Millions of non-native creatures known as pyrosomes are “blooming” off the coast of British Columbia and have the potential to devastate an already fragile food chain.
Scientists in Canada know very little about the pimply, translucent, tube-like animals — normally found in the tropics —some of which grow to 10 metres in length.
“There’s pictures of people swimming up to these, riding on them as a diver, sticking their head in the opening,” said Moira Galbraith, a zooplankton taxonomist at the Institute of Ocean Sciences in Sidney, B.C.
The University of Victoria’s Ocean Networks Canada encountered a large swarm of pyrosomes earlier this week.
Rapid reproductive ability
The specimens that have made their way north have been much smaller in size, ranging from eight to 60 centimetres in length.
Pyrosome means “fire bodies,” referring to the creature’s bioluminescence.
The mucous-covered animals turn from plump and juicy to flat and pancake-like when handled or left out of the water for more than a few hours.
For all their oddness, it’s the sheer number of them that has both biologists and fishermen boggled.
A research team in central Oregon reported gathering an estimated 60,000 individual pyrosomes in around five minutes of trawling with a net.
“It’s kind of crazy, it’s a little bit over the top,” said Galbraith, who has a theory that the creatures arrived after becoming stuck in anomalous warm water currents that occurred in the eastern Pacific between 2014 and 2016.
“Right now, these are only visitors, not an invasive species, yet,” Galbraith said. “They are here for now, until the currents take them elsewhere.”
The firm, cucumber-like creatures are actually made up of thousands of individuals that can reproduce asexually by cloning themselves and forming colonies in the shape of hollow tubes.
They also have the ability to reproduce sexually and form entirely new organisms, meaning they have two methods of rapid reproduction.
Galbraith said it remains to be seen if they will be able to reproduce effectively once the water returns to its regular temperature.
Food chain threat
The gelatinous filter feeders eat microorganisms called zooplankton, which also support populations of shrimp, crab, mollusks and other filter feeders.
Among these are crustaceans, which are essential, high-protein food sources for local fish and seabirds.
If the nutrient-poor pyrosomes out-compete nutrient-rich crustaceans, it could severely upend the food chain from crustaceans right up to salmon and humpback whales.
Meanwhile, local fishermen who are gearing up for the commercial salmon season worry they’ll be hauling in hundreds of kilograms of worthless pyrosomes instead of the lucrative fish stocks.
Washington-based skipper Dobie Lyons has been pulling them out of the Juan de Fuca Strait by the dozens on hooks set for halibut since that fishery opened in April.
“If we start pulling these in our gill net, we’re probably going to have thousands and thousands and that’s what we’re worried about,” said Dobie.
He said fisherman have been finding pyrosomes in the bellies of black cod, suggesting the creatures aren’t just floating around mid-depth but also covering the ocean floor where black cod feed.
The first time he pulled them out of the water he wasn’t sure what to do and even worried they might be poisonous.
“We were kind of scared of them at first, afraid to touch them,” he said.
Now, having handled countless numbers of the organism, he just tosses them back in the water and continues fishing.