Jellyfish: Fascinating Creatures of the Sea

General Overview

• Habitat: Found globally in deep oceans and shallow coastal areas.
• History: Have existed for hundreds of millions of years.
• Physical Characteristics: Boneless, brainless, and bloodless; composed mainly of a jelly-like substance called mesoglia.
• Biological Classification: Not actual fish; they are invertebrates belonging to two different biological phyla.

Terminology

• Common Name: Jellyfish, but increasingly referred to as "sea jellies" to avoid confusion.

Unique Characteristics

• Immortal Jellyfish:
  • Species: Turitopsis dohrnii can reverse aging through a process called transdifferentiation.
  • Process: When stressed, can revert to a polyp and restart its life cycle.
• Reproduction:
  • Sexual reproduction through sperm and eggs in water.
  • Asexual reproduction by cloning or splitting.

Venom and Stings

• Most Venomous Species: Box jellyfish (Chironex fleckeri).
  • Tentacle Length: Can grow up to 10 feet long.
  • Effects of Sting: Can cause paralysis, cardiac arrest, or death within minutes.
• Annual Stings: Approximately 150 million reported jellyfish stings.

Biological Composition

• Water Content: Jellyfish are approximately 95% water.
  • For comparison, humans are about 60% water.
• Anatomy: Very basic structure without hearts, blood, brains, or bones.
  • Possess simple sensory organs and a basic digestive cavity (acts as stomach, intestine, and esophagus).
  • Upon washing ashore, jellyfish can evaporate rapidly due to high water content.

Groups and Behavior

• Collective Terms: Jellyfish groups are referred to as blooms, swarms, or smacks.
• Bloom Formation:
  • Can occur quickly, often for mating purposes.
  • Can become so dense that jellyfish outnumber water in a given area.
  • Size can range from a cubic meter to hundreds of square miles.

Ecological Impact

• Problems Caused by Blooms:
  • Clogging fishing equipment.
  • Damaging ships (e.g., in Mexico).
  • Closing beaches (e.g., in Australia and Europe).

Scientific Research

• Undiscovered Species: Scientists believe there may be as many as 300,000 undiscovered jellyfish species.