Thursday, March 10, 2011

A Field Guide to Dead Sea Jellies of the Gulf of Alaska

Photographing a Lion's Mane Jelly at Tonsina Beach, near Seward, Alaska

Observation of dead sea jellies can be an enjoyable summer pastime.   Hopefully, this guide will provide some insight into what these gobs of goo on the beach are, and provide the sea jelly observer with some hints on identifying the species of jelly found.   One note of caution: sea jellies contain nematocysts, or stinging cells; these cells are capable of stinging even after the animal has died.   Attempting to touch sea jellies, even dead ones, is not recommended.

Moon Jelly

Moon jellies (Aurelia aurita) are one of the most commonly seen species of dead sea jellies to be seen in Alaskan beaches, and become increasingly plentiful as the summer progresses.   These jellies are also referred to as saucer or common jellies.   They are easily identified by their translucent appearance, and the presence of four white, horseshoe-shaped gonads in the center of the body.   The largest Moon jellies can reach the size of a dinner plate.    After a few days of desiccation, the dead Moon jellies often take on the appearance of discarded plastic soda lids.   It is thought that Moon jellies have a lifespan in the wild of approximately six months, although in captive settings this species is capable of living for several years. Although Moon jellies lack the long, trailing tentacles seen in most sea jelly species, they are capable of stinging, however the sting is considered very mild.   On occasion, female Moon jellies can be identified by the masses of fertilized eggs hanging from the arms.

Sea Nettle, with kelp
  Pacific Sea Nettles (Chrysaora fuscescens) are both large and colorful, with amber–tinted bells growing as large as three feet in diameter, and tentacles as long as 12-15 feet.   When observed in the water, sea nettles commonly pulse against the current, with their brown tentacles and lace-like oral arm widely flared.   Dead Sea Nettles can most easily be distinguished from dead Lion’s Mane jellies by the presence of amber lines radiating outwards from the center of the body.   These amber lines are more distinct in sea nettles that inhabit higher-salinity parts of the ocean.    Certain Pacific Sea Nettles also exhibit a star-like pattern across the top of their bell.   

Lion's Mane Jelly
  Lion’s Mane Jellies (Cyanae capillata) are the largest species of sea jelly in the world, and the only species of sea jelly to feature in a Sherlock Holmes mystery.    Their large size and brilliant coloration make them one of the most easily spotted species of dead sea jellies.   Their coloration tends towards pinks, purples, oranges and ambers, with younger individuals tending to be more orange.   Specimens seen on beaches can easily reach two to three feet in diameter.   (The largest Lion’s Mane ever recorded had a bell diameter of over seven feet.) The tentacles of the Lion’s Mane are much more numerous than in the Sea Nettle, with the oral arms being both wider and shorter.   Lion’s Mane jellies have an eight-lobed body; on some specimens, this can result in a spoke or sunburst pattern, as seen above.

Egg-Yolk Jelly, courtesy Steven G. Johnson, Wikipedia
The Egg-Yolk Jelly (Phacellophora camtschatica) is another large jelly occasionally seen in Alaskan waters.   The name derives from the yellow gonad mass surrounded by a cream or yellowish bell.   These bells are divided into sixteen segments, observation of these spokes is a good way to distinguish it from Lion’s Mane jellies, whose bells have only eight spokes.   If seen in the water, the Egg-Yolk jelly only rarely or weakly pulses, preferring to float in the water column like a gelatinous drift net.

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