Environmental Engineering Reference
In-Depth Information
Table 3.
Pearson product-moment correlation matrix of microbiological variables within the
Cariaco Basin; oxic layer (
<
250 m), redoxcline (250-450 m) and anoxic layer (
>
450 m). BNP
= bacterial net production and DCA = dark carbon (CO
2
) assimilation. Numbers in parentheses
are minimum number of samples compared (n).
Flagellates
Viruses
BNP
DCA
Prokaryotes
<
250 m
ns
ns
ns
ns
250-450 m
0.44*
ns
ns
ns
>
450 m
ns
ns
ns
ns
(28)
(8)
(19)
(10)
Flagellates
<
250 m
ns
0.62**
ns
250-450 m
0.82*
ns
ns
>
450 m
0.74*
ns
ns
(8)
(16)
(7)
Viruses
<
250 m
ns
ns
250-450 m
0.84*
ns
>
450 m
ns
ns
(7)
(5)
BNP
<
250 m
0.75**
250-450 m
ns
>
450 m
ns
(12)
ns = not significant (p
>
0.05); *=p
<
0.05; **=p
<
0.01)
Phylogenetic analyses (18S rDNA libraries) from the Cariaco redoxcline and
anoxic layer have revealed both novel and familiar anaerobic protistan lineages
[52]. Novel lineages include new clades at the highest taxonomic level, branch-
ing near the base of the eukaryotic evolutionary tree. Several Cariaco phylotypes
have high phylogenetic affinities with well-studied microaerophilic and anaer-
obic ciliates, some of whom host archaean and bacterial symbionts that may
carry out geochemically important reactions (sulfate reduction; methanogene-
sis) [9]. Thus, at least three trophic levels (prokaryotes
→
flagellates
→
ciliates)
appear to thrive in the Cariaco's redoxcline.
Viral lysis is the other potential source of prokaryotic mortality. Most recent
evidence suggests that marine virioplankton communities are primarily com-
prised of bacteriophages [5,11,51]. As elsewhere, VLP in surface waters of the
Cariaco Basin are abundant, sometimes exceeding 6 x 10
10
VLP L
−
1
[57]. Verti-
cal distributions are similar to those of prokaryotes, with peaks near the O
2
/H
2
S
interface (Fig. 4c). However, VLP peaks are typically offset from prokaryote
peaks by one depth interval, consistent with the fact that bacteriophages are
produced at the expense of their prokaryotic hosts. Over the course of 8 cruises,
