Coccolithophorids of the North Pacific Central Gyre with notes on their vertical and seasonal distribution

Scanning electron micrographs supplement earlier observations on the living coccolithophorids of the North Pacific Central Gyre, and suggest that new forms may be present among the 44 taxa described. Vertical and seasonal distribution data obtained from 6 cruises during 1972-1974 confirm the existence of depth-dependent communities, particularly in the summer months. The populations become less structured in the winter months when some taxa, notably Emiliania huxleyi, expand their depth range, probably responding to a greater degree of mixing in the water mass. Coccolithophorids of the North Pacific Central Gyre with notes on their vertical and seasonal distribution INTRODUCTION In the course of an inverted microscope study of the total range of microplankton in a 400-sq. mile area of the North Pacific Central Gyre in the region of 28?N, 155?W, the coccolithophorid data proved to be most useful in testing the hypothesis of seasonal stability of populations. It was therefore important to identify as many forms as possible, and the SEM (scanning electron microscope) was used to supplement light microscope analysis. The following illustrations and descriptions resulted from these studies. Illustrations are introduced which further clarify existing taxa and new forms are described, although too few specimens were encountered to allow formal establishment of new taxa. The use of the TEM (transmission electron microscope) for morphological and taxonomic work in this group began in the 1 950's, resulting in papers such as those by Deflandre and Fert (1954) and Halldal and Markali (1955), and has continued to the present with major contributions from Gaarder (1962), Mcintyre and B6 (1967), Kamptner (1967), Gaarder (1970), Gaarder and Hasle (1971) and Okada and Mcintyre (1977). The last 3 include some SEM micrographs, but the publications based mainly on SEM work are those of Martini and Muller (1972), Heimdal (1973), Borsetti and Cati (1972, 1976), Kling (1975) and Gaarder and Heimdal (1977). Earlier, coccolithophorid taxonomists depended on the light microscope and made surprisingly accurate observations, e.g. Lohmann (1902, 1912, 1913b), Schiller (1930), Kamptner (1927, 1941), and Lecal-Schlauder (1951). The taxa illustrated and described herein were selected from a total of 53 named species and a group of unidentified forms found in the light microscope analysis of the gyre samples. Some previously welldescribed species were not included. Table 1 summarizes seasonal and depth distribution data for selected species derived from this analysis but does not include all the forms illustrated here, some of which were not recognized at lower magnifications. For further discussion of the total microplankton of the North Pacific Central Gyre refer to papers presently being prepared by Beers, Reid and E. Stewart and by Beers, Reid and G. Stewart. Data records for 5 cruises are published as IMR Report 75-6 (Beers, Reid and Stewart, 1975) and 77-1 (Beers, Reid and Stewart, 1977). Cato 1 data were incomplete due to sample loss. These records have quantitative data on all microplankton taxa identified, including many of the coccolithophorids described in this paper and notes on name changes that have been made during the years spent on this study. micropaleontology, vol 26, no. 2, pp. 151-176, pls. 1 -9, 1980 151 This content downloaded from 207.46.13.151 on Fri, 25 Mar 2016 07:39:58 UTC All use subject to http://about.jstor.org/terms F. M. H. Reid: Coccolithophorids of the North Pacific Central Gyre TABLE 1 Vertical and seasonal distribution of selected species based on numbers averaged over several stations for each cruise. Cruises arranged seasonally rather than chronologically. "Intermediate" group Lower layer group