Environmental Engineering Reference
In-Depth Information
Figure 5.
Vertical distributions of total ciliated protozoan communities relative to first depth
of undetectable O
2
at Station CARIACO on four dates. Scaling factors presented in each panel.
One important question is whether these levels of production are sufficient
to support observed prokaryotic inventories. Specific growth rates calculated
by dividing the sum of dark DIC assimilation and BNP rates by microbial
biomass for the 11 cruises in which all were measured, yields a range of
cell division rates of 0.02 - 3.02 d
−
1
and a median value of 0.38 d
−
1
(
x
=
0.60 d
−
1
; n = 77). Sixty four of 77 observations yield growth rates below 1.0
d
−
1
and only 13% yield rates
>
1.5 d
−
1
. Comparable growth rates (0.07 - 2.3
d
−
1
) have been observed in surface waters of the oligotrophic Sargasso Sea [6].
Therefore, growth rates are not unreasonable for microaerophiles and anaerobes
in productive coastal waters with temperatures consistently
>
17
◦
C. Moreover,
measured prokaryotic production rates (chemoautotrophy + BNP) are sufficient
to support the microbial communities observed in the Cariaco's redoxcline.
On average, chemoautotrophy represents about 70% (median) of local pri-
mary production in surface waters at Station CARIACO (Fig. 8). Similarly high
proportions have been reported previously for the Cariaco Basin and Black Sea
[21,35,56,61]. All existing evidence suggests that this production is fueled by
remineralization of export production from surface waters. However, a semi-
enclosed ecosystem in steady-state can not sustain such high energy recoveries
because less than 10% of local surface production (in C units) sinks to the
