The word jellyfish is a common term used to describe animals that are gelatinous or made up of ‘jelly-like’ material. There are many different types of jellyfish, including stinging kinds called medusae and non-stinging kinds called comb jellies or ctenophores.
What is a bloom?
When huge numbers of plants or animals appear suddenly, scientists call it a 'bloom'. In some areas of the world, millions of jellyfish can swarm together, and these blooms cause problems for fisheries and tourism. If you've been at the beach or on a boat at some point when it seemed like jellyfish were everywhere – then maybe you have even seen a jellyfish bloom.
How long do jellyfish live?
Most jellyfish live less than one year, and some some of the smallest may live only a few days. Each species has a natural life cycle in which the jellyfish form is only part of the life cycle (see video clip showing different life cycle stages). The most familiar stage is the medusa stage, where the jelly usually swims around and has tentacles hanging down. Some scientists believe that jellyfish have increased because coastal development helps provide more underwater habitat for jellyfish polyps to grow.
What do they eat?
Jellyfish eat many different types of things, such as small plants (phytoplankton), copepods (crustacean zooplankton), fish eggs and other small fish called larvae; they also eat the planktonic eggs and young stages (also called larvae) of many different kinds of marine animals.
Are there good things about jellyfish?
Yes, jellyfish are very important animals in the ocean. They are food for a number of marine animals such as large fish and turtles. Even humans eat jellyfish. Jellyfish also provide habitat for many fishes in areas where there are not many places to hide. They can also protect the small fish from being eaten by predators with their stinging cells.