IN-SITU MORPHOLOGY AND OCCURRENCE OF EUCARYOTIC PHOTOTROPHS OF BACTERIAL SIZE IN THE PICOPLANKTON OF ESTUARINE AND OCEANIC WATERS1

Authors


  • 1

    Accepted: 10 February 1982.

  • The research was supported by grants OCE-7681779 and OCE-7826388 from the Biological Oceanography Program of the National Science Foundation. We acknowledge Andy Davis and Jim Fontaine for the collection of water samples and the establishment of enrichment cultures during R/V Endeavor cruises 20 and 28, respectively.

ABSTRACT

Concentrates of the picoplankton (0.2–2.0 μm) sized fraction from the euphotic zone of estuarine and oceanic waters were examined by transmission electron microscopy. In addition to the numerous phototrophic procaryotes (chroococcoid cyanobacteria) previously reported, small phototrophic eucaryotes were observed in 20 of 25 samples examined. Micromonas pusilla (Butcher) Manton and Parks, a 1 × 1.5 μm flagellate, was abundant in estuarine samples in summer. Similar sized cells of non-flagellated chlorophytes, either Nannochloris Naumann or Chlorella Beijerinck, were observed sporadically in many samples. The most ubiquitous microalga was a scaled, non-flagellated prasinophyte that occurred at 9 of 15 different locations on 15 of 20 sampling dates in water samples from Iceland to the Caribbean Sea, This tiny alga (0.5 to 1.0 μm in diam.) is probably the smallest known photo-trophic eucaryote and has not heretofore been described. Enrichment cultures using conventional techniques on several cruises yielded only the Chlorella-type of green alga, as well as numerous isolates of unicellular chroococcoid cyanobacteria.

Ancillary