Why are there about 5000 species of phytoplankton in the sea?

Abstract

The relative abundances of phytoplankton taxa conform approximately to a finite geometric series in which there are 20–25 species per decade of ranked abundance. Such series can contain 160–400 species between the commonest (1022–1026 cells) and the rarest (1010–1014 cells). Thus, between 12 and 31 such series are needed to explain the observed diversity, ∼5×103 species, of marine phytoplankton. The number of series is similar to the number (20–25) of upper-ocean water masses defined by dilution time scale of order 101–102 years. Interpretations of this coincidence are discussed.