Jellyfish may lack brains, but these simple animals are far stronger at swimming than biologists once believed, according to a new analysis made from data collected by tagging several of the creatures.
The invertebrates are able to detect local currents and travel against them, the study found. This could help explain the formation of jellyfish "blooms," groupings of hundreds, thousands, or even millions of the primitive animals. Some of these blooms can stay together for months before dispersing.
Researchers tagged 18 large barrel jellyfish with electronic loggers, allowing investigators to carefully track the positions of the animals over the course of the study. A simple cable tie was used to harmlessly attach the devices to the animals. As the animals swam, researchers also record currents and other ocean conditions. What they found in the Bay of Biscay, off the coast of France, was unexpected.
"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. Jellyfish are not just bags of jelly drifting passively in the oceans. They are incredibly advanced in their orientation abilities," Graeme Hays of Swansea University in Wales and Deakin University in Australia said.
Researchers are baffled trying to determine how these simple animals are able to determine the direction of current and journey on a path against the water movement. One possibility is they move in response to ocean currents' shear forces acting on their bodies. Other ideas propose infrasound or detection of the Earth's magnetic field as means by which the creatures may navigate.
Jellyfish not only lack a brain, but they also lack a heart. These animals first evolved 500 million years ago, and jellyfish can currently be found in every ocean around the globe.
Directed swimming could help jellyfish blooms maintain cohesion, preventing individual animals from getting caught in currents, and potentially washed ashore.
Jellyfish swarms can be responsible for injuries to human swimmers who get stung by the animals, and the creatures can also clog fishing nets. However, jellyfish play a crucial role in the environment, serving as prey for leatherback sea turtles and other marine hunters. If the conclusions of this study apply to other varieties of jellyfish, the data may be utilized to better predict the formation, movement, and distribution of blooms.
Recent research has shown advanced behavior from brainless animals, including carnivorous plants.
Analysis of jellyfish behavior utilizing tracking devices was profiled in the journal Current Biology.
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