Diel vertical migration of Cryptomonas and Chromatium in the deep chlorophyll maximum of a eutrophic lake

  • Gervais F
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Abstract

Large populations of the phytoflagellates Cryptomonas rostratiformis,
Cryptomonas phaseolus, Cryplomonas undulata and the phototrophic
bacterium Chromatium cf. okenii have been observed in the oxic/anoxic
boundary layer of the slightly eutrophic, dimictic lake Schlachtensee
during the summer stratification. Vertical distribution of these
populations was studied with the help of a new close-interval sampler
and by in Situ fluorescence measurements with fine spatial (cm to
dm) and temporal (h) resolution on 4 days in 1991, 1994 and 1995.
All populations lived close to the chemo dine but showed a regular
diel vertical migration with daytime ascent and night-time descent
and a low migration amplitude. At least for one species— C. rostratiformis—the
pattern of migration suggests that this behaviour has an endogenous
origin. As a result of diel vertical migration, the population of
C.rostratiformis was spatially separated from the other dominating
populations during daytime. Ultimate cause of diel vertical migration
was a better light supply of all populations. Another probable advantage
was the reduction in grazing pressure, as large percentages of all
populations moved into the anoxic, hydrogen sulphide containing water
layers during night-time.

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Authors

  • Frank Gervais

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