Jellyfishes

Jellyfish have been around for over 650 million years, long before the time of the dinosaurs. They are about 95% water and have a very simple nervous system, used for detecting light, orientation and salinity. They can actively hunt plankton and small pelagic fishes, using stinging cells on their tentacles called nematocysts. The prey is pulled into the body for digestion. Some fish have adapted to live among these tentacles without getting stung.

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Jellyfishes from Caribbean Reef Life on Vimeo.

The sting of some jellyfish can be quite painful to divers. Do not rub the area or apply fresh water, this will only cause more nematocysts to activate. Hot water or vinegar will neutralize some of the sting. The Thimble Jelly can gather in groups of millions of individuals. This is called a bloom, and usually occurs in late summer when nutrient levels in the ocean are high. The blooms can become so dense as to blot out the sun!

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