At the first hint of the coming winter storms, Caribbean spiny lobsters form a long chain. As many as 50 lobsters may join together. They connect, conga-style, using their antennae to touch the backs of the lobsters ahead of them. It’s time for the lobsters’ annual journey, or migration.
Before hurricane season begins, these lobsters leave shallow waters to seek out deeper, less turbulent water. They go where the water is warmer and where the waves are less choppy. Here, the sandy bottom is still, and food is more plentiful.
To reach this place, they move single- mindedly and single-file like a silent army. They creep across the ocean floor for as many as 50 kilometers (31 miles). But what drives them?
We know that many animals migrate. They move from place to place, often at specific times or seasons. We even know why they migrate — to search for food or for places to breed. But we don’t always understand how they migrate. What are the mechanisms that trigger an animal’s urge to move?
Marine March
For these lobsters, the annual trek is brought on by shorter days in the fall and a sharp drop in water temperatures. The lobsters find their way by sight, using their knowledge of the underwater terrain. But they are also guided by Earth’s magnetic field.
Earth has a magnetic field that is undetectable to humans who aren’t holding a compass. Some animal species can detect it, however, and use it to direct their migrations.
Scientists aren’t exactly sure how this happens. One theory focuses on small particles of a magnetic mineral called magnetite that can be found in the brains of some species. Those particles may be reacting to Earth’s magnetic field. They may activate nerves to send information to the animal’s brain. Scientists think that this may help animals like the lobsters migrate.
antenna
Caribbean spiny lobsters link together when they migrate across the ocean floor.