bloom in sufficient density to reflect light strongly back into the sky, and appear in
satellite images as creamy outlines of eddies (Fig. 2.4).
Fig. 2.4 Advanced very high-resolution radiometer (AVHRR) image of the visible
reflections from an Emiliana huxleyi bloom in the Atlantic Ocean south of Iceland.
Lighter colors are from higher reflectance from the plaques of calcite (coccoliths) on
the cell surfaces.
(Courtesy of Steve Groom, Plymouth Marine Laboratory, similar to fig. 2 in Robertson et al. 1994.)
Their cousins, the Pavlovales, retain the full function of a structure between the two
flagellae called a haptonema, constructed of three concentric sheaths of membrane
surrounding a core of seven microtubules. The outer sheath may bear small scales.
The haptonema can bend and coil through activity of the microtubules, allowing it to
serve as a feeding organelle (Kawachi et al. 1991). Particles adhere to it, are moved to
the base, stuck together into a mass, and then moved back out to the tip. The tip then
twists around to the base of the cell, and the surface of the cell forms a food vacuole
around it (phagocytosis). Mixing of autotrophy and phagotrophy is quite widespread,
even in extremely small cells.
Diatoms – Bacillariophyceae
(^) In nutrient-rich coastal waters and during oceanic spring blooms, diatoms usually
dominate the phytoplankton. They range in size from the 2.0 mm Ethmodiscus rex of
the warm, mid-ocean gyres down to about 2 μm, as for example Nitzschia
cylindroformis common in the subarctic Pacific. Diatoms can divide more rapidly