Printer Friendly

Attack of the jellyfish: recently, swarms of jellyfish have been growing larger--causing humans grief. Are people to blame for their surge?


What would it take to temporarily halt operation of the largest power company in California? Jellyfish. Last October, pipes that pull in water from the ocean to cool two nuclear reactors run by PG&E Corp also sucked in enormous numbers of jellies. The gobs of gelatinous animals clogged the intake pipes, forcing the company to shut down one of its reactors and put the other on 50 percent power.

This incident is just one of many recent reports of hordes of jellyfish in the world's oceans. Half a world away, jellyfish are hampering fishermen and sidelining surfers (see map, p. 20). That has scientists wondering what's to blame for the rise in jellyfish swarms.


Jellyfish look like aliens, with slimy bubble-bodies made from translucent goo complete with dozens of squiggly hanging tentacles. Jellies are composed of 95 percent water (humans are 65 percent water). The rest of their body is made up of proteins and minerals that form cells, organs, and a flexible skeleton made of collagen--the same material that allows the human ear and nose to bend.


Although jellyfish have the word "fish" in their name, they are not fish at all. They are invertebrates, meaning that their bodies have no bones. Part of the phylum Cnidaria (nigh-DARE-ee), jellyfish are very simple creatures. They don't have gills, a heart, blood, or even a brain. They have a bell-shaped body and usually tentacles that contain stinger-cells called cnidae (NIGH-day), which secrete poison that protects against predators, but also helps them to stun small fish and shrimp. Even a dead jellyfish that washes up on the beach still has functioning stingers.


Recently, troublesome masses of jellyfish called jellyfish blooms have been popping up. These clusters of slimy creatures can get so big that they can cover thousands of square miles. Giant swarms of jellyfish are invading areas where they have never been found before, and certain species of jellies are invading locations far away from their native habitat.

During the summer of 2007, at the beaches of Hawaii's Oahu Island, swimmers were forced from the ocean due to giant swarms of box jellyfish. A type of box jellyfish, called Chironex fleckeri, is found in waters off northern Australia. It is the most poisonous animal on Earth. The stingers contain the most potent and deadly venom of any animal--so strong it could kill a person within three minutes. It wasn't until recently that box jellies could be found in Hawaii. They are common to waters in Australia, and in the Philippines alone they kill 20 to 40 people annually.

Fishermen aren't off the hook either: Swarms of jellyfish have begun to damage their fishing nets, clog their boat engines, and even poison and squish the fish they catch. Jellies also eat fish eggs and young fish, harming future generations of fish.


Scientists think humans might be playing a role in jellyfish blooms. "There is mixed evidence of an increase in blooms. In some cases, human behavior seems likely to be causing [blooms] to be larger and form in unusual locations," says Michael Dawson, a marine biologist and jellyfish expert at the University of California, Merced. "Humans might be increasing [jellyfish's] food supply and reproduction, decreasing the animals that prey on jellies, or making other changes leading to more jellies," he says.

Experts say that agricultural runoff, or water that contains fertilizers to help crops grow, makes its way into coastal waters. These same chemicals that help land plants grow also cause algae in the ocean to grow and flourish. "Algae is a big food source for the food that jellyfish feed on, called microzooplankton," says Dawson. When jellyfish stay well fed, they live longer and, therefore, reproduce for a longer period of time. One jellyfish can release 45,000 eggs a day, so their numbers can quickly skyrocket.

Shipping practices, extreme pollution, and over-fishing are also among the likely causes of recent jellyfish blooms (see Nuts & Bolts, right). According to Dawson, climate change, which is causing ocean temperatures to rise, isn't helping matters either. "We aren't sure why, but warmer water makes jellyfish reproduce significantly faster," he says.

Given that humans are a cause of the slimy swarms, is there anything people can do to curb the jellyfish blooms? "People have to be more conscious about the actions they take that might negatively influence nature, whether it be farming, fishing, or shipping habits," says Dawson.


* What do jellyfish look like? What are they made off

* What industries might be harmed by an increase in jellyfish?

* What might be causing an increase in the number of jellyfish?


* The largest jellyfish ever discovered, a lion's mane jellyfish, weighed more than 200 kilograms (450 pounds)

and had tentacles extending more than 35 meters (115 feet). However, don't expect to see one--most lion's mane jellies live in Arctic waters.

* While most jellyfish do not have organs, box jellies have an extremely advanced eye--containing all of the structures of the human eye, such as a retina, lens, and iris. Still, experts do not know if the box jellies can perceive objects, since the animal does not have a brain to process information coming from its eye.

* Just as a group of birds is called a flock, a group of jellyfish is called a "smack."


* Look at the environmental stresses described in the table "Environmental Changes Trigger Jelly Blooms" (see p. 21). What do you think can be done to keep jellyfish from taking over the oceans?


LANGUAGE ARTS: Use your knowledge of jellyfish to create a tall tale in which you are a sailor hero and jellyfish play an important role in the story. Review the tall-tale checklist at: /2267_talltales_checklist.pdf. Then, write your story on a separate sheet of paper and share it with the rest of the class.


* Learn how to identify different types of jellyfish and see what else the Dauphin Island Sea Lab in Alabama is doing to monitor jellyfish blooms at their Dock Watch Web site:

* Ouch! What to do when stung by a jellyfish: /watersafe/jellyfish.htm.

* Find out more about invasive species here: /wgbh/nova/algae/. And be sure to check out the accompanying video Deep Sea Invasion that documents the spread of nasty algae throughout the oceans.


DIRECTIONS: The phrases below describe events commonly associated with jelly blooms caused by agricultural runoff. Read each phrase, and then place the letters of the phrases below in the order in which they would occur from first to last.

a. The chemicals in fertilizer runoff cause algae in the ocean to grow and flourish.

b. The number of jellyfish eggs produced increases and jellyfish numbers skyrocket.

c. An abundant food supply allows jellyfish to stay alive longer and reproduce for a longer period of time.

d. A farmer fertilizes his crops.

e. Giant swarms of jellyfish invade areas where they have never been found before.

f. Jellyfish "blooms" start to appear.

g. Water containing excess fertilizer enters coastal waters.

First --, --, --. --, --, --, --, Last


d, g, a, c, b, f, e


All Aboard!

You read in "Attack of the Jellyfish" (p. 18) that cargo ships unintentionally transport critters around the world in their ballast. Sometimes these invasive species can take root and harm their new ecosystem. Researchers in Oregon studied ballast water in order to find out how many creatures hitched a ride. Complete this activity to learn more.
Organisms Found in Ship Ballast

Phylum                                  Number of organisms

Annelids (segmented worms, leeches)              43
Cnidarians (jellyfish, hydra)                    25
Diatoms (green algae)                           128
Crustaceans (lobsters, shrimp, krill)            72
Fish (cod, catfish)                               2
Mollusks (squid, mussels)                        19



Graph it

On graph paper, create a bar graph comparing the number of organisms from each phylum that were found in the ship ballast. Give your graph a title and don't forget to label the x- and y-axes.

Analyze it

1. Which type of organism was found in greatest abundance in the ballast?

2. What is the total number of species transported in the ballast?

3. Were there more cnidarians or crustaceans in the ballast? How many more?

4. Why do you think so few fish were found in the ballast?


COPYRIGHT 2009 Scholastic, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2009 Gale, Cengage Learning. All rights reserved.

Article Details
Printer friendly Cite/link Email Feedback
Title Annotation:EARTH OCEANS
Author:Klein, Andrew
Publication:Science World
Geographic Code:1USA
Date:Feb 2, 2009
Previous Article:The name game: scientists have a sense of humor--especially when it comes to naming new species.
Next Article:Environmental changes trigger jelly blooms.

Terms of use | Privacy policy | Copyright © 2018 Farlex, Inc. | Feedback | For webmasters