Siphonophores of the Pacific, with a review of the world distribution

Author(s): Alvarino, Angeles | Abstract: Most of the published work on Siphonophorae deals with taxonomic descriptions, taxonomic problems and systematic accounts, histology and anatomy and also gives records concerning the distribution of the individual species. Although the Siphonophorae are not so distinctly restricted to water masses as are most of the Chaetognatha species, it has been observed that some species of siphonophores can be used as indicators of the flow of certain types of waters into a particular region. Russel (1934) observed Muggiaea atlantica at the entrance of the English Channel where it "occurred for an unbroken series of years from 1913 to 1924 (excepting 1915, when none were seen in the collections), but that in 1924 Muggiaea kochi first made its appearance and that since that time Muggiaea atlantica has disappeared from the area. " Later I studied the plankton of this region and became familiar with the fluctuations in the occurrence of one or other of these species; the presence of Muggiaea kochi is an indication of the inflow of water from the south. Moore (1953) has considered that fluctuations in abundance are in part due to "inherent seasonal changes within a given water mass, but in part also to seasonal changes in the water mass present. " He has implied that in the Bermuda region the summer water of northern origin brings into the region species typical of colder regions, while the winter water comes from warmer locations in the south. He also states that in the Florida Current off Miami there is "a fluctuating amount of water of the Gulf of Mexico origin intruding into the main water mass. " He ends his discussion stating: "Although the abundance of several [species] has shown to be different in the Yucatan and Gulf of Mexico waters, none are completely restricted to one mass, and so readily useable as indicator species. " In the California region it has been observed from the monthly 1954 and 1958 California Cooperative Oceanic Fisheries Investigations cruises that Chelophyes appendiculata (a species typical of the temperate regions) is displaced by Chelophyes contorta (a warm-water species) with an inflow of warm water. A particular pattern of distribution was observed for Chelophyes appendiculata, Chelophyes contorta, Muggiaea atlantica and Muggiaea kochi off the Panama Canal in the Caribbean and Pacific regions. The material to be considered here consists of the extensive collections of Scripps Institution of Oceanography in the Pacific and the CalCOFI cruises in the region of the California Current and the Sea of Cortes. The material collected in the Pacific extends over a period of fourteen years (table 1). The present work provides the first extensive survey of the distribution of the siphonophores in the Pacific as well as a preliminary account of their bathymetric distribution. Bigelow (1911a) has presented extensive data from the Eastern Tropical Pacific and also from the Northwest Pacific (Bigelow, 1913). Table 2 includes other collections analyzed by the author. The published data on the distribution of the species observed in the Pacific and adjacent seas are compiled in table 3. Table 4 is a compilation of all published data on the bathymetric distribution of the species of Siphonophorae plus the author's unpublished data. The records of the capture of certain rare species are of special importance. The following are notable: Muggiaea delsmani Totton, 1954; Lensia achilles Totton, 1941; Lensia ajax Totton, 1941; Lensia hostile Totton, 1941; Abyla brownia Sears, 1953; Ceratocymba intermedia Sears, 1953; Clausophyes galeata Lens and Riemsdijk, 1908; Sulculeolaria bigelowi (Sears), 1950; Marrus orthocannoides Totton, 1954; Dromalia alexandri Bigelow, 1911. Three newly described species are also included: Vogtia kuruae Alvarino, 1967; Sulculeolaria brintoni Alvarino, 1968; Enneagonum searsae Alvarino, 1968. The isotherms at a depth of 200 meters are used for comparison with the distributional ranges of the species because the position of certain 200 meter isotherms tends to agree with the limits of the ranges. Temperatures are relatively conservative at and below 200 meters, as compared with those in and above the thermocline. It is to be expected, therefore, that general aspects of the ocean climate which existed during the 15-year sampling period are reflected by the distribution of temperature at levels below the thermocline. It is not expected that a particular temperature, perhaps at a particular depth, is associated with a complex of environmental factors that affects or controls the distributional limits of the species.