I didn’t know this before, but apparently in Britain, American signal crayfish is an invasive species. For a while, the go to method to tackle this problem is to trap, cook, and eat them (as popularized by celebrity chefs).  

It does seem logical, plus it’s also beneficial to us humans because we get to eat a lot of crustacean without having to worry about the ecosystem and everything. Free freshwater lobsters, right? 

However, a new research by UCL and King’s College London shows that this method doesn’t make the problem go away. 

Published in the Journal of Applied Ecology, the researchers found that crayfish trapping is ineffective in determining and controlling the species, as most of them are too small to catch using standard baited traps. 

Even though trapping has become a popular way to potentially control this invasive species, scientists warn that it may make the problem worse. It unintentionally makes people spread the species to new habitats and greatly increases the risk of accidental catches of the strictly protected native species. 

Co-author Eleri Pritchard said, “Invasive signal crayfish from the US were introduced to England in the 1970s. Since then they have spread rapidly, displacing native crayfish, impacting fish and damaging ecosystems,” 

“While celebrity chefs and conservation charities have, with good intentions, promoted trapping and foraging as a way to control American signal crayfish, our research shows trapping to be ineffective. We are also concerned that trapping risks spreading the fungal pathogen, called crayfish plague, which is lethal to native European crayfish.” 

The tiny crustaceans 

Taking place in an upland stream in North Yorkshire, researchers compared the effectiveness of three methods used for surveying population numbers: baited funnel trapping, handsearching, and triple drawdown technique.  

The last method drains a short section of stream in a carefully controlled way and calculate the number of crayfish that are there, including infants. 

To measure effectiveness, scientists compared all methods for determining population size, and for understanding the prevalence of crayfish invasion and the ecological impact. 

Through the triple drawdown technique, researchers could determine crayfish populations more accurately. They’ve identified signal crayfish densities up to 110 per sqm (10.7 sqft). That’s a lot more than previous estimates by trap sampling. 

This new technique also showed that most of the crayfish caught were smaller than a penny coin (1.9 cm or 0.74 inch). Only 2.3% of the population large enough to be caught in standard traps. 

More importantly, signal crayfish can become sexually mature before reaching a ‘trappable’ size. This allows the populations reproduce despite the trappings. 

Less trapping more educating 

Crayfish expert and co-author Paul Bradley said, “We now have strong data to show that trapping does not help to control invasive crayfish. On the contrary, there is growing evidence that trapping furthers the spread,” 

“In the short-term, conservation efforts should re-focus on promotion of aquatic biosecurity, and in the longer-term we need further research to better understand the invasion biology of American signal crayfish,” 

“This will help to inform more effective and sustainable approaches to the management and control of this problematic invasive species.” 

Scientists strongly recommend to reduce recreational crayfish trapping in order to prevent the further spread of the invasive species. They believe that the focus should be on initiatives like UK’s national Check Clean Dry campaign. 

It aims to educate people about how non-native invasive aquatic plants and animals can be transported between waterbodies on contaminated clothes and equipment as well as by fish stocking and water transfer schemes. 

“Signal crayfish have a devastating impact on our waters, harming fish populations, increasing economic costs for fisheries and causing a nuisance for anglers,” said environment manager at Angling Trust Dr. Emily Smith. 

“These findings present a new chapter in management practices, providing invaluable intelligence for fisheries and angling clubs, supporting them in refining practical solutions to controlling this highly aggressive species,” she added. 

I guess there will be less binge eating crayfish after this. But if it helps the ecosystem (the not eating part), I think it’s not a problem. 

Shrimp populations decline due to parasite 

I adore isopod, the giant one, that is. The other, tiny, parasitic ones? I say nay times infinity.  

Well, a species of isopod called Orthione griffenis, native to Asia and Russia, has decimated mud shrimp populations in California and Washington over the past 30 years. British native crayfish isn’t the only species in danger here. 

The parasite has caused the collapse of mudflat ecosystems anchored by the shrimp. In the 2000s, the parasite reached Vancouver Island. A new study found O. griffenis at Calvert Island, representing the parasite’s population growth of more than 180 miles. 

It was during a 2017 bioblitz (period of biological surveying) that the scientists found these parasitic crustaceans. Hakai postdoctoral researcher and study lead author Matt Whalen said, “I was on the lookout for things that seemed out of place. But this particular parasite wasn’t initially on my radar.” 

Before, most scientists believed that the parasites spread through human transport. O griffenisis are thought to have first arrived in North America by traveling in ships’ ballast water. 

But with their appearance at Calvert, 150 miles from the nearest city of more than five thousand people, apparently they don’t need human interference. 

Co-author Gustav Paulay said, “This is such an astonishingly spectacular part of the planet. During the bioblitz, one of the things we talked about was that there were no invasive species at all. And then we found this thing.

Whalen said that this finding is a bit depressing. “We tended to associate this parasite with places that have a lot of marine traffic and aquaculture, like California and Oregon,”

“Finding them on Calvert Island really suggests that there’s very little preventing the spread because of the parasite’s life cycle.” 

Bopyrid isopod vs mud shrimp 

In the pre-adult part of this crustacean’s life, it hitches a ride on planktonic copepods. This allows the parasite to travel to new and far-flung mudflats in search of shrimp blood. 

As adults, the isopods then attach to the gills of another crustacean host, mud shrimps in this case. After that, they take everything away from the shrimps.  

These isopods are so brutal that the mud shrimps which are infected can’t reproduce because they lack the required energy to do so. “They’re essentially castrated,” said Paulay. 

Now, mud shrimps are sort of weird, I mean to me they’re like crayfish but weirder. Even though they’re not attractive, these crustaceans play a big role as as environmental engineers in the mudflats of the Pacific Coast. 

Mud shrimps cycle nutrients when they filter food, pumping oxygenated water into an expansive network of tunnel dwellings, which provide housing for a suite of creatures, including gobies, worms, clams and other shrimp species. 

In their healthy states, these shrimps’ presence affects how the entire mudflat ecosystem functions. 

Whalen said, “The infection rates on Calvert Island were higher than I would’ve anticipated, about one in four hosts were parasitized. That’s a pretty good chunk of the population.” 

Tracking for now 

We still don’t know if the researchers have found a way to solve this parasite invasion. But we know that they’re tracking the northward spread of the parasite. 

O griffenisis’ rapid spread on Calvert Island shows that it may only be a matter of time before it reaches the North Coast of British Columbia and moves onward to Alaska, the upper edge of the mud shrimp’s range. 

According to Paulay, the discovery of this parasite underlines how marine bioblitzes can function as early warning systems for invasions. “Every bioblitz we do, we find invasive species. If you catch them early enough, you have a chance to do something about it,” he said. 

 

Sources

https://www.sciencedaily.com/releases/2020/10/201013090249.htm

https://www.sciencedaily.com/releases/2020/09/200917180405.htm