Science Scoops: Lobsters Know the Way

Only a few species of animals are known to have “true navigation” — meaning that they can find their way home even if transported to a totally different and unfamiliar environment. Most vertebrates are thought to be true navigators, but vertebrates make up only about one percent of all known living species. To date, only one species of “spineless” wonders (invertebrates) have been shown to be capable of true navigation, the Caribbean spiny lobster, Panulirus argus.

For most of the year, spiny lobsters spend daylight hours inside coral reef crevices, emerging at night to feed over considerable areas before returning in nearly total darkness to the same den. Spiny lobsters also show a remarkable ability to keep a constant course while migrating under water and to find their way even in darkness. Now researchers have discovered that they can also return to their feeding grounds after being displaced by some 12 to 37 kilometers.

How do the lobsters navigate so well?

To test a theory that spiny lobsters have a well-developed magnetic map sense, Larry Boles and Kenneth Lohmann (Department of Biology, University of North Carolina, Chapel Hill) captured lobsters, which they then relocated — some to the north of the capture site and some to the south.

The result?

The lobsters relocated north of the capture site immediately oriented themselves southward, whereas those relocated south of the capture site oriented themselves northward. When instead of transporting the lobsters, the investigators simulated the values of the magnetic field that would be encountered at northern and southern sites, the lobsters showed the same responses. So true navigation in spiny lobsters, and perhaps in other animals, is based on a remarkable “magnetic map sense” similar to that found in newts and thought to play a role in the long-distance movements of other vertebrates such as sea turtles and migratory birds.

Vocabulary

  • invertebrate: An animal that has no backbone. Worms, clams, insects, and lobsters are invertebrates.
  • magnetic map sense: The use of the Earth's magnetic field as a way to know a position and navigate to a new position.
  • simulated: Imitated.
  • vertebrate: Any of a large group of animals that have a backbone. Fish, amphibians, reptiles, birds, and mammals are vertebrates.

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Activity

  1. Is the magnetic map sense demonstrated by lobsters a response to internal or external stimuli?
    [anno: external]
  2. Millions of animals migrate through the ocean every year. If a lobster were born without this magnetic map sense, what problems might this cause for the lobster? Write a few sentences explaining what kinds of problems this might cause.
    [anno: Answers will vary but could include the lobster not being able to find its way back to certain food sources, the lobster not being able to find other lobsters for mating, or the lobster not being able to find its way back to the protection of the reef during the day.]