Jellyfish Gone Wild — Text-only | Flash Special Report
Ecology

ECOLOGICAL ROLES OF JELLYFISH

Plying the world’s oceans for over 500 million years, gelatinous creatures have influenced marine communities almost as long as marine communities have existed.

As prey, gelatinous creatures are eaten by seabirds, pink salmon, sun fish, turtles and other gelatinous creatures.  (Animals that eat jellyfish are not impacted by their stings.)  As predators, gelatinous creatures eat fish eggs and larvae, invertebrates, small, floating creatures called zooplankton and other gelatinous creatures.

Scientists are continuing to identify new ecological services provided by jellyfish.  For example, recent studies show that the tentacles dangling from the Bering Sea’s large jellyfish provide hiding places for young pollock that are pursued by other predators but have grown too big for the jellyfish to eat.

IMPACTS OF RUNAWAY POPULATIONS

When populations of gelatinous animals explode, various types of ecological changes may result.  For example:

• During the 1990s, a voracious, invasive jellyfish-like creature known as the comb jelly was introduced into the Black, Azov and Caspian Seas.  Uncontrolled by natural predators, comb jelly populations quickly ran wild.  The rise of the comb jelly contributed to crashes in the populations of anchovies in the Black and Azov seas and to crashes of a small commercial fish known as kilka in the Caspian Sea.

How did the comb jelly damage the populations of these commercial fish?  By eating their eggs and larvae and by eating the same zooplankton prey they eat.  The resulting reductions of anchovy and kilka catches in the Black, Azov and Caspian Seas have cost area fishermen hundreds of millions of dollars. 

The impacts of the rise of the comb jelly in the Black, Azov and Caspian Seas have cascaded up the food chain.  For example, seals of the Caspian Sea have suffered from the virtual decimation of populations of their kilka prey by comb jellies.

Increases in comb jellies can help cause massive algae blooms. Here's why: when populations of comb jellies increase, populations of their zooplankton prey decrease. The result: controls on algae populations that are otherwise provided by zooplankton are reduced or eliminated. Lacking controls, algae populations may explode.

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Caption/Credit:

FEWER TURTLES; MORE JELLYFISH
All seven species of sea turtles eat jellyfish and all seven species are endangered. Their survival is threatened by fishing lines that trap them, pollution, beach development, climate change and sales of turtles and turtle parts. Credit: Mito Paz

IN THE BELLY OF A JELLY
A fish was recently captured by this freshly caught box jellyfish Carybdea alata in Honolulu, Hawaii. Credit: Dr. Angel Yanagihara, PBRC, University of Hawaii