Cannonball jellyfish are a common sight in many coastal waters, recognized by their distinctive shape. These marine invertebrates often draw curiosity, particularly regarding their potential threat to swimmers. This article clarifies common misconceptions about their characteristics and interactions with humans.
The Nature of Their Sting
Cannonball jellyfish (Stomolophus meleagris) possess stinging cells called nematocysts. Their sting is generally very mild, posing little harm to humans. Contact typically results in minor skin irritation, described as a slight itching or mild burning sensation. The affected area may show redness and slight swelling, but these symptoms are usually short-lived.
Their stinging mechanism primarily captures small prey like zooplankton, fish eggs, and larvae, not for defense against larger animals. When disturbed, cannonball jellyfish can secrete a toxic mucus. The sting’s mildness is due to their venom’s weaker potency and smaller stinging structures, which typically do not penetrate human skin deeply.
While contact is usually benign, rare instances exist where the toxin can lead to more noticeable effects. Some individuals might experience minor eye irritation if they rub their eyes after touching a jellyfish. In very uncommon cases, the toxins have been linked to cardiac issues, such as irregular heart rhythms, in both humans and animals.
Identifying and Encountering Cannonball Jellyfish
Cannonball jellyfish are identified by their firm, dome-shaped bell, resembling a cannonball, which gives them their common name. Their bell typically measures 7 to 10 inches wide and is about 5 inches tall. They often appear milky, whitish, or yellowish, frequently with a brown pigment bordering the rim. Pacific populations can exhibit bluish or gray coloration.
Unlike many other jellyfish, cannonball jellyfish do not have long, trailing tentacles. Instead, they feature short, complexly branched oral arms located underneath their bell. These oral arms are covered with mucus, aiding in trapping the small organisms they consume. They are abundant along the southeastern U.S. coast, including the Gulf Coast, and also found in the western Atlantic, eastern Pacific, and western Pacific oceans. They prefer estuaries and saline waters near shorelines, with optimal temperatures ranging from 20.3 to 24.5 degrees Celsius.
These jellyfish are frequently encountered during seasonal blooms, particularly in the fall and summer months in the southeastern U.S. They can sometimes wash ashore in large numbers, especially after storms. When encountering cannonball jellyfish, observe them from a distance and avoid direct contact. Even if a jellyfish appears dead, its stinging cells can remain active and potentially cause mild irritation upon touch.