Skip all navigation and go to page contentSkip top navigation and go to directorate navigationSkip top navigation and go to page navigation
National Science Foundation
Special Report
Text-only
design element
Jellyfish Gone Wild — Home
Introduction
Biology
Ecology
Swarms
Sea Stings Back
Bloomin' Magic
Chart - Environmental Stress
Video
1
Locations
1
Gallery
1
Resources
1


Jellyfish Gone Wild — Text-only | Flash Special Report
Swarms Chart

STRESSED OUT SEAS:
ENVIRONMENTAL STRESSES THAT MAY PROMOTE JELLYFISH SWARMS

Jellyfish represent an ecological “perfect storm” -- able to prosper from various types of environmental stresses that are currently proliferating in many parts of the world.

---------------------------------------------------------

TYPE OF ENVIRONMENTAL STRESS
Invasions of non-native jellyfish

HOW ENVIRONMENTAL STRESS MAY INCREASE JELLYFISH POPULATIONS
Ships transport jellyfish around the world in two ways:

1. Juvenile jellyfish (called polyps) cling to ship hulls and therefore travel with ships.

2. Ships take on ballast water, needed for stability, in originating harbors. In destination harbors, ships may dump their ballast water along with  accompanying organisms, including jellyfish.  (Billions of gallons of ballast water are transported around the world annually.)

Jellyfish that are released into non-native habitats may colonize them--particularly if they face few or no predators in these habitats.

Underscoring the importance of shipping to global jellyfish movements is a recent study of moon jellyfish, which currently live in many worldwide locations.  Conducted by Michael Dawson of the University of California at Merced and others, the study incorporates computer simulations of the global distributions of populations of moon jellyfish over the last 7,000 years, based on ocean currents and other factors.

Results show that “it is very unlikely that the current global distribution of moon jellyfish is natural,” says Dawson.  “Shipping is the most viable mechanism responsible for the current global distribution of jellyfish.”

EXAMPLE LOCATIONS
Black Sea
Gulf of Mexico
Hawaii

---------------------------------------------------------

TYPE OF ENVIRONMENTAL STRESS
Pollution

HOW ENVIRONMENTAL STRESS MAY INCREASE JELLYFISH POPULATIONS
Jellyfish are among the only creatures that can adapt to utra-polluted, oxygen starved waters known as Dead Zones.  Lacking competitors and predators in Dead Zones, jellyfish tend to thrive in such waters.

From 2004 to 2006 alone, the number of global Dead Zones--which each coverto 45,000 square miles--increased from 150 to 200.

EXAMPLE LOCATIONS
Gulf of Mexico
Chesapeake Bay

---------------------------------------------------------

TYPE OF ENVIRONMENTAL STRESS
Climate Change

HOW ENVIRONMENTAL STRESS MAY INCREASE JELLYFISH POPULATIONS
Increasing water temperatures may expand the geographic and seasonal ranges of jellyfish.

When droughts reduce river flows into coastal waters, coastal waters become saltier.  Under such conditions, coastal waters may provide habitat to jellyfish that usually avoid coastal waters in favor of saltier waters.

EXAMPLE LOCATIONS
Narragansett Bay
Bering Sea
Australia

---------------------------------------------------------

TYPE OF ENVIRONMENTAL STRESS
Over-harvesting of fish

HOW ENVIRONMENTAL STRESS MAY INCREASE JELLYFISH POPULATIONS
The over-harvesting of fish removes jellyfish predators and fish that eat the same food as jellyfish. Fewer predators and more food for jellyfish means more jellyfish.

EXAMPLE LOCATIONS
Black Sea
Namibia

---------------------------------------------------------

TYPE OF ENVIRONMENTAL STRESS
Dams

HOW ENVIRONMENTAL STRESS MAY INCREASE JELLYFISH POPULATIONS
By reducing the flow of fresh water and nutrients into coastal waters, dams may--together with other environmental stresses and under some circumstances-promote conditions favoring jellyfish.

Scientists suspect that swarms of giant jellyfish that drift into the Sea of Japan originate in China’s coastal waters, which have been impacted by the gigantic Three Gorges Dam and many other environmental stresses.

Dams on the Danube River may have been one of many factors that set the stage for population explosions of comb jellies in the Black Sea.

EXAMPLE LOCATIONS
China
Black Sea