University of Miami Rosenstiel School of Marine and Atmospheric Science
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Moon Jellyfish


Jellyfish are a free-swimming marine invertebrate belonging to the scientific phylum Cnidaria. The term 0485comes from the Greek word for “sea nettle.” Species that share this phylum include corals, sea anemones, and hydroids. All Cnidarians contain stinging cells known as cnidocytes, which fire a structure known as a nematocyst. This nematocyst contains a toxin that is used to stun in self-defense, or in an effort to capture prey. Jellyfish usually prey on plankton, small larvae, fish eggs, and sometimes small fish and other jellyfish if they are large enough to consume them. Their tentacles act as a net to catch their prey. They are opportunistic but passive feeders who rely mostly on the currents or minor jet propulsion to move from place to place.
Jellyfish are an interesting species that vary in degrees of harm they pose to humans. Some jellyfish, such as Moon Jellyfish, will only leave a slight itching sensation when a human comes into contact with its stingers. In other cases, a jellyfish tentacle wrapping around a person’s leg will leave more of a burn and possible scaring. The Box Jellyfish, sometimes referred to as the Sea Wasp, is notorious for causing fatalities in humans who have been stung and do not receive treatment soon enough. Some researchers suspect that these jellyfish are responsible for the death of more humans each year than sharks. Very few jellyfish contain as potent a venom as the Box Jellyfish though.
Turtles and about 124 fish species have no issues consuming jellyfish as part of their diet. Humans also harvest a rough estimate of 470,000 jellyfish per year for consumption because of their fat- and cholesterol-free properties. Overharvesting does not appear to be a danger to jellyfish though. Jellyfish are an ancient species of marine life with a hardy survival rate.
The earliest jellyfish species appeared more than 500 million years ago, and to 0499this day, very few species of jellyfish fall on the endangered species list. The greatest danger posed to the jellyfish species is water pollution that either destroys the phytoplankton and larvae jellyfish feed off of, or outright kills developing jellyfish. Conservation efforts should best be focused on banning water pollution if populations appear to dwindle.
Jellyfish are easy to identify due to their gelatinous body and umbrella-shaped head, usually with tentacles trailing underneath or behind. The length of the tentacles, the size of the jellyfish, and the colors vary tremendously. Some appear almost invisible in the water from a distant, others are vibrant and impressive. From a safe distance, jellyfish can be beautiful to observe and soothing to watch moving through the water.