Wildlife of the Week!

© Moon Jellyfish are spotted swimming in their tank at the Shaw Centre for the Salish Sea.

Welcome to Wildlife of the Week, where we will highlight another fascinating marine creature! We have chosen a creature similar to an animal we have discussed before (remember: the Fried-Egg Jellyfish)? Both creatures are gelatinous invertebrates and true jellyfish. To be plankton, like all jellyfish are, you must not be able to swim against the direction of a current. Though they can swim and move via their large circular “bell”, jellyfish like this Moon Jelly(fish) are ultimately at the mercy of where the ocean carries them. But can the Moon Jelly sting? To find out, read on with our blog at www.5starwhales.com

There have been different forms and species identified within the “Moon Jelly” name. A Moon Jelly commonly found in B.C. (but not limited to this area) is referred to as Aurelia labiata, whereas the arguably more global common Moon Jelly is known as Aurelia aurita

All Moon jellies can grow between 10-40 cm long (width of circular bell) and are almost completely transparent as well as symmetrical. However, food ingested can alter the colour of the bell. The Aurelia l. species does not have tentacles, but other Moon jellies have relatively short and fine tentacles, at about 1-5 cm long. There are also four larger oral arms that are used for predation to sting and capture prey. A third set of tiny extensions called cilia (around the perimeter of the bell) also assist with feeding tasks. The Moon Jelly’s circular bell is round and medusa-shaped; though mostly transparent, the gonads that are located in the center (appear like horse-shoes or crescents), give rise to a variety of colours in the centre of the bell. 

Without a digestive, nervous or circulatory system, the Moon Jelly has a very simple body plan. It does, however, have a mouth which is located on the underside of the bell. Special digestive tissue helps to digest meals and nutrients. 

The Moon Jelly, in its various species, have been found in all the world’s oceans except that of the Arctic. Moon Jelly Aurelia l. can be found from Alaska to California (as well as on North America’s east coast) but has been known to dwell elsewhere in the world (Europe, Japan). Moon jelly Aurelia a. mostly congregates in the Atlantic and Indian Oceans as well as the Pacific Ocean. Other areas include Australia, Madagascar, and South America. The Moon jelly seems to prefer coastal shallow pelagic waters, and areas such as bays and harbours. However, they have been spotted at deeper depths of 200-1,000 m. The Moon jelly thrives when in low salt content water (often brackish), and physical growth and size is determined by salt content and ideal water temperature. 

The Moon Jelly Aurelia l. captures prey with its bell covered in sticky mucous, as it lacks tentacles as mentioned. Other Moon jellies typically use their stinging tentacles to capture prey, as well as using mucous to trap food. Once brought to the mouth, other small extensions as well as their oral arms help to move the prey through canals leading to the stomach. Moon jellies have a diverse, carnivore diet of other plankton (e.g. larvae, copepods), small fish and even other jellyfish. 

As with many other jellyfish and jellies, the Moon Jelly has a series of life stages before reaching adult form. To reproduce, the Moon jelly is typically between 4-12 months old. Reproduction is not specific to time of year, but will depend on surrounding conditions and reproductive episodes for Moon jellies may last for several months. Genetic material released by males into the water will fertilize eggs within the females’ gastric pouches; after this event the larvae will be released and settle towards the substrate. From here, thee live as a sessile (“in-place”) polyp for up to 25 years, and will release free-floating clones of themselves (ephyrae) which will grow into adult jellyfish. 

Moon jellies are often spotted in a horizontal position so that they can stretch out with all of their tentacles (or bell) and capture as much food as possible! Moon jellies have organs that can help them to determine their depth and position. Depending on ocean and environmental factors, large swarms can be spotted together, of up to a thousand individuals. It has even been thought that they communicate via chemical means with one another. 

Moon jellies are preyed upon by a number of ocean species, namely fish, birds, turtles and other jellyfish. Luckily for the Moon jelly, they have a simple “eye” of sorts that can help them to manage their depth with light changes, helping them to avoid “risky” predation times. When there are lots of prey, Moon jelly populations do very well. 

Moon jellies play an important role in moving energy and carbon throughout the food chain, as they feed on some of the smallest creatures in the ocean and feed larger animals. They also serve as an important food item for Sea turtles, unfortunately often being confused for pollution like plastic bags. With extreme population numbers however, Moon jellies and other jellyfish can cause problems for human fisheries, tourism and other facilities. A helpful protein in Moon jellies has been studied for pharmaceutical purposes. The Moon jelly is therefore an important, yet precarious member of many ocean systems. 

There is so much more to know about this critical player in the marine world; try out some trivia below if you are feeling especially confident with your Moon jelly knowledge! 

  1. True or False? Moon jellies have been to space. (ANS: True. Moon jellies were used in a 1991 study on weightlessness on board the Columbia space shuttle). 
  2. A Jellyfish is composed of ______% water. (ANS: 95%). 
  3. The Moon jelly is also known as the ______ or the ________ (ANS: Saucer jelly, Common jelly). 

BONUS CHALLENGE: 

Can the Moon Jelly sting a human?

Somewhat. Although their stinging cells may cause a rash or irritation to a human, the sting is generally nothing harmful or worrisome. These stinging cells can be lethal to animals with thinner skin however, such as small fish. 

Authored By: Alexa Desautels, B.Sc./ Five Star Whale Watching

To learn more, visit our References below! 

  1. “Aurelia aurita, Moon jellyfish”. Animal Diversity Web. University of Michigan Museum of Zoology: University of Michigan Museum of Ecology and Evolutionary Biology. 2020. ADW: Aurelia aurita: INFORMATION (animaldiversity.org)
  2. “Fried Egg Jellyfish”. OCEANA. Fried Egg Jellyfish | Oceana
  3. In Klinkenberg, Brian. “Aurelia labiata. Chamisso and Eysenhardt, 1821. Moon Jellyfish. Family: Ulmaridae”. E-Fauna Electronic Atlas of British Columbia. University of British Columbia. 2019. E-Fauna BC Atlas Page (src: AtlasAccordian) (ubc.ca)
  4. Fretwell, Kelly and Starzomski, Brian. “Moon jelly: Aurelia labiata: Heiltsuk/Haitzaqv: Hauqvayax”. Biodiversity of the Central Coast. The Starzomski Lab. The University of Victoria. Hakai Institute. 2013. Moon jellyfish • Aurelia labiata – Biodiversity of the Central Coast (centralcoastbiodiversity.org)
  5. “Moon jelly”. Biology. Lamar University. Moon Jelly – Lamar University
  6. “Moon jelly”. Encyclopædia Britannica, Inc. Moon jelly | jellyfish | Britannica
  7. “Jelly Alert! Moon Jellyfish – How to Spot Them & What to Do if You Get Stung”. Cannons Marina. Aug 31 2015. Jelly Alert! Moon Jellyfish – How to Spot Them & What to Do if You Get Stung – Cannons Marina
  8. “Jellyfish and other zooplankton”. Woods Hole Oceanographic Institution. Jellyfish & Other Zooplankton – Woods Hole Oceanographic Institution (whoi.edu).