|Pleurobrachia bachei A. Agassiz, 1860 : Sea gooseberry
Phylum Ctenophora / Order Cydippida / Family Pleurobrachiidae
The sea gooseberry is among the more common comb jellies of the West Coast. When held out of the water, the gelatinous body does indeed resemble the fruit known as a gooseberry. The spherical body, length to 15 mm, possesses 8 evenly spaced comb rows that extend nearly the entire length. A pair of long tentacles originate from short tentacle bulbs that are situated close to the pharynx. Numerous sticky side branches on the tentacles ensnare zooplankton prey when fully extended. The comb rows are used to propel the jelly slowly forward as it fishes for prey. Captured prey are brought to the mouth on the other side of the body by a spinning action that is easily observed in captivity. Prey include copepods, larval fish, various types of eggs, and small crustaceans.
Pleurobrachia is seasonally one of the dominant predators in California waters, and may regulate the abundance of certain zooplankton prey. They are hermaphrodites and incredibly prolific – an adult can release up to 1000 eggs per day, and breeding can occur at all sizes. As a result, massive increases in population density can occur within inshore areas in a matter of days. Among the sea gooseberry’s more dangerous threats is the voracious comb jelly Beroe, which slurps up whole comb jellies with its cavernous mouth. When a potential predator is detected, the direction of the comb row beat can be reversed, sending the sea gooseberry off in another direction and hopefully out of danger.
Although not always seen during excursions into Monterey Bay and other West Coast locations, during spring and summer months, Pleurobrachia can be incredibly abundant in surface waters. Due to the transparent body, they often are not easily seen in the water, but with a surface plankton tow the net may be totally packed after only a few minutes. P. bachei ranges from Alaska to Mexico; other closely related species of Pleurobrachia are found in the Atlantic Ocean and other temperate seas. The genus name (Pleurobrachia) is derived from the Greek, pleura (side) and brachion (arm). Sea gooseberries do well in captivity when maintained in a kreisel and fed brine shrimp nauplii and wild zooplankton, and are a popular display at public aquariums featuring jellies.