The dramatic outbreaks of jellyfish in oceans around the world is largely driven by overfishing and climate change. Jacqueline Goy, of the Oceanographic Institute of Paris, told that jellyfish are an excellent bellwether for the environment. She said that the more jellyfish, the stronger the signal that something has changed. It is said that the brainless creatures composed almost entirely of water, the primitive animals have quietly filled a vacuum created by the voracious human appetite for fish.
According to marine biologists dislodging them will be difficult. Ricardo Aguilar, research director for Oceana, a international conservation organization, said that jellyfish have come to occupy the place of many other species. In Mediterranean basin the exploding numbers of jellyfish have devastated native marine species and threaten seaside tourism.
Centuries old data shows that jellyfish populations naturally swell every 12 years, remain stable four or six years, and then subside. Scientists believe that the over-exploitation of ocean resources by man has helped create a near-perfect environment in which these most primitive of ocean creatures can multiply unchecked. Jellyfish feed on small fish and zooplankton that get caught up in their dangling tentacles.
Andrew Brierley from the University of St Andrews in Scotland, explains that jellyfish both compete with fish for plankton food, and predate directly on fish. He further said that it is hard, therefore, to see a way back for fish once jellyfish have become established, even if commercial fishing is reduced.