Environmental Engineering Reference
In-Depth Information
MICROBIAL ECOLOGY OF THE CARIACO
BASIN'S REDOXCLINE: THE U.S.-VENEZUELA
CARIACO TIMES SERIES PROGRAM
Gordon T. Taylor
1
, Maria Iabichella-Armas
2
, Ramon Varela
3
, Frank M uller-
Karger
4
, Xueju Lin
1
and Mary I. Scranton
1
1
Stony Brook University, Marine Sciences Research Center, Stony Brook NY 11794-5000, USA
2
Universidad de Oriente, Instituto Oceanografico de Venezuela, Cumana, Venezuela
3
Fundaci on la Salle de Ciencias Naturales,
Estacion de Investigaci ones Mari nas de Margarita,
Nueva Esparta, Venezuela
4
University of South Florida, Department of Marine Sciences, 140 7th Avenue South, St. Peters-
burg 33701 USA
Abstract
The cooperative U.S.-Venezuela CARIACO program (
CA
rbon
R
etention
I
n
A
C
olored
O
cean) has begun to elucidate the microbial ecology of the Cariaco
Basin's redoxcline. This anoxic water column supports highly stratified microbial
assemblages of prokaryotes, protozoa and viruses, exhibiting abundance and
activity maxima near the O
2
/H
2
S interface. In the oxic layer, abundance and
activity of microheterotrophs vary annually to the same extent (16 to 20-fold)
as primary producers in the upper 75-100 m, but out of phase. In the redoxcline
and anoxic layer, relationships of these same variables to surface production are
not readily apparent. Heterotrophic carbon demands within the redoxcline exceed
local delivery of sinking organic matter from the mixed layer. The Cariaco's redoxcline
appears to be inhabited by microaerophilic and anaerobic chemoautotrophs,
such as ε-proteobacteria, whose metabolism is controlled by inorganic chemical
gradients and transport. Time series data demonstrate that distribution and activity
profiles of prokaryotes, protozoa and viruses vary in response to one another
and to fluctuations in the interface's position. Rapid turnover of prokaryotic
biomass in the redoxcline is deduced from the perennial presence of bacterivorous
protozoan and viral communities. Chemoautotrophic production is sufficient to
support heterotrophic demand for reduced carbon within the redoxcline and yields
reasonable specific growth rates for total prokaryotic communities, averaging
between 0.4 and 0.6 d
−
1
. However, reconciliation of microbial demand for energy
and oxidants with supply is not possible applying the classic 1-D vertical model
to the Cariaco and remains one of the greatest challenges to understanding the
microbial ecology of anoxic water columns in general.
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