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Jellyfish Gone Wild — Text-only | Flash Special Report
Gulf of Mexico

THE BIGGEST DEAD ZONE IN THE WESTERN HEMISPHERE

The white sands and sparkling emerald waters of the Gulf of Mexico’s beaches belie a dirty little (open) secret: a huge Dead Zone that is devoid of almost all life except jellyfish is expanding in the Gulf of Mexico. During the summer of 2008, the Gulf’s Dead Zone covered about 8,000 square miles, about the size of Massachusetts. It is expected to soon reach about 10,000 square miles.

CREATION OF THE DEAD ZONE
The Gulf’s Dead Zone is produced every summer by tons of fertilizer, sewage and animal wastes that are continuously dumped into coastal waters by the Mississippi and Atchafalaya Rivers. These pollutants do their dirty work by fertilizing huge algae blooms that decay through a process that robs Gulf waters of oxygen. Most sea creatures flee or suffocate to death in the Dead Zone’s oxygen-starved waters, leaving highly adaptable jellyfish to proliferate unrestrained by predators and competitors and to gorge on the Gulf’s bounty of plankton.

GROWING JELLYFISH POPULATIONS
The most abundant species of jellyfish in the Gulf are the sea nettle and moon jellyfish, which typically swarm over hundreds and perhaps even thousands of square miles each summer. Studies show that these species became significantly more abundant and expanded their ranges during the 1980s and 1990s. Moreover, since 2000, the Gulf has hosted invasions of several non-native jellyfish species, including the Australian jellyfish.

Signs that the Australian jellyfish is satisfied with its adopted Gulf home include its tendency to swell from its usual fist-size to the size of dinner plates in the Gulf. In addition, the Gulf’s population of Australian jellyfish is steadily growing and expanding its range; this species recently reached North Carolina.

OTHER JELLYFISH-FRIENDLY FACTORS
Other factors besides the Dead Zone that probably encourage Gulf jellyfish to proliferate include:

  • The creation in the Gulf of artificial habitat for young jellyfish (called polyps) that cling to hard surfaces by the presence of about 6,000 oil and gas production platforms and artificial reefs that are designed to support fishing. These artificial reefs are composed of at least one discarded bridge and acres of shopping carts, vehicles and other junk.

  • The over-harvesting of fish that compete with jellyfish for food.

  • The importation of invasive species of jellyfish into the Gulf by currents from the Caribbean and ships that provide hard surfaces to which young jellyfish cling.

GLOOM FROM BLOOMS
The Gulf’s growing Dead Zone intermittently shuts down the Gulf’s important shrimp industry: shrimpers do not even dare venture into the Gulf for dozens of days during typical swarm seasons because jellyfish masses would break their nets and clog their engines beyond repair.

Just the invasion of the Australian jellyfish alone cost the shrimp industry about $10 million dollars in 2000--not even counting the indirect costs of the consumption of eggs and larvae of commercial fish by these invading jellyfish.

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Caption/Credit:

THE DEAD ZONE
Reds and oranges mark the Dead Zone in the Gulf of Mexico. The Gulf’s Dead Zone covered about 8,000 square miles in 2008.

THE THIN LINE BETWEEN LIFE AND DEATH
Turbid Mississippi River water enters the Gulf of Mexico, dumping sediment, plants, fertilizer and other pollutants that promote the expansion of the Gulf of Mexico’s Dead Zone, which is hospitable to jellyfish but few other animals. Credit: Nancy N. Rabalais