Homo jellyfishus

Humans are of course transforming the oceans in ways that we barely understand, but one vicar of change is the massive proliferation of jellyfish. Spiegel takes note in this story, which informs us:

Jellyfish are relatively simple organisms. Their bodies are about 98 percent water, with the remainder consisting of gelatinous tissue, sex organs, a gastrovascular cavity, a primitive nervous system and venom capsules which, when irritated, can eject venom projectiles with the momentum of bullets. There are roughly 1,500 known species of jellyfish, some as tiny as a grain of sand and others as heavy as a wildebeest.

Are they really “simple” and “primitive”? I think not. This is a gradistic or qualitative assessment, using talking primates as the standard by which all things are judged. Let’s consider the next segment of the story:

As fragile as the individual animals may seem, jellyfish are incredibly tenacious masterpieces of evolution. For about the last 600 million years, they have survived dramatic changes in the oceans — the development of fish, their biggest enemies and competitors for food, massive heat waves, ice ages, the emergence and disappearance of oceans and meteorite impacts — without changing significantly.

They are also more resistant to manmade environmental degradation than most other marine organisms. They are more capable of coping with pollution, algae blooms, murky water and oxygen depletion than fish. Overdeveloped shorelines and structures in the open ocean even serve as nurseries of a sort to jellyfish. The surfaces provide more habitat to the young animals, which attach themselves to fixed structures as polyps. Studies have shown that jellyfish infestations often occur in places where human beings use and pollute the sea with particular intensity.

Shipping also promotes the triumph of the jellyfish. When they are transported into new bodies of water in the ballast water of ships, they often settle successfully and displace local species. They are not picky eaters, consuming whatever enters their mouth opening. And if they can’t find sufficient food, they simply shrink their bodies temporarily.

What is more, jellyfish apparently benefit from climate change. Many species grow more quickly at higher temperatures. And tropical species like the sea wasp, whose venom can kill people within two minutes, are spreading in subtropical waters.

None of this sounds very “simple” or “primitive.” It’s no simple or primitive thing to eject venom projectiles with the momentum of bullets. In fact, jellyfish are exquisitely and complexly evolved. This aside, it is highly doubtful they have not undergone significant evolutionary change over the past 600 million years. Sparse (i.e., soft body impressions) fossil evidence showing a similar body-plan over time does not provide us with much information about other important traits, such as biochemistry and neurology, that surely have been evolving and continue to evolve. Jellyfish are a highly diverse group and it seems a safe bet there has been a great deal of speciation over the past 600 million years. And given changing conditions in the oceans, this speciation may well be accelerating.

While humans like to think that our evolutionary success is due to plasticity and adaptability, jellyfish are right there with us and may ultimately have the last laugh. If only those primitive creatures could laugh like complex sponges.


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6 thoughts on “Homo jellyfishus

  1. Sabio Lantz

    Fantastic post, Cris. The common misunderstandings of evolution abound. And part of the reason is the preference to see humans as the pinnacle of all that is.

    But question: why do they think jelly fish are flourishing while other organisms are dying?

  2. Cris Post author

    I’m glad you enjoyed it Sabio; I enjoyed thinking about it and writing. As for your question, I can only make some educated guesses; I have never read anything about jellyfish and this seems to be a shortcoming that needs to be remedied.

    The big question here is whether all ~1500 species of jellyfish are flourishing rather than just specific genera or species. If only some taxa are flourishing, then there is probably something specific about them which is driving it.

    But having said that, I’m guessing that jellyfish success has something to do with plasticity; specifically, they appear to be able to thrive in a wide range of chemical conditions. There aren’t many organisms capable of doing this, so it’s a big deal. In other words, their adaptive “sweet spot” is probably more like a huge zone.

    Ironically, they may do better under conditions that we, from an anthropocentric perspective, consider to be less than ideal or off-kilter. We would probably call oceans filled with jellyfish but not lots of other metazoa “dead.” This would of course be far from the case.

    Jellyfish have obviously crossed over some major extinction boundaries, such as the Permian, without difficulty. They may also be able to speciate at relatively rapid rates (they are, after all, sexual reproducers), which is always a good thing under changing environmental conditions.

    It’s hard to argue with 600 million years of evolutionary success. It may be the case that jellyfish, rats, and cockroaches inherit the earth.

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