SEATTLE — During recent marine heat waves, millions of gelatinous, pickle-like filter feeders washed up on West Coast beaches.
Little has been understood about how the population explosion of the seemingly alien creatures, called pyrosomes, affected life in the Pacific Ocean.
But a new study shows the proliferation of the animals might have sucked up precious energy from the food web, likely affecting fish and animals higher up in the food chain.
The study by Oregon State University researchers working with the National Oceanic and Atmospheric Administration analyzed how a model of the ocean food web changed before and after recent marine heat waves.
The study found that the heat wave had wide-ranging effects on the movement of nutrients and energy in the Pacific Ocean, with pyrosomes absorbing much of the energy. The results are significant since the models suggest that most of the redirected energy to pyrosomes did not go on to feed other species.
In the last decade, the Northern California Current marine ecosystem, which extends from Vancouver Island in Canada to Cape Mendocino in California, has experienced a period of abnormally warm temperatures.
In 2014, a particularly intense marine heat wave brought temperatures roughly 5 degrees Fahrenheit above normal and was dubbed “The Blob,” for its appearance on satellite temperature maps. According to NOAA, that heat wave continued until mid-2016, and abnormally warm temperatures have occurred in the North Pacific nearly every year since 2019.
Since then, regional research and studies have documented a decline in salmon runs, die-offs of sea birds and harmful algal blooms that closed Dungeness crab fisheries, all related to marine warming. The study from Oregon State University is one of the first to comprehensively analyze the heat wave’s effects across the entire food web from the smallest phytoplankton and detritus on the seafloor to whales, fish and seabirds, said co-author Dylan Gomes.
“What this showed us is that these heat waves impact every predator and prey in the ecosystem through direct and indirect pathways,” he said.
Researchers compared two “end to end” ecosystem models, one populated with data from 1999 to 2012 and one from after the onset of the marine heat wave in 2014 until 2022. Researchers estimated the biomass for 86 different organism groups with data from NOAA sampling and commercial and recreational fisheries, satellite information on phytoplankton and other studies.
Comparison of the two models showed which organisms received more and less energy, and found pyrosomes were by far the greatest benefactor while other species, like jellyfish, sardines, cod and certain types of sea snails and slugs, lost out.
Until the onset of the 2014 heat wave, pyrosomes had never been detected in 25 years of NOAA surveys, Gomes said. Each cylindrical pyrosome, which have been found to be up to 3 feet long, is a colony of tunicates a few millimeters long, he said. Pyrosomes are typically found farther south and are free-floating filter feeders consuming phytoplankton.
“They went from being zero — completely absent as far as anybody knows — to being one of the most abundant things in the entire ecosystem,” Gomes said.
According to the study, pyrosomes have been considered “trophic dead ends” since they have low energy content and most of them end up as detritus. It’s not clear how nutritious they are to the species who have consumed them in recent years, Gomes said, which means species further up the food chain, from the fish caught commercially to marine mammals, have likely been affected.
“That has an impact on the entire ecosystem … the pyrosome is consuming energy that normally would have gone through multiple prey to eventually end up in a salmon,” he said.
With global climate change, marine heat waves are expected to increase in frequency and intensity, but what exactly the next few years will look like for the Northern California Current is unclear, Gomes said. The study takes a “first stab” at the impacts of the heat wave by looking before and after 2014 but does not predict what the food web could look like if temperatures were to return to normal or how the food web has changed in between periods of heat since 2014, he said.
“The take-home here for people and food security is that we want to know how fishery resources are shifting so we can better manage our oceans. We don’t want to deplete our resources. We don’t want to make any ecosystems collapse,” Gomes said.
The model and research was made possible by detailed ocean surveys and investments by NOAA and other scientific organizations, which are not available in other countries near oceans, he said.
Gomes is a biologist with the U.S. Geological Survey and was previously in a postdoctoral position with the Marine Sciences Center at Oregon State University. OSU assistant professor Joshua Stewart was a co-author of the study.
