What Do Jellyfish Have to Do With the Moon?

Ethereal and semi-transparent, jellyfish can be amazing to see while diving, but not so much fun to get stung by. Closer to shore, groups of jellyfish (called a bloom, a swarm, or a smack) can swarm in the thousands. Scientists have found a correlation with the lunar calendar in determining when jellyfish arrive in nearshore waters. In Hawaii that’s about 8-10 days after a full moon, or around the end of this month. Beachgoers may see signs at beaches warming of box jellyfish and divers may encounter a jelly or two while diving.

However, the appearance of jellies may have more to do with the tides, which ebb and flow with the moon. One theory is the jellyfish ride high tides into shore, where some end up in shallow depths and on the beach.

Jellyfish in Hawaii

There are several types of jellyfish in waters around Hawaii including the box jelly, moon jelly, and spotted jelly. None of them are deadly, and most swarms affect beach goers more than divers. This article describes each of these types so that you will be able to identify them if you should meet one while in the waters of Maui, how to protect yourself while scuba diving, and what to do should you get stung.

Box Jellyfish. A box jelly’s bell has four distinct corners, giving it a boxy shape.  It’s body measures one to three inches, with stinging tentacles up to two feet long. A sting from a box jellyfish can be quite painful, and should be avoided. Unlike other jellyfish that can only detect up and down motions, the box jelly has 24 actual eyes. Eyes are grouped in clusters around its bell, giving it a 360 degree view of the environment.

Moon Jellyfish. The moon jelly is rather benign as far as stings go, with mild stinging cells. With a translucent white, saucer-shaped bell above, and lacy fringe-like tentacles below, Moon jellies are beautiful to watch in the water. They grow to between 10–16 inches across and are recognized by the four horseshoe-shaped gonads that can be seen through the top of their bell. They munch on micro-plankton, tiny crustaceans, and fish larvae.

Spotted Jellyfish. The spotted jellyfish has a high, rounded translucent bell with polka dots that averages 4 inches in diameter but can grow up to a foot. It is typically seen as greenish brown in color due to its symbiotic relationship with zooxanthellae algae in its tissues. “Arms” hang below the bell, each with several small mouth openings to capture plankton. Clublike appendages hang down below the arms.

Portuguese Man-O’-War. Many don’t know the Portuguese Man-O-War is actually not a jellyfish, but a related member of the same phylum. They are common here in Hawaii and pack a painful sting. The Portuguese man-o’-war is stunning to look at, with a bright blue body and clear sail, which it uses to propel itself along the ocean surface. Long, purplish tentaclesstretch below the water up to 30 feet long.

What to do if stung by a jellyfish

There are solid strategies divers can undertake to remedy a jellyfish sting. However, let’s dispel one common myth upfront: Don’t pee on a jellyfish sting. Not only is that pretty gross, it may worsen the sting. Jellyfish tentacles have stinging cells called nematocysts that contain venom. Brushing up against a jellyfish activates these stingers. Peeing on the sting could cause the cells to release more venom.

There are varying opinions on how to properly treat a jellyfish sting, but one thing is consistent- you want to avoid activity that make matters worse, such as don’t rinse with fresh water. Applying a wash of white vinegar, then removing tentacles with tweezers and applying heat is most often recommended. See this article by Maui Ocean Center for more information, based on a University of Hawaii study.

Preventing a sting

Ideally, you won’t ever experience a jellyfish sting by taking advanced precautions. To prevent a sting simply avoid skin contact with a tentacle. We assume one wouldn’t purposely reach out and touch a jellyfish. Most stings occur by unknowingly brushing up against one. Wear a full-body wetsuit, or a thin skin in warmer temperatures. Even something as thin as a Lycra provides a thick enough physical barrier to protect you from stings and other scrapes.

Climate resilient survivors

Jellies have a short lifespan, but are also very resilient. A lot of Hawaii sea life love to munch on jellies, including various fish, sea turtles (especially the leatherback), some seabirds, whale sharks, crabs and humpback whales. Even though voraciously eaten by other marine life, their numbers have increased while predators decreased. Climate change and other environmental factors don’t seem to affect these creatures either. Jellyfish thrive in areas where there is an abundance of pollution and very little oxygen.