Jellyfish: The New Sharks
Jellyfish have become the top predators in parts of the ocean where large fish species have declined because of human activities, according to a new report by an international team of scientists. Such human activities as “fishing, pollution, aquaculture, global warming, and coastal development can all create conditions which favor jellyfish over fish,” commented Lucas Brotz of the University of British Columbia, one of the researchers.
The study revealed that although jellyfish mostly float rather than swim, they can capture prey as well as such large marine predators as sharks and tuna. Jellies “hunt” by creating water currents that carry prey to their oral arms and tentacles. The researchers reported that hunting ability depends partly on how fast predators can catch and eat their prey. But they found that jellyfish are more efficient than large fish in using that food to grow and reproduce. In part, the floating jellies do not need to eat as much as large predator fish, which must swim over a wider area to catch enough food.
The scientists also reported that jellyfish are actually getting larger. Jellies grow by increasing the amount of water in the jellylike material that serves as a skeleton. The larger a jellyfish is, the more likely it is to encounter prey.
The scientists warned that if the numbers of large predator fish continue to drop, the oceans could become as “gelatinous” as they were 600 million years ago during the Ediacaran Period. At this time, Earth’s oceans were filled with simple, soft-bodied creatures. Such conditions could increasingly threaten a wide range of human activities. Currently, jellies sometimes clog the water intake systems of nuclear power and desalination plants located along coastlines.
Additional World Book articles:
- Cnidarian
- Portuguese-man-of-war
- Invasion of the Jellyfish (special report)
- The Secret Lives of Jellyfish (special report)