Chrysaora fuscescens Brandt, 1835
Sea nettles can swim against a current with the oral arms and tentacles extended. They move by means of jet propulsion: squeezing the bell, the sea nettle pushes water behind it, enabling it to move through the water column. Most of the time, however, they float largely passively.
As is the case for many jellyfish, reproduction includes a complex cycle of asexual and sexual phases.The complete life cycle of the Pacific Sea Nettle has been studied in detail at The Monterey Aquarium (California, USA), where these jellyfish have been maintained in captivity since the 1990s, and is described by Widmer (2008).
A related species, the Northern Sea Nettle (C. melanaster) is also found in the eastern Pacific, but usually occurs significantly farther north in the Bering Sea and Gulf of Alaska, although it may drift south at least as far as Oregon. It is similar to the Pacific Sea Nettle and has often been confused with it, but, among other differences, the Northern Sea Nettle has an exumbrella (upper, convex surface of the bell) that is pale white and the pale subumbrella (lower, concave surface of the bell) has 16 radiating dark streaks that are absent in the Pacific Sea Nettle (Carlton 2007). Martin et al. (1997) provide comparative descriptions of the Chrysaora species recognized as of 1997. Additional information on some of these species can be found in Larson (1990).
The Pacific Sea Nettle (C. fuscescens) is a large jellyfish with a bell of up to about 30 cm. in diameter. It has four long, spiraling tentacles surrounding its mouth that are known as “oral arms”. Around the perimeter of the bell are 24 marginal tentacles, organized in eight groups of three, which may trail several meters behind the bell. The exumbrella (upper, convex surface of the bell) is amber-colored and darkest near the margin (Carlton 2007).
Prey consumption by large medusae such as the Pacific Sea Nettle can have a major impact in structuring ecological communities (Brodeur et al. 2002; Brodeur et al. 2008). For example, in a a study in the Bering Sea, Brodeur et al. (2002) estimated that the Northern Sea Nettle (a close relative of the Pacific Sea Nettle) consumed a third of the standing stock of zooplankton during the summer season. Based on research focused on biologically rich coastal upwelling regions off the coast of Oregon and northern California, Suchman et al. (2008) and Brodeur et al. (2008) concluded that when the Pacific Sea Nettle and other medusae are seasonally abundant they have the potential to significantly deplete the standing stock of vulnerable prey and to compete with predatory fish feeding on similar prey items in the northern California Current.
The Pacific Sea Nettle is common off the coasts of Oregon and northern California, especially in late summer, fall, and winter. It is often encountered in aggregations just offshore and stranded on beaches.
A variety of hyperiid amphipod crustaceans may be closely associated (especially early in their development) with various types of gelatinous zooplankton, including medusae, ctenophores, siphonophores, and salps. The degree to which each hyperiid species is host-specific (i.e., restricted to just one or a few particular host species) remains unclear. Similarly, the question of the degree to which these associations are obligate (i.e., required for the hyperiid to complete its life cycle) remains controversial. The question of how much the hyperiids harm their hosts also remains controversial and presumably varies depending on the species involved (Gasca and Haddock 2004 and references therein). Hyperia medusarum and Lestrigonus shoemakeri are two parasites that may heavily infest the Pacific Sea Nettle in both the wild and in captivity (Crossley et al. 2009).
Larvae of Cancer gracilis crabs may be found hitchiking rides on Pacific Sea Nettles (Wrobel and Mills 1998 cited in Widmer 2008).
Suchman et al. (2008) analyzed the diet of the Pacific Sea Nettle off northern California and found that the eggs of euphausiid crustaceans (krill) were consumed at a disproportionately high rate relative to their abundance in the plankton. When euphausiid eggs were absent, gelatinous zooplankton were the preferred food. Only where both krill eggs and gelatinous zooplankton were scarce did the widely abundant calanoid copepods become the primary prey of the Pacific Sea Nettle. These differences in prey "preferences" may largely be a function of the relative difficulty of catching different prey (e.g., eggs that can't escape versus fast-moving copepods).
Pacific Sea Nettle stings rarely require medical attention, despite causing considerable pain and discomfort. However, at least one case of severe reaction has been attributed to multiple stings from this species (Burnett 2006). In recent years, laboratory and field trials of a commercially developed sting inhibitor have shown excellent promise in reducing both the frequency and severity of stings from Pacific Sea Nettlles, as well as some more dangerous jellyfish (Kimball et al. 2004; Boulware 2006). This product is reportedly based at least in part on the chemical properties of the mucus coating of clownfish (Boulware 2006), which protects the clownfish from the stings of the sea anemones with which they are closely associated.