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Siphonophores are pan‐oceanic; they are found from the equator to the polar oceans in all the major ocean basins. Mackie et al. (1987) concluded that siphonophore distributions coincide reasonably well with the biomes and provinces described in the biogeography literature (e.g. Briggs 1995; Longhurst 1998), which in turn coincide with the earth’s major climatic zones. The best data describing faunal relationships with latitude and longitude come from Atlantic waters. Margulis (1976) recognized seven faunal groups among the siphonophores of the Atlantic, which correspond well to the latitudinal zones of Briggs (Figure 3.36): Arctic species, Northern Boreal species (cf. cold temperate), Antarctic species, Bipolar species (found in the Arctic and Antarctic), Tropical species (which include equatorial and warm temperate components), Eurybiotic species (those which live in all biogeographic areas), and Neritic species. An excellent compendium of Atlantic species’ latitudinal ranges may be found in Pugh (1999). Most (60 of 96 species) were very wide‐ranging, with distributions encompassing 80° of latitude or more, roughly half on each side of the equator.

Mackie et al. (1987) provide a summary of diversity and numbers for 21 common species of calycophoran siphonophores in the North Atlantic. The data show a peak in both numbers and diversity at about 18 °N with a gradual decline in species numbers further north. A second peak in abundance is obvious between 40 and 53 °N.