Ultrastructure and Ecology of Aureococcus Anophagefferens Gen. Et Sp. Nov. (Chrysophyceae): The Dominant Picoplankter During a Bloom in Narragansett Bay, Rhode Island, Summer 1985

Abstract

Observations of a marked cessation of feeding in _filter feeding animals maintained injowing Narragansett Bay seawater in June 1985 drew our attention to a bloom of a golden alga 2 pm i n diameter at unprecedented populations of 1 O9 cells. L-I. This picoplankter lacked morphological features useful in discriminating it from other similar sized forms with either phase contrast or epzfEuorescence light microscopy. Natural populations of picoplankton, obtained from the height of the bloom until its decline, were examined in thin section with transmission electron microscopy. A cell with a single chloroplast, nucleus, and mitochondrion and a n unusual exocellular polysaccharide-like layer was apparently the bloom alga. The ultrastructure of this alga is consistent with that of the Chrysophyceae, and a new genus and species, Aureococcus anophagefferens is described.Attempts to grow this previously unrecognized picoplanktonic alga as a n obligate phototroph failed and only yielded cultures of other previously described picoalgae. Facultative and obligate phagotrophic protists with ingested cells of Aureococcus were only observed as the bloom waned and minute diatoms became common. Cells of A. anophagefferens with virus particles typical for picoalgae occurred throughout the bloom. Populations of the usually dominant photosynthetic picoplankter, the cyanobacterium Synechococcus Nageli, were depressed during the bloom. This could be due in part to selective grazing on Synechococcus rather than Aureococcus by elevated populations of Calycomonas ovalis Wulff which accompanied the algal bloom.

Viruses in Marine Planktonic Systems

“…In contrast, Sieburth et al (1988) suggested that even though virus-infected cells were visible throughout a bloom of the small chrysophyte Aureococcus anophagefferens, the bloom declined only after significant numbers of phagotrophic protists developed. They suggested that the viruses primarily influenced the genetic structure of the algal community (species and/or strain composition) rather than its size.…”

“…It was not until the late 1980s that direct counts of viral abundances in the range of 10 ~ mL ' were reported by Sieburth et al (1988) using epifluorescence microscopy to count virus-sized particles stained with a DNA-specific fluorochrome (DAPI), and by Proctor et al (1988) using TEM. These were followed shortly by estimates ranging from <107 to >10 ~ mL ' for a variety of marine waters (Bergh et al, 1989;Proctor and Fuhrman, 1990), including the Gulf Stream and open ocean.…”

“…Sieburth (1979) used TEM to observe viruses in seawater but did not provide concentration estimates. The first quantitative estimates of viral abundance in seawater were provided by Torrella and Morita (1979) who reported >104 viruses mL' in coastal Oregon waters.…”

Growth and photosynthesis of the 'brown tide' microalga Aureococcus anophagefferens in subsaturating constant and fluctuating irradiance

“…The alga was identified and described by Seiburth et al (1988) as the chrysophyte Aureococcus anophagef-ferens gen. et sp. nov.…”

Carbon cycling: Molecular regulation of photosynthetic carbon fixation

“…This alga, named Ostreococcus tauri reached concentrations of 104 to 105 cells/ml. Others have found microeucaryotes to have an increasingly important role in primary production in coastal [22,81,87] and oceanic environments [66].…”