Fig. 1.  Seasonal bloom of jellyfishes Aurelia labiata in Indian Arm, British Columbia.  The dark rings are gonads

There are only some 200 species of jellyfishes¹ throughout the world's² oceans, but their large size, abundance³, and stinging tendencies belie their small taxonomic representation.  The total includes about 50 species of sessile jellyfishes. Some 28 species of scyphozoans are known from Alaska to southern California (4 from San Juan Island, Washington), with Chrysaora fuscescens being one of the most common semaeostomes. Larson 1990 Bull Mar Sci 47: 546; Mills 1981 The Wasmann J Biol 39: 6; Reum et al. 2010 Northwest Sci 84 (1): 131.

NOTE¹  in the ODYSSEY the term “jellyfish” is used exclusively for the medusa stage of Class Scyphozoa, also known as scyphomedusae.  This may be a bit old-fashioned, as it goes against a trend in the scientific literature to include the medusae of Class Hydrozoa also as “jellyfishes”.  There is nothing right or wrong about either classification, but keep it in mind.  In the ODYSSEY the medusae of hydrozoans are referred to as hydromedusae.

NOTE²  most species of semaeostome jellyfishes have worldwide distributions, and a species like Aurelia aurita may be found in such diverse regions as Europe, Japan, Polynesia, North America, and Russia, and is common in brackish-water environments such as the Baltic and Black Seas. It does not, however, inhabit the west coast of North America. The common species here is Aurelia labiata  (Fig. 1) with, based on recent molecular evidence, the occurrence of a cryptic species tentatively named A. limbata in southern California. There are many scientific works on the distribution and biology of these cosmopolitan jellyfishes, but few done on west-coast populations.  It has been difficult to winnow out which of these publications would be useful inclusions in the ODYSSEY, so be mindful of this as you read through the selections.

NOTE³  a phenomenon of increasing interest is the worldwide proliferation of jellyfish, including the displacement of local species by non-indigenous species. Many scientists are concerned that jellyfish blooms may be occurring in response to the cumulative effects of anthropogenic changes in ocean conditions. Examples of west-coast blooms include those of jellyfishes Chrysaora melanaster and, to a lesser extent, Cyanea capillata in the Bering Sea, and invasions of several species of indigenous Black-Sea hydromedusans into San Francisco Bay.  Blooms of Aurelia spp. are common in many locations where they may interfere with water flow into coastal power plants and with net fishing. Our knowledge of the population ecology of jellyfishes, hydromedusae, and ctenophores is so scanty that scientists cannot presently distinguish between natural short-term fluctuations and possible long-term irreversible changes. Jellyfishes may be low in phylogenetic standing, but they feed high on the food chain, and commonly compete directly with fishes for food.