Ae. Detmer et al., PHOTOTROPHIC AND HETEROTROPHIC PICO-PLANKTON AND NANOPLANKTON IN ANOXIC DEPTHS OF THE CENTRAL BALTIC SEA, Marine ecology. Progress series, 99(1-2), 1993, pp. 197-203
An unexpected increase of phototrophic and heterotrophic pico- and nan
oplankton under anoxic conditions was encountered in the central Balti
c Sea below 120 m depth in August 1991 and 135 m depth in July 1992, r
espectively. Cell abundances in anoxic layers were up to 10 times high
er for chroococcoid cyanobacteria, 6 to 8 times for phototrophic nanof
lagellates and 3 to 4 times for bacteria, as compared to the overlayin
g aphotic oxic layers. A characteristic ciliate community occurred at
the oxic/anoxic interface. Phototrophic organisms of anoxic depths wer
e capable of productivity when reoxygenated and returned into the ligh
t. Considerable grazing on bacteria (0.41 to 0.65 d-1) and chroococcoi
d cyanobacteria (1.19 to 1.29 d-1) was revealed by serial dilution exp
eriments. Cyanobacteria showed gross growth rates of 0.85 to 1.33 d-1
under aphotic/anoxic conditions. The origin of deep-water phototrophic
pico- and nanoplankton and the existence of a permanent anaerobic mic
robial food web are discussed.