Sea nettle

Chrysaora quinquecirrha

ORDER

Semaeostomeae

FAMILY

Pelagiidae

TAXONOMY

Chrysaora quinquecirrha Desor, 1848, Nantucket Bay, Massachusetts, United States.

OTHER COMMON NAMES

None known.

PHYSICAL CHARACTERISTICS

The swimming bell may reach 10 in (25 cm) in diameter, but medusae generally are much smaller. The edges of the swimming bell appear scalloped, with 16 or more lappets. One large tentacle emerges from between every other lappet, and twice as many small tentacles arise from beneath the lappets. Eight rhopalia are present in alternate clefts between lappets. The narrow oral arms are long and diaphanous. Medusa color ranges from milky white to white with radiating purplish red stripes on the bell.

DISTRIBUTION

This species is found near shore in temperate to subtropical Atlantic Ocean waters of North, Central, and South America above the equator and in the Gulf of Guinea and Angola, Africa. They also are reported from the western Pacific Ocean in the Philippines, southern China, Malaysia, and the Bay of Bengal.

HABITAT

Medusae are most abundant during the summer in estuaries, where they thrive at salinity levels as low as 7 ppt. In Chesapeake Bay unusually low salinity levels in spring result in fewer medusae, with the distribution shifted to waters of higher salinity.

BEHAVIOR

The medusae swim constantly in slow circles, owing to the drag of their oral arms and tentacles. As seems to be true for other scyphomedusa species, the sea nettle feeds continuously.

FEEDING ECOLOGY AND DIET

This species has been studied extensively in Chesapeake Bay and its tributaries, where it occurs in great numbers. When they are abundant, medusae may reduce copepod populations. This species also feeds on comb jellies (Mnemiopsis leidyi) and can eliminate them from tributaries. Bay anchovy (Anchoa mitchilli) spawns during peak medusa abundance, and medusae may eat 50% of the fish eggs and larvae daily, on average. Surprisingly, the polyps eat and digest oyster larvae (veligers), but the medusae do not digest them.

REPRODUCTIVE BIOLOGY

The life cycle is typical of semaeostome scyphomedusae, having both a polyp and a medusa stage. In temperate Chesapeake Bay, the polyps become dormant during the cold winter months. They excyst and undergo strobilation in spring when water temperatures exceed 60°F (17°C). More ephyrae are produced at salinity levels between 10 and 25 ppt than at lower or higher salinity levels. Spawning takes place around dawn. Larvae are not brooded by the females.

CONSERVATION STATUS

Not listed by the IUCN.

SIGNIFICANCE TO HUMANS

This species was so abundant in Chesapeake Bay during the 1960s that a legislative bill was passed to provide money for research on it. The medusae have an irritating sting, which deters swimming, especially in the shallow tributaries where they are most abundant. The species may be of overall benefit in the food web, by controlling populations of comb jellies, which consume oyster veligers and much more zooplankton than do the medusae. Thus, more zooplankton may be available for zooplanktivorous fishes, such as bay anchovy, which are prey for favorite sport fish, such as striped bass and bluefish. ♦

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