Parmales (Bolidophyceae) Assemblages In The Subarctic Pacific Ocean During The Mid-1960s

A large collection of old membrane filters from the American cruises of the R/V Vema and R/V Robert D. Conrad has been recently curated and provides a unique opportunity to study microplankton distribution in the 1960s. Filters from the subarctic Pacific Ocean and Bering Sea collected in May-July 1964 and June-Aug 1966 were observed in detail for the first time using scanning electron microscopy, to investigate assemblages of Parmales (Bolidophyceae). These filters were dominated by Triparma columacea f. convexa and T. strigata, with maximum absolute abundances of total Parmales up to 11.0 x 10(3) cells ml(-1) and average abundances often one or two orders of magnitude higher than those of more modern studies. In later studies, Tetraparma pelagica is often cited as the dominant taxon, but it was less important in the 1960s. Since temperature is an important factor in controlling Parmales growth, this shift from high to low absolute abundance, and from the dominance of T. columacea f. convexa/T. strigata to Te. pelagica, could be related to a major climate shift in the late 1970s, and to the dramatic decrease in sea-ice cover and changes in plankton composition in the subarctic Pacific Ocean and Bering Sea.