Plankton buoyancy

Auftriebt m, buoyancy upward thrust lift plankton, -mittel, n. buoying agent swelling agent. 

Figure 3. Schematic of the time vs. depth distribution of floats released at various times during a diel cycle of nocturnal mixing and diurnal stratification in the Labrador Sea [E. D Asaro and G. Dairiki unpublished data as shown in 2]. The heavy line (a composite of three separate float deployments) depicts a possible depth history of a non-motile plankton over the 24 h period. Note that trajectories are terminated once they enter the stable diurnal thermocline since they actually start to ascend due to very slight positive buoyancy of the floats.

Plankton are organisms living primarily in the upper part of the water column and although often capable of some motion, particularly vertical migration in zooplankton, are unable to maintain their overall lateral position and drift with the oceanic currents. Buoyancy aids such as oil bodies are sometimes present. The plankton can be divided into phytoplankton and zooplankton. 

The Centrales are generally planktonic because the discoid structure makes it possible to increase the surface area/volume ratio, and thus to increase buoyancy in fresh or salty water. Pennales are generally benthic because their lengthened structure does not permit this buoyancy. Although diatoms are all unicellular, filamentous colonial forms also exist, the length of which can attain 2 mm. A simplified classification of the marine diatoms is presented in Table 9.1 (the main genera for which research into their metabolites has been conducted are shown in bold type). 

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