| Virginia
Journal of Science.
2002. Vol 53 (1) : 13-33 |
| Autotrophic
Picoplankton: Their Presence and Significance In Marine and Freshwater
Ecosystems Harold G. Marshall, Department of Biological Sciences, Old Dominion University, Norfolk, Virginia, 23529-0266, U.S.A. During the first half of the 20th century, scientists collecting plankton specimens would use nets having different sized apertures to selectively obtain organisms within various plankton categories. As these net apertures were reduced in size, it was realized that there were numerous microscopic cells capable of passing through the smallest openings of these nets (Lohmann, 1911). The presence of these very small cells was later reported at numerous freshwater sites (Rodhe, 1955, Bailey-Watts et al., 1968; Pennak, 1968; Votintsev et al., 1972; Pearl, 1977; etc.) and marine locations (Van Baalin, 1962; Saijo, 1964; Saijo and Takesue, 1965; Reynolds, 1973; Banse, 1974; Berman, 1975; etc.). In this early literature, various terms were used to describe these cells (e.g. ultraplankton, olive green cells, μ-algae, nanoplankton, etc.), but it wasn’t until Sieburth et al. (1978) established a plankton reference classification system based on size, that the term picoplankton began to be used collectively for these microscopic cells. The standard definition of picoplankton refers to cells within the size range of 0.2 to 2.0 microns. This term has since been generally accepted as the category to assign plankton cells that occur singly or within colonies that are within this size range. However, one of the initial concerns in algal studies was the inability to distinguish many of the bacteria, cyanobacteria, and eukaryotes in this category with similar characteristics, and to specifically identify the heterotrophs from autotrophs when limited to standard light microscopy protocols. |