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Jellyfish Gone Wild — Home
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Jellyfish Gone Wild — Text-only | Flash Special Report
Reproduction


THE HOLY GRAIL TO UNDERSTANDING JELLYFISH BLOOMS

JELLYFISH REPRODUCTION:
Many jellyfish species reproduce extraordinarily quickly. How? By using a peculiar combination of sexual and asexual reproduction involving these steps:

1. Eggs and sperm are released by adult jellyfish--sometimes at incredible rates. For example, jellyfish known as sea nettles that live in the Chesapeake Bay may each shed 40,000 eggs daily.

2. A jellyfish egg unites with a jellyfish sperm to produce a larva.

3. Each larva attaches to a hard surface, such as a rock or an artificial structure like a drilling rig, at the ocean bottom.

4. The larva lives as a stationary polyp at the ocean bottom. Although much about polyps --which have only rarely been found in the wild--remains mysterious, scientists suspect that they may simultaneously blanket large expanses of ocean floor. They also suspect that polyps may opportunistically extend their polyp phase from days to even years or decades until conditions, such as temperature and food, are favorable to their survival as adults.

5. Once conditions become favorable, each polyp elongates and then buds off and releases many young jellyfish. A single polyp may thereby, by itself, reproduce large numbers of jellyfish.

What’s more, individual polyps probably don’t churn out young jellyfish in isolation. Rather, fields of polyps probably simultaneously transform into veritable jellyfish factories, mass producing tens of thousands of jellyfish at a time. Swarms of young jellyfish may thereby quickly form when their survival prospects are best.

6. Each young jellyfish rapidly develops into an adult jellyfish, and the cycle repeats.

Desperately Seeking Polyps: Because of the importance of polyps to the formation of jellyfish swarms, scientists are currently working feverishly to find polyps in the wild. “To understand jellyfish blooms, we must find those polyps,” affirms Lorenzo Ciannelli of Oregon State University.

But searching for tiny, transparent polyps on the ocean floor is like searching for the proverbial needle in the haystack. So researchers are currently using computers to simulate the drifting of young jellyfish from suspected locations of polyp colonies in the Bering Sea--a jellyfish hot spot where polyps have never been observed--to areas in the Bering Sea where adult jellyfish are known to swarm. Such analyses are designed to help identify the probable locations of polyp colonies, which may eventually be searched via remotely operated robots.

COMB JELLY REPRODUCTION:
Comb jellies--jellyfish-like creatures that are not true jellyfish but behave like jellyfish--also reproduce quickly. But they have a different reproductive cycle than jellyfish.

Each comb jelly is a self-fertilizing hermaphrodite that releases both eggs and sperms. An egg and sperm unite to form a fertilized egg that becomes an adult comb jelly without a polyp stage.

Some species of comb jellies, such as the widely distributed Mnemiopsis, reproduce quickly because: 1) individuals may start reproducing within days of being born; and 2) an adult may release 8,000 eggs and sperm per day.

Illustration Credit: Zina Deretsky, National Science Foundation