One of the most appealing things about visiting Oahu is its stunningly beautiful beaches. Situated in the Pacific Ocean, it has 227 miles of coastline and a beach for every type of traveler, including the popular snorkeling destination Hanauma Bay.
Oahu’s beaches are unmatched from the world-famous Waikiki Beach to secluded coves and hidden bays.
In addition to its beaches, Oahu is also home to a vibrant nightlife scene.
Whether you’re looking for lively clubs or more laid-back bars, you’ll find it all on Oahu. Also, Oahu is home to the only royal palace on American soil.
But if you’re planning on enjoying the water, you might ask: Does Oahu have jellyfish? Is it safe to swim and how common are jellyfish stings in O’ahu, Hawaii?
Jellyfish are a common sight in the waters around O’ahu, Hawaii — particularly during and following a full moon. In fact, jellyfish numbers have been rising in the area and the threat of serious stings from box jellyfish has been known to close certain beaches in Oahu during swarms; especially Southern facing beaches.
The types of jellyfish you might see in Oahu are:
- Box jellyfish (several species)
- White-spotted jellyfish
- Spotted jellyfish
- Portuguese man o’ war (not technically a jellyfish!)
- Sea lice
- Moon jellyfish
- And Carybdea sivickisi
Let’s take a closer look at these species, jellyfish calendars and season for O’ahu, jellyfish stings, and more.
Types of Jellyfish in Oahu, Hawaii
Let’s take a look at some of the most common species of jellies in and around the waters of O’ahu.
Oahu is home to a few different kinds of box jellyfish including winged box jellyfish and jimble jellyfish.
They are in the Cnidaria family, which includes other species like corals. Their tentacles are lined with stinging cells called cnidocytes, and each of these cells has a thread called a nematocyst.
Out of all jellyfish, their stings have some the most potent poison.
Also, this type of jellyfish has eyes capable of detecting light.
Box jellyfish can have long tentacles that can reach up to 15 feet in length, however most of the species found near Oahu are much smaller. They are often found near the shore in areas with high cliffs or rocky coasts.
They are also called Cubazoan due to their box shape. An interesting fact about them is that they actually have 24 eyes that circle around the perimeter of their bell.
When touched, their tentacles will release a toxin that can cause severe pain, swelling, and redness. Also, the stinging portion of their tentacles covers the entire surface area of the tentacles.
The white-spotted jellyfish, or Phyllorhiza punctata, is the most common type of jellyfish seen in Waikiki and Oahu.
They are in the same family as the Carybdea Alata, or the box jellyfish. It has a large bell that can span up to 50 cm.
On Oahu, they live in the Ala Wai Canal and Yacht Harbor, Pearl and Honolulu Harbors, and Kaneohe Bay.
They are an invasive species from Australia.They are found in all of the Hawaiian Islands, as well as in many other parts of the world. They are usually seen near the shore in areas with high cliffs or rocky coasts. These jellyfish can range in size from 2 inches to 6 feet long.
Although they are not aggressive, they can sting if they come into contact with humans. The sting is not usually severe and will usually only cause redness or swelling.
Another name for the spotted jellyfish is the lagoon jellyfish, and its scientific name is Mastigias Papua.
This type is small, with a maximum size of just under four inches.
They have small spots on their bell that is brown and yellow.
However, this type of jellyfish gets most of its food from the sun and does not need to sting.
Portuguese Man o’ War
The man o’ war , also known as Physalia physalis, is not actually a true jellyfish. It is a siphonophore, which is an animal made up of many small individuals called zooids.
These zooids work together and are unable to survive on their own. Each zooid has a specific task, such as swimming or catching prey.
The man o’ war gets its name from its large sail-like float that helps it drift along the ocean’s surface.
These jellyfish can be found all over Oahu, but they are most commonly seen in Waikiki Beach and Hanauma Bay.
They can range in size from 2 inches to 6 feet long. They cannot swim and instead float with the sea currents.
Their venom is quite toxic and painful, though rarely fatal.
Hawaiian Sea Lice
This type of species is a type of jellyfish larvae. They are too small to see, and they result in a burning or rash sensation when humans make contact.
Expect to feel the reaction to their sting hours after contact.
The moon jellyfish, or Aurelia aurita, is a completely harmless type of jellyfish found in Hawaii.
They get their name because they are shaped like the moon. Their size ranges between 10 to 16 inches. With translucent, purple, or bluish bodies, they are easy to identify.
You can see a number of pink or purple circles inside of the bodies.
Moon jellyfish have a flat and round shape. There is a curve at the base on the edges, so they resemble a frisbee.
Underneath their bodies are tentacles, but moon jellyfish deliver only an extremely mild sting.
This species of jellyfish, in the same family as the white-spotted jellyfish, has only been seen active at night.
It is very small. Also, it only has four tentacles. At its largest, it is less than half an inch in length. It has a translucent, bell-shaped body. And it drifts near the surface of the ocean in large groups.
It is found off the coast of Hawaii, including in Oahu.
This type of jellyfish is not known to sting humans.
Jellyfish Season & Calendar in Oahu, Hawaii
Jellyfish, particularly box jellyfish, can dependably be seen near the beaches of O’ahu about eight days after the full moon.
The beaches will have signs alerting visitors of the potential jellyfish stings. During times of year where they are especially abundant, such as February, the beaches may be closed.
However, their numbers have been steadily increasing in number, and the frequency of their stings have become more and more common.
Jellyfish mate year round in the beaches. Their patterns are fairly predictable, being on and around the full moon, and up to five days afterward.
Because of high jellyfish numbers, beaches on Oahu are frequently closed.
In March, the state issued a public emergency alert before shutting down the beach.
How Common are Jellyfish Stings on Oahu?
On days when the jellyfish are swarming, more than 100 jellyfish stings can occur in one day in Oahu.
This news report cites up to 120 stings in a single afternoon!
Nearly every sting is attributed to the box jellyfish or sea jelly as it is sometimes called.
Other jellyfish are common in the area but far less likely to sting, and even then, the stings are quite mild.
Before swimming, be sure to talk to any lifeguards on duty to see if they have information about jellyfish in the area.
They normally have up to date information. Also, you can look at the available jellyfish calendars and see where your visit lands.
Overall, jellyfish are a consideration if you plan on visiting O’ahu. Their numbers have climbed in recent years, and during swarms, stings are extremely common.
Avoid the water near a full moon for your best chance at a sting-free swim. It’s also a good idea to keep or pack some vinegar to treat stings, if needed!
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Hope this helps!