Invasive, Blood Sucking Parasites on Shrimps Continue Moving Northward

An invasive species of blood-sucking parasites on mud shrimps have been discovered in the waters surrounding Calvert Island, British Columbia, in Canada, marking the northernmost recorded presence of the parasite on the West Coast and suggests its expansion without human-based transport methods.

Orthione griffenis, an isopoda parasite - related to woodlice - originally native to Asia and Russia, has migrated to North American waters. According to the Florida Museum of Natural History, these "cough drop-sized" crustaceans have adversely affected the population of mud shrimps in Washington and California for the past three decades, citing that these parasites have caused the collapse of the mudflat ecosystems.

Researchers from Hakai Institute and Florida Museum of Natural History have submitted their reports in the journal BioInvasions Records.

Poleward Expansion of O. griffenis

By the early 2000s, the expansion of O. griffenis had already reached as far as Vancouver Island, also in British Columbia. This new discovery from the Hakai Institute notes a northward expansion of more than 180 miles.

The mud shrimp parasite, a bopyrid isopod, was discovered by the researchers in the summer of 2017. It was found among the population of mud shrimps, Upogebia pugettensis, in Central British Columbia, Canada. In their estimates, 25 percent of susceptible mud shrimp hosts on the area's Calvert Island were parasitized by summer 2018 and winter 2019. They note that while the discovery confirms the presence of the O. griffenis in a location farther north than previously established, the prevalence around Calvert Island is less than the other, previously known invasive range of the parasite.

In the report, the O. griffenis has a planktonic larval phase which suggests that its northward expansion is not entirely due to boat traffic.

"I was on the lookout for things that seemed out of place," said Matt Whalen, a postdoctoral researcher at the University of British Columbia, adding that "this particular parasite wasn't initially on my radar."

Even Without Human Intervention

Most scientists believe that O. griffenis was brought to foreign areas because of human activities. It first arrived in North American waters from East Asia by being carried through the ballast water in traveling ships. However, their appearance at Calvert Island proves that humans are not the only means for their invasion of other waters.

"During the bio blitz, one of the things we talked about was that there were no invasive species at all. And then we found this thing," said Gustav Paulay, co-author of the study and invertebrate zoology curator at the Florida Museum of Natural History.

Whalen said: "It's a bit depressing because we tended to associate this parasite with places that have a lot of marine traffic and aquaculture, like California and Oregon." He added that given the parasite's life cycle, preventing its further spread is hard to prevent.

The bopyrid isopod O. griffenis starts to hitch on planktonic copepods, serving as its intermediate host during the pre-adult stages. Later on, they search for shrimp blood and do so by attaching itself into the gills of mud shrimps. They drain blood and nutrients from the mud shrimps, leaving them weak and even unable to reproduce.