Look at this tiny wonderland of delicate, star-shaped, fair-haired anemones – benignly filtering food from the water and setting a lovely ocean ambiance. They could be little whisks that a mermaid might use to make a soufflé. Peaceful, right? Wrong. These dudes are remorseless, parasitic death-bringers who drill into their hosts and eat all their food. Which makes me love them a lot, really.
These lined sea anemones (Edwardsiella lineata) spend part of their lives anchored to the bottom of the ocean, doing what most anemones do, sitting around and eating what the current brings them. Before that, however, when they are but wee larvae, they go on a search-and-destroy rampage of their favorite host, a ctenophore known as the sea walnut, or warty comb jelly. We have lots of ctenophores in New England – you can see them in action in this short video by Alex Shure. Ctenophores may seem pretty hardy in this big swarm, but they are no match for the larval lined sea anemone.
It’s not just what this tiny assassin does, it’s how. Mayhem is a polite word for it. As Casey Diederich, my favorite marine biologist for fact-checking blogs about demented goings-on in the ocean, points out:
“The parasitic larva kind of hangs out in/near the pharynx, part of the digestive cavity of the ctenophore, to steal its food. This means that it must have some way to evade digestion by the ctenophore. If you could evade digestion, why not just enter through the ctenophores mouth? Apparently, the parasitic larva burrows through the outside of the ctenophore, then migrates through the ctenophore’s mesoglea (the “jelly” found in jellyfish, ctenophores, and other kinds of marine invertebrates), and canal system until it gets to the ctenophore’s gut/pharynx. WHAT??? Nature is a crazy motha.”
And, yes, “crazy motha” is a technical marine biology term.
This is probably not much fun for the ctenophore, which can play the unwilling host to several of these baby anemones at a time, but it’s not all bad news, depending on your perspective.
First of all, the parasitic infection prevents the comb jelly from thriving, and thus reduces its population over time. Ctenophores eat zooplankton, including tiny juvenile fish, like cod and flounder. So it’s possible that the parasitic action of the anemone is helping more of these little fish not get eaten and make it to adulthood. More food for us! In some places over half the local comb jellies are infected with the parasitic anemone.
Secondly – in the northeastern Atlantic, off the coast of Europe, these comb jellies are invasive, and really taking a toll on the native wildlife, so the lined anemones might be preventing even worse devastation to the fisheries in that neck of the ocean.
So, the anemones are the good guys? Well, hold on. The larval form of the lined anemone has been implicated as one of the animals that can cause the annoying “sea-bather’s eruption” – an itchy rash you get sometimes after you swim in the ocean. Also, given how successful they are at life in general, there is concern that the lined anemones themselves might become an invasive nuisance in the northeastern Atlantic.
I guess there are no easy conclusions to draw here. Still, I think it’s safe to say that if these types of animals had blood, the lined anemone’s would be cold. One cold-blooded, crazy motha.