Of course, many species occupy two or three water masses, particularly those with
distributions divided by the tropical belt. Apparently, no subtropical species
distinguishes only east- or west-central water masses as an unsuitable habitat. If an
animal is found in one, then it is found in the other.
Fig. 10.11 (a) Regional extent of water masses defined by consistent temperature–
salinity (TS) diagrams.
(After Sverdrup et al. 1942.)
(b) Envelopes (stippled) of TS diagrams from stations where Euphausia brevis was
collected by Scripps expeditions (Fig. 10.6) in the 1950s, compared to general
envelopes (lines) of TS diagrams associated with North Pacific and South Pacific
central waters.
(After Johnson & Brinton 1963.)