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D. denticulatum is limited at the lower end of its temperature range by temperature values of about 14° to 15°C. In the Pacific it inhabits the subtropical anticyclonic gyres and the area between them. It is carried southeastward past California and Baja California and is spread into the California Current system by horizontal mixing. It survives where the water carries it if temperatures are suitable. The seasonal movements of the isotherms are so rapid that the organism does not at any time inhabit all favorable areas and it may be overtaken in some months by unfavorable environments. In the period from 1949 through 1955, its seasonal movement was to the north in summer and to the south in winter. Its range of spatial fluctuation was less than that of its critical temperature. In the warmer period beginning in 1957, it has lived closer to the coast in late fall and has been more generally distributed in the cooler part of its range than in the earlier years. It has been carried northward by the winter coastal countercurrents and southward again in late spring with the cold upwelled water. The direction of its seasonal fluctuation has thus been reversed in the warmer years.
Berner et al. (Sat,) studied this question.