Nature Blog Network

Sunday, April 13, 2008

Cthe Ctenacious Ctenophore

Once there was a sad jelly

The jelly felt sorry for itself because it didn't have any nematocysts and couldn't lash out to innocent human swimmers causing incredible pain to them. The jelly wanted to be the subject of a horror film, and wanted people to swim away in horror when they saw it. The jelly wanted to be respected.

The jelly propelled itself sideways, its oral lobe cast wide open to grab at a few plankton for lunch. It sidled up to the Wise Old Beroe and complained about the uselessness of its tentacles. "Fool," said the Beroe. "I have half a mind to gobble you right here and now. I don't even have tentacles, and you have the nerve to complain that you have no sting in yours? Why, if I had even the sticky tentacles that you do, I would be able to eat twice as many comb jellies as I already do."

Our little friend had forgotten all about the voracious diet of beroes, and that their preferred meal is in fact of the ctenophore phylum. It thought furiously, which is hard for a creature with no central nervous system, and came up with an idea. 'I'll make the Wise Old Beroe tell me a story about ctenophores getting one up on the humans. It'll be so busy telling me the story, it will forget that it wants to eat me.'

It was worth a shot, right?

"So, Wise Old Beroe, what was it that happened to the fisheries in the Black Sea?"

This was a subject that the Beroe loved to brag about, and as hungy as it was it couldn't resist telling the story.

"Around forty years ago, a group of adventurous Mnemiopsis leidyi stowed way in the ballast of a ship leaving port from the United States. The brave comb jellies dumped out in the Black Sea and found a plunder that they hadn't imagined possible. The beauty part was that since they were new to the black sea, there were no nasty predators to eat them. They had a high time, living off the sea, eating and multiplying until they took over the ecosystem.

"What had started out as a few meek gelatinous seafarers soon, by 1989, overwhelmed the anchovies. The Mnemiopsis starved out the other fish, growing to a mass of a billion tonnes. The humans were panicking. The comb jellies had scared the humans, but good."

"What happened next?" asked our little friend.

"What happens next is that I eat you," said the Beroe, which it promptly did. The Beroe was too hungry to tell the story, and it was boring to tell after a while.

But there is more:

Biologists considered introducing one of Mnemiopsis's predators such as Beroe ovata, another comb jelly to rebalance the food web. However the idea seemed too risky because attempts to use biocontrols, such as the introduction of the cane toad to Australia, can go horribly wrong. For example Beroe may also begin to eat native comb jellies or other species that are important to the ecosystem and therefore cause the original problems to escalate.

Then, without any intervention by humans, in 1997, B. ovata established itself in the Black Sea of its own accord, either by migrating naturally from the Mediterranean or possibly in ship's ballast water again. Initial occupation of coastal areas spread rapidly and by 1999 Beroe populations in the entire northeast region of the Black Sea.

"I could not believe it," says Tamara Shiganova of the Shirshov Institute of Oceanology in Moscow. Since Beroe arrived there has been a massive decline in the Mnemiopsis population while some species of plankton have begun to increase, Shiganova and her colleagues report in a paper that will appear in Hydrobiologia. Because B. ovata feeds upon animals similar to itself, such as Mnemiopsis, as opposed to the smaller zooplankton and fish populations, the initial reports look positive. However, the long term effects are much more difficult to predict. It will take many years of monitoring population cycles, ecosystem dynamics and seasonal variations in order to determine the true impact that this invasion will have.

Recently Casey Dunn of Brown University was quoted in a press release from his university as being shocked to find that a new study of which he was a chief author revealed a new twist in the emergence of ctenophores. The comb jellies he studied may have been the first multicellular animals in the ancient seas. The creationists jumped all over this because they thought it meant that since ctenophora are more complex than sponges, the "darwinist" story of emerging complexity had been disproven. Troy Britain at Playing Chess With Pigeons explains:

The article relates the surprise of the scientists who conducted the study, but doesn’t adequately explain that what was “shocking” was the difference between the expectations they had based on looking at the comparative morphologies of the living representatives from these two lineages and the results they got from their study which was looking at when (relatively speaking) the different lineages diverged genetically in the geologically distant past.

Living comb jellies are more complex than living sponges, but this genetically based study tells us nothing about what the ancestors of living comb jellies looked like when it originally split off the tree, or exactly how long ago this split occurred.

The creationist crowing was premature, and it was based on a press release. It was not based on a reading of the study.

So, I thought I would read a bit more about ctenophores, them being the source of some recent excitement, and I decided to share a few links that I found regarding comb jellies:

First, Claudia E. Mills lists the ctenophores here:

Mills, C.E. Internet 1998-present. Phylum Ctenophora: list of all valid species names. Electronic internet document available at Published by the author, web page established March 1998, last updated (see date at end of page).

As she requests on her page hosted by the University of Washington, I am not going to copy her work into this post. Just go there.

The Jellies Zone pages on ctenophores.

The strange bioluminescence of comb jellies.

I could go on for days with comb jellies, but I hope that this leads the reader to some great exploration of comb jellies. Remember to watch for the Beroes when you get to the Black Sea. The sad little jelly came to a bad end, and if you don't be careful, young'uns, the same end could befall you.


  1. Nice to see some ctenophore love. I didn't know that the creationists jumped on that phylogeny paper - that is highly entertaining.

  2. Nice post, Mike, and so fitting that Miriam commented since she also has a recent post about predator-prey interactions...

  3. I am glad you liked it, Karen. I went to Miriam's site following her comment, and it's a very good site. I have to add it to my feed reader and blog roll and

    I had mentioned the Dunn study to PZ on the radio yesterday, and he had kind of a chuckle over the creationist reaction to it.

  4. I guess I'm just in a food web state of mind. *sung to Georgia On My Mind* I'm flattered you liked my site, Mike!


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