S. Vanucci et al., Microbial assemblages associated with sinking particles in the Porcupine Abyssal Plain (NE Atlantic Ocean), PROG OCEAN, 50(1-4), 2001, pp. 105-121
Downward fluxes of microbial assemblages associated with sinking particles
sampled in sediment traps deployed at nominal depths of 1000 m (trap A), 30
00 m (trap B) and 4700 m (trap Q were measured between October 1995 and Aug
ust 1998 on the Porcupine Abyssal Plain (PAP, NE Atlantic). The goal of the
study was to provide detailed information on the microbial contributions t
o the particulate organic carbon and DNA fluxes. Bacterial fluxes associate
d with settling particles in the PAP area were generally low and significan
tly lower than bacteria] fluxes reported from the same area during 1989-90.
Marked seasonal pulses in the microbial assemblages were observed in all y
ears that were associated with particle flux maxima in April-June. No signi
ficant differences were found in microbial fluxes between 1000 and 4700 m d
epth, but both the bacterial biomass flux and the frequency of dividing bac
teria increased with depth, suggesting that organic matter turnover and con
version into bacterial biomass increased in the deeper traps. The structure
of microbial assemblages displayed clear changes with increasing depth;, t
he ratios of bacteria to both flagellates and cyanobacteria increased up to
4-fold between 1000 and 4700 m, showing a marked increase in bacterial dom
inance in the deeper layers of the water column. A parallel increase of the
bacterial contribution to particulate organic carbon (POC) and DNA fluxes
was observed. Total microbial contribution to the POC flux in the PAP area
was about 2%, whereas the contribution of cyanobacteria was negligible. Flu
xes of microbial assemblages were significantly correlated with DNA fluxes
and on average the bacteria accounted for 5% of DNA, fluxes. Data reported
here confirm that the "rain" of particulate bacterial DNA may represent an
important source of nucleotides for deep-sea bacteria, but also suggests th
at a much larger pool of detrital DNA is potentially available to deep-sea
micro-organisms. (C) 2001 Elsevier Science Ltd. All rights reserved.