mystery of jelly fish

As summer approaches, more and more people come visit hometown, enoshima.

There is this big aquariumc called enoshima aquarium near the beach and there exists a variety of creatures.
And one of my favorite species is jelly fish!

Today, I would like to discuss a little bit of the mysterious eco-system and lifecycle of jelly fish.


Jellyfish have a complex life cycle: a single jellyfish reproduces both sexually and asexually during its lifetime, and takes on two different body forms.

An adult jellyfish is called a medusa, which is the familiar umbrella-shaped form that we see in the water. Medusa jellyfish reproduce sexually by spawning—the mass release of eggs and sperm into the open ocean—with entire populations sometimes spawning all together. Male and female jellyfish release the sperm and eggs from their mouths. In most species, fertilization takes place in the water; in others, the sperm swim up into the female’s mouth and fertilize the eggs within.

The fertilized eggs then develop into planulae, which are ciliated free-swimming larvae shaped a bit like a miniature flattened pear. After several days of development, the planulae attach to a firm surface and transform into flower-like polyps. The polyps have a mouth and tentacles that are used to feed on zooplankton.

Polyps reproduce asexually by budding—when a polyp divides roughly in half to produce a new genetically identical polyp—or they can produce or transform into medusae, depending on the type of jellyfish. Hydrozoan polyps bud medusae from their sides; cubozoan polyps each transform into a medusa.


Jellyfish play an important role in the oceanic food chain and the ecosystem. Jellyfish are carnivorous and feed mostly on zooplankton, comb jellies and other jellyfish. Large species of jellyfish feed on large crustaceans and other marine organisms. Sea turtles, sunfish and spadefish prey upon jellyfish. The cannonball and mushroom jellyfish are a delicacy in Asia.

In recent years, studies have suggested that when jellyfish blooms die-off, massive quantities of jellyfish sink out of surface waters and can deposit as “jelly-lakes” at the seafloor, choking seafloor habitats of oxygen and reducing biodiversity.
SO it is very important to protect jellyfish in order to maintain the biodiversity.


Ocean Portal

University of Hawaii: News



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