, scientists sometimes have to rely on a kind of geographic shorthand. “Most efforts to study and characterize The Blob’s effects in the California Current system have been on the outer coast,” Keister says. “What happens out there obviously influences what happens in the inland waters, but these data gave us a chance to focus more on Puget Sound and the Salish Sea.” 

For their paper, the authors focused on 2015 and 2016, when The Blob most greatly affected the inland waters, and considered the regional zooplankton community at the intersection of time, space, and climate. What they found was a marine space full of complexity and surprises. Levels of chlorophyll, for instance—an indicator of phytoplankton levels, or how much food was available to zooplankton—did not show a consistent relationship with temperature, being fairly high in 2015 before becoming patchier in 2016.

Where zooplankton were concerned, there were anomalously high increases in their biomass across the entire Puget Sound. In 2015, the first year of The Blob, “It was across the board,” says Amanda Winans, a research scientist in the University of Washington School of Oceanography who was lead author on the paper. Rather than becoming a zooplankton desert, Puget Sound was full of copepods and other organisms. These increases persisted through 2017 in southern Puget Sound sites, but not in northern sites in the Strait of Juan de Fuca. Copepod species in Puget Sound that favor warm water did well throughout, while species that prefer cooler water, and thus tend to be larger, did not. (“That, at least, was not a big surprise,” Winans says.)

“This increase in zooplankton contrasted with reports of many coastal populations, especially in the [California Current System] where total biomass generally decreased during the [marine heatwave],” the authors wrote. Why the patterns in Puget Sound differed from those on the outer coast is not entirely clear, although there are some clues. The Salish Sea Model, for instance, suggested that freshwater inputs into Puget Sound were much higher in 2015, which in turn increased the exchange flow and brought more nutrients into the inland waters from the outer coast, leading to greater amounts of phytoplankton. Additionally, the warmer temperatures experienced in Puget Sound during The Blob may have spurred growth for resident zooplankton, which were able to gorge on those phytoplankton.

“It appears that a lot of what is happening in Puget Sound is affected by local processes, rather than necessarily mirroring what’s happening on the coast,” Winans says. “That was our really big takeaway.”

The work for the recent paper ties in with a study Keister published last fall, looking for links between climate, zooplankton dynamics, and survival patterns of Chinook and coho salmon in the Strait of Juan de Fuca, which is at the northern terminus of Puget Sound. In that study, she and her co-authors showed that zooplankton communities had strong seasonal patterns, alternating between species that were present in Puget Sound (which tended to be smaller) and others brought in from the outer coast (which tended to be larger). Juvenile salmon tended to do better when zooplankton communities were dominated by outer coast species—precisely the kind that did not fare so well during The Blob.

“People had been making assumptions about how Puget Sound food webs would operate based on coastal observations,” she says. “This study shows that Puget Sound is actually quite different.” Continuing the zooplankton survey for years to come will be crucial in this regard; that it is now housed in WDFW could help it stretch on indefinitely. “That’s one of the key takeaways from this work,” Keister says. “To understand Puget Sound, you have to study Puget Sound.”

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This article has been funded wholly or in part by the United States Environmental Protection Agency under assistance agreement PC-01J22301 through the Washington Department of Fish and Wildlife. The contents of this document do not necessarily reflect the views and policies of the Environmental Protection Agency or the Washington Department of Fish and Wildlife, nor does mention of trade names or commercial products constitute endorsement or recommendation for use.