What are Jellyfish?

Chrysaora fuscescens

Jellyfish are actually not fish as the name suggests, but members of the invertabrate phyllum called, Cnidaria. Found exclusively in the water, this species is distinguished by its cells called cnidocytes, which are specialized venomous cells meant for capturing prey. This is what gives the jellyfish its sting! These are the cells that are found on their tentacles and are the only place where their venom is found. The other parts of the jellyfish are harmless.

How do Jellyfish survive?

The jellyfish's body is composed of an inert jelly-like substance called Mesoglea. Jellies, as they are also called by scientist, are made of 96% water and tend to collapse on land. Their bodies are structured in a way that they eat through the anus. Their diet consists of mainly plankton, fish eggs and small crustaceans. They've even been know to eat other Jellyfish as well. The tentacles carry the food to the stomach like pouch where the nutrients are absorbed by the gastrodermal lining contained within the gastrovascular cavity.
Jellyfish breathe through a process called diffusion in which their motion causes their body to be oxygenated. Although they have limited control of their movement, they move through contraction-pulsations of their bell-like body. Some species of jellyfish "swim" while others just float passively. The motion of the ocean can help them breathe and they are also able to tolerate low oxygen levels.

Are Jellyfish a problem?

Jellyfish have been around for millions of years and thrive in warm waters. Human impact on the environment has actually benifitted the Jellyfish. The warmer waters and lower oxygen that has become an increasing threat to many species of fish are conditions that the jellyfish can tolerate. Swarms of Jellyfish, called "blooms" are increasingly becoming problems for both marine life and humans. Their sting can be toxic and sometimes even fatal. The proliferation of these blooms have overtaken fish habitats and caused many beaches to be closed when the blooms overrun the swimming areas. Their proliferation has also impacted the fishing industry by destroying fishing nets, killing the harvest, and feeding on fish eggs.Increased awareness of the impact that humans have on the oceans can be studied by observing Jellyfish from all over the world.

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