Environmental Engineering Reference
In-Depth Information
1986 [31], indicate much higher (by a factor of 5.5) zooplankton counts and
biomass within the oxic mixed layer than in the O
2
depleted subsurface waters.
Despite severe O
2
depletion, total zooplankton biomass (displacement volume)
at this station was quite high (
12 mL m
−
3
). Copepods were the most abundant
group (over 65%) and about 25% of all zooplankton were carnivores. Although
almost all groups were present both above and below the pycnocline, the
larger organisms tended to be concentrated in the surface layer. While the total
biomass varied with the mixed layer thickness, the latter probably modulated
by tidal mixing, there was little evidence for vertical diurnal migration. These
observations indicate that the zooplankton avoid O
2
deficient waters.
∼
9
(a)
8
7
6
12.0
8.4
8
(b)
4
0
10 600
4000
3000
2000
1000
(c)
400
0
0200
0800
1400
2000
0200
0800
1400
Time ( hours )
Figure 9.
Variations in mesozooplankton biomass (b) and density (c) in relation to mixed layer
depth (a) with time at an anchor-station off Goa (15
o
26'N, 73
o
35'E; water depth 32 m; dates of
sampling 28-29/09/1986). Dark and light bars denote values below and within the mixed layer,
respectively (redrawn from Madhupratap et al. [31]).
