Original paper
Studies of planktonic bacteria in Lake Valencia, Venezuela
Lewis, Jr.; Frost, Thomas; Morris, Donald
Archiv für Hydrobiologie Volume 106 Number 3 (1986), p. 289 - 305
33 references
published: May 13, 1986
DOI: 10.1127/archiv-hydrobiol/106/1986/289
ArtNo. ESP141010603000, Price: 29.00 €
Abstract
The planktonic bacteria of Lake Valencia, Venezuela, were studied between 1977 and 1981. Total counts done by epifluorescence microscopy showed that approximately two-thirds of the bacterial cells were solitary coccoid forms spanning a size range of 0.07 to 4 µm³/cell. Most of the remaining bacterial cells were rod-shaped. The study also documented the steady presence of smaller numbers of distinctive bacterial morphotypes such as Planctomyces. More than 90 % of the bacteria were unattached to any kind of particulate substrate. In the upper water column, the annual average bacterial abundance was 0.5 x 106 µm³/cc, or about 50 µg/l bacterial carbon. This corresponded to about 3 % of phytoplankton cell carbon over the same interval. Bacterial abundance in the upper and lower water column was essentially uniform as long as the lake was mixing. During the stratification season, however, bacterial abundances in the anoxic deep water declined to very low levels. At irregular intervals, penetration of oxygen into deep water caused by thickening of the mixed layer resulted in increases of bacterial abundance in deep water. In the upper water column, the lowest bacterial abundances occurred after the mixed layer had assumed a stable thickness for an extended interval, and increased whenever the thickness of the mixed layer increased. Tests were made for presence of allelopathic substances during the year 1981. These tests showed that significant suppression of bacterial growth could be accounted for by the presence of allelopathic substances. Allelopathic effects were limited to the stratification season and coincided with periods of decline in bacterial abundance and stable mixed layer thickness. Bacterial abundances are not directly related to phytoplankton abundance, but rather to mixing events, which exercise their effect partially through relationships to allelopathy. Calculations incorporating the rates of phytoplankton metabolism and maximum possible rates of bacterial metabolism demonstrate that the planktonic bacteria of Lake Valencia process a very small fraction of the net primary production. Since primary production is also not efficiently intercepted by zooplankton, sediment bacteria and sediment storage play a very large role in carbon flux of this lake.
Keywords
Lake Valencia • Venezuela • bacteria • plankton • anoxic deep water • zooplankton • carbon