Mediterranean Sea (Bernd F. Laeschke – September 2011): Jellywatch is a website that tracks the sighting of many different kinds of jellyfish, plankton blooms, and vertebrates around the world. Everybody can submit sightings via a phone app or through the website without creating an account. The site says that more than 2,000 sightings of jellyfish alone have been recorded in 2010. Jellyfish have always been a nuisance, but jelly blooms with massive swarms have become more frequent in recent years, especially in the Mediterranean Sea.
Jellyfish or Medusa are free-swimming members of the phylum Cnidaria. They have an umbrella shaped buddy and are found in every ocean at every depth. Some species are colorful and large, others can be found in bodies of fresh water. Scientists believe that jellyfish have been roaming the ocean for about 500 million years.
Jellyfish limited control over movement, but can use their hydrostatic skeleton to accomplish movement through contraction-pulsations. Their body is composed of more than 90 percent water. The rest is gelatinous material, or jelly. Instead of a brain or central nervous system, jellyfish have a loose network of nerves, which allows them to detect various stimuli including the touch. Contact with a jellyfish tentacle can trigger millions of venomous cells, also known as cnidocyte, cnidoblast, and nematocyte, to pierce the skin and inject venom, which can cause extreme pain or even death.
The population of jellyfish has swelled in recent years. In some areas like the Mediterranean Sea, the population has become a threat to tourism and other economic activities. Jellyfish can poison captured fish, and consuming fish eggs and young fish. They have also clogged cooling equipment and disabled power plants in several countries.
The largest known jellyfish is the lion's mane or Cyanea capillata. Its tentacles can be up to 120 feet (almost 37 meters) long. The lifespan varies from species to species and can range from a few hours to 30 years.