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Jellyfish Sense Their Environment for Controlled Migration


Jellyfish are not exactly the quarterbacks (or leatherbacks) of the animal kingdom, but they have surprised researchers with their ability to swim against the tide, just like baby leatherback turtles do. Scientists even think they may be able to sense the earth’s magnetic field, as do turtles, salmon, birds, and other long-distance migrators. The BBC News comments on new findings from Australia:

The scientists think the animals might sense the current across the surface of their bodies. They also speculate that the jellyfish might use the Earth’s magnetic field to navigate — an ability seen in some other migrating marine species, including sea turtles. (Emphasis added.)

Regarding sea turtle navigation, see our report here.

We noted in 2013 that jellyfish, which appear suddenly in the fossil record along with all the other animal phyla in the Cambrian explosion, are much more complex than the simple drifters they appear to be. They contain a nervous system, muscles, and sex organs. Their integrated systems allow them to win a world championship, too: last year, The Conversation called them the most efficient swimmers in the animal kingdom — a remarkable achievement in a field of contenders like tuna, dolphins and Michael Phelps. Watch them swim in real time here. Not exactly a Sea World show, but impressive for its efficiency and grace.

The new findings were published in Current Biology this month. For the first time, researchers put data loggers on jellyfish to track their movements. How does one put a data logger on a soft jellyfish? Very carefully. They have stinging cells, after all, that are marvels of engineering — tiny harpoons with hair-trigger action that stun their prey, as many a human swimmer has found out painfully. (How leatherback turtles can eat jellyfish without suffering the consequences is another mystery. Then there are sea slugs that can eat the stinging cells, swallow them unexploded, and put them on their backs for protection.)

Anyway, the researchers found a way to cinch the loggers to their "necks" (peduncles) with cable ties, and then recorded their movements. To the scientists’ surprise, the jellyfish swam against the current — proving that they use active sensing to detect the ocean current and swim across it, when necessary, to get where they want to go. PhysOrg quotes one of the authors in astonishment:

"Detecting ocean currents without fixed visual reference points is thought to be close to impossible and is not seen, for example, in lots of migrating vertebrates including birds and turtles," says Graeme Hays of Deakin University in Australia.

"Jellyfish are not just bags of jelly drifting passively in the oceans," he adds. "They are incredibly advanced in their orientation abilities."

Where are the sensors located? How do they work? "It remains unclear just how the jellyfish sense changes in water, the paper in Current Biology journal says" (BBC News). It must work really well, because jellyfish get together in big convocations called blooms. "These blooms may comprise between hundreds and millions of jellyfish, and can persist in a given area for months."

There are mysteries here that will require further research to understand. The authors speculate about what environmental cues these soft-bodied living submarines might employ for navigation:

Several other mechanisms could help jellyfish indirectly assess their drift and current direction. They may detect the orbital motion of waves, which can be linked with the direction of water flow at the surface layer, as previously described in hatchling turtles… Relative changes in the magnetic field could also provide jellyfish with an indication of their drift direction as described in other species… Whether jellyfish can detect such changes over half a tidal cycle and a horizontal displacement of a few kilometers remains to be tested. Jellyfish may also use infrasounds to orientate themselves, as shown in birds and several marine species… The statocysts, organs located at the margin of the jellyfish’s bell, enable jellyfish to detect gravity, sense vibrations, and potentially sense pressure variations, and may therefore contribute to the ability of jellyfish to directly or indirectly detect current flow.

Other families of jellyfish, the scyphozoans and cubozoans, have photoreceptor organs that add sunlight as a navigational cue. The ones tested here lack photoreceptors, but succeeded in migrating anyway. If jellyfish use a combination of cues, they must have a way of integrating the information to effect goal-seeking behavior.

This finding opens up new questions about other "slow-moving" animals.

The fact that free-living jellyfish can actively change their swimming direction in response to current drift and changing current flows poses questions of how widespread this ability is among other slow-moving taxa and what the adaptive significance of this strategy might be for each taxon. Such questions are essential for understanding the evolution of animal orientation strategies.

Meanwhile researchers continue to observe design in the living world, then believe that their job is to find out how it fits a Darwinian scheme. "It’s there; it’s adaptive; it must have evolved!" is the mentality. But a strategy implies direction and purpose. We know that in every case where we observe the origin of a strategy, intelligence — not blind nature — was the cause.

Dr. Timothy Standish, who appears in Flight: The Genius of Birds, gave this response to the new findings.

The thing that has me most amazed about this is how jellyfish detect currents. All the paper and comments on it do is speculate, and that is all we can do at the moment as we really don’t know. Detecting your own movement in an ocean current is a tremendous problem to solve without a clear frame of reference and the senses to detect it. Clearly jellyfish, with their "simple" nervous systems, are detecting things that we humans seem to lack the capacity to detect. In addition, they are integrating the information they are getting from no-one-knows-where into a coordinated and consistent response.

So a "simple" animal performs a complex function that humans cannot do without instruments. Is it the scientist’s job to "understand the evolution" of such a function?

A design approach, that observes an animal solving a problem and tries to understand how it does so, is much more satisfying than saying, "It evolved." It may even lead engineers to mimic the animal’s design to solve human problems. Intelligent design also keeps the fascination and wonder in science. It leads to a view of nature as a world of intricate designs that are a delight to contemplate and try to figure out.

By Paroxysm [CC BY-SA 2.0], via Wikimedia Commons

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