Before dinosaurs roamed the earth, there were creatures that drifted along the ocean currents called jellyfish. They have existed for millions of years and are large populations of jellyfish live in cold and warm ocean water, in deep water, and along coastlines. Even though the word fish is in their name, they are not fish but invertebrates, which are animals without backbones. There are many different types of jellyfish, including stinging kinds called medusae and non-stinging kinds called comb jellies or ctenophores.
Jellyfish are known for their stings to thousands of swimmers every year. They have tiny stinging cells in their tentacles that are used to stun or paralyze their prey before they eat them. They eat and discard waste from the same opening inside their bell-shaped body. As a jellyfish squirts water from its mouth, it is propelled forward, and their tentacles hang down from a smooth baglike body used to sting their prey.
The stings may be harmful to human and sometimes dangerous, but the jellyfish do not purposely attack people. Instead, people accidentally touch the jellyfish and get stung by the tentacles. If a sting is from a dangerous species, it can be deadly for the person. A jellyfish digests its food very quickly which helps them easily float without needing to carry around undigested food.
A jellyfish's diet includes small fish called larvae, fish eggs, shrimp, crabs, other jellyfish, and tiny plants called phytoplankton, and jellyfish may be eaten by sea turtles. Many of the jellyfish along the coastline are clear, but others come in very bright colors like pink, blue, yellow, and purple and are often luminescent. Jellyfish are used as a medicine and a delicacy by the Chinese for over 1,700 years.
In some parts of the world when millions of jellyfish swarm together, it is called a bloom. The blooms cause problems for fisheries and tourism. Blooms often form when two currents meet, and thousands of jellyfish are beached. When jellyfish form blooms they eat almost everything in the water and this can cause problems for fisheries because there is no food left for the fish to eat. For tourists, the jellyfish blooms may lead to closed beaches
Most jellyfish species live for less than one year, and some of the smallest ones live for only a few days. They can range in size from about 1 millimeter or 0.03 inches to nearly 6.6 feet. Each species has a natural life cycle in which the jellyfish form is only part of the life cycle. The most common stage is the medusa stage when the jelly usually swims around and has tentacles hanging down. Male and female medusae reproduce and form thousands of very small larvae called planulae.
The larvae then settle on the bottom of the ocean on rocks and oyster shells and form a small polyp that looks just like a tiny sea anemone. Each polyp will bud off many baby jellyfish called ephyrae that grow very quickly into adult medusae. Coastal development helps provide more underwater habitat for jellyfish polyps to grow which may be the reason for an increase in the jellyfish population.
Though jellyfish can often be a nuisance, they are important animals in the ocean. They are part of the diet for many marine animals such as large fish and turtles. The jellyfish also provide a habitat for many juvenile fishes in areas where there are not many places to hide. Many young crabs may sit atop jellyfish, so they do not have to swim.
There are about 200 known species of jellyfish that inhabit the oceans or about 1,500 types which include Lion's mane jellyfish, black jellyfish, purple-striped jelly, egg-yolk jellyfish, cannonball jellyfish, moon jellyfish, and many others. The most common species in the world can be identified by the four horseshoe-shaped gonads that can be seen through the top of the bell and range in size from 6 to 20 inches.
To link to this Jellyfish page, copy the following code to your site: