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Freshwater jellyfish

Freshwater jellyfish

Freshwater jellyfish

(Craspedacusta sowerbyi)

Tags: Aquatic

Identification and Reproduction

Identification: 

  • Freshwater jellyfish is similar to other jellyfish, it is gelatinous and 99% of its body is composed of water. 
  • Most of the body is translucent with a white or green tinge. 
  • It lacks a head, skeleton and does not have distinct organs for respiration or excretion. 
  • It dimorphic and have two main stages; polyp and medusa morph. 
  • In its medusa morph it resembles a bell-shape, approximately 20-25 mm in diameter. In this mature form they bear numermous groups of tentacales around the margin of the "bell". The bell is a large stomach-like structure called a manubrium. The manubrium is composed of four distinct radial canals and one circular canal. 

  • Its polyp form is small, only measuring 2 mm tall, larva-like and lacks tentacles. 
  • They stinging cells at the end of their tentacles, nematocysts, are unable to penetrate human stings unlike marine jellyfish. 

Reproduction: 

  • Freshwater jellyfish will reproduce asexually when they are in their polyp stage, from budding. 
  • Polyps are small and collectively make up a colony, attached underwater to vegetation, rocks, and even tree stumps. 
  • Polyp buds will develop frustule buds that are apple to travel short distances and form a new polyp. 
  • Polyps can also be distributed passively via aquatic plants, aquatic animals and transfer from birds. Polyps can become dormant in winter and when conditions warm they can re-establish into active polyps. 
  • Medusa buds detach from mature medusa stage adults and will eventually form free-living adult medusas. They will reproduce sexually in this tage from fertilizd eggs. 
  • Sexual reproduction is very rare, often populations in a region are all male or all female.

Habitat & Ecology

  • Freshwater jellyfish is present on all continents except for Antarctica. 
  • It occupies freshwater lakes, reserviois, man-made ponds, water-filled pits, rock quarries, algae-filled ponds and rivers. 
  • It prefers calm waterbodies. 
  • They are often found at the bottom of shallow waters to help conserve energy and a way to escape predation. 
  • They consume zooplankton. 
  • Populations of freshwater jellyfish in medusa form are somewhat unpredictable.

Impacts

  • They can alter aquatic ecosystems. 
  • They can invade in large populations and consume an abundance of zooplankton. 
  • May compete with native aquatic species for food and other resources. 

Management

  • Always clean, drain, and dry aquatic equipment and watercraft before transferring from one body of water to another.
  • Report any sightings of the freshwater jellyfish. 

Resources

For more information on how to identify freshwater jellyfish refer to the Animal Diversity fact page on Craspedacusta sowerbyi

BCLSS also provides a data page on freshwater jellyfish here.

Header photo (CrazyBiker 84).