No abstract

Abstract. The ratio of 37-carbon diunsaturated to diunsaturated and triunsaturated alkenones (uK'37) produced by some haptophytes is widely used as a proxy for past sea surface temperatures. However, our isothermal culturing experiments with Erniliania huxleyi clone CCMP372 show uK'37 values to also vary with nutrient availability and cell division rate. These results provide a reasonable explanation for large isothermal variation in uK'37 values of single coccolithophorid strains grown in culture. They also suggest that alkenone-based estimates of past sea surface temperatures may have been influenced by dissolved nutrient concentrations as well as by temperature.

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.

No abstract

Observations of a marked cessation of feeding in filter feeding animals maintained in flowing Narragansett Bay seawater in June 1985 drew our attention to a bloom of a golden alga 2 μm in diameter at unprecedented populations of 109 cells. L−1. This picoplankter lacked morphological features useful in discriminating it from other similar sized forms with either phase contrast or epifluorescence 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 an 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 an 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 Nägeli, 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.