The hydra effect — your new world for the day:
New research suggests that sometimes trying to completely eliminate a
problematic non-native species may cause more harm than good.
Wherever green crabs (Carcinus maenas) land, scientists have documented them
decimating food webs by devouring benthic invertebrates that provide
nourishment for shorebirds, fishes and other species. Over the years, they have
eaten their way onto a list of the world’s top 100 most unwanted species
<http://www.issg.org/pdf/publications/worst_100/english_100_worst.pdf>.
Along the way the scientists made a surprising discovery that they believe
could change how managers deal with other invasive aquatic species.
San Francisco area project: ...2009 to fewer than 10,000 by 2013. “We were
feeling very good with ourselves,” he says, “But then suddenly the population
exploded, and we were faced with even more crabs.”
By 2014 the number of green crabs in Seadrift Lagoon shot up to an alarming
300,000. Other nearby bays didn’t experience a similar population explosion,
leaving the researchers wondering what the heck could have caused it.
The reason why they believe the population took off? Quite simply, green crabs
are cannibalistic. Adults keep the population in check by eating some of the
youngsters. But traps to eradicate the crabs caught only the adults, which left
a slew of uneaten offspring ready to grow big and strong.
Given time things could have gotten even worse, as a female green crab that
reaches maturity can produce up to 185,000 eggs.
“The results of this study provide an urgent warning to those involved in the
management of invasive species,” they write in a new study
<https://www.pnas.org/content/118/12/e2003955118> in the Proceedings of
National Academy of Sciences.
Bigger Lessons
The factors that led to the population explosion — known as the hydra effect —
aren’t unique to European green crabs. It could happen with other aquatic
species, too, says Grosholz, including almost all crabs, lobsters, shrimp, and
even a number of fishes.
And it’s not just species that eat their young, either. “You can see this
response in any species where the adults consume a lot of the resources that
their offspring might use,” he says.
Doing the Work
Having that data is a critical first step. That’s where community scientists
<http://calag.ucanr.edu/archive/?article=ca.2021a0006> can come in, he says.
“We have throughout this [work in California] relied on volunteers to help pull
the traps and count the crabs. We put out 90 traps a day and pull in thousands
of crabs a day,” he says. “Volunteers were really instrumental in reaching our
goals for the project. And now they’re really instrumental in maintaining this
low population level.”
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FULL ARTICLE LINK - Very interesting. YUM, green crabs!
https://therevelator.org/invasive-green-crabs/
shirley johnson
thusone@xxxxxxx
