Environmental Engineering Reference
In-Depth Information
Table 6.17
Linear relationship between seasonal values
of Shannon-Wiener diversity index and physicochemical
parameters
with zooplankton birth rates and mortality in
laboratory experiments (Wolfi nbarger
1999
).
Rotifers are able to reproduce over a wide tem-
perature range, providing that other factors are
not limiting. It is, however, diffi cult to determine the
effect of temperature on an individual or popula-
tion, as temperature infl uences other processes
which in turn affect the rotifers. Additionally, the
rate of biological processes is seldom infl uenced
by temperature alone but also by a number of other
factors too. It is nearly impossible to separate the
direct and indirect effects of the environmental
factor of temperature (Galkovskaja
1987
).
Berzins and Pejler (
1989
) designated some
species, which peaked during the winter months
as “winter species” and those that peaked in
summer as “summer species.” However, they
opined that the range of occurrence is often so
wide that it is diffi cult to designate these as
“warm-stenothermal species.” Pejler (
1957
)
suggested that genetic differences could be
suspected between populations and geographic
areas, where
Anuraeopsis fi ssa
and
Pompholyx
sulcata
, for instance, otherwise known as pro-
nounced summer forms, were only found at
comparatively low temperatures in northern
Swedish Lapland. Berzins and Pejler (
1989
)
found that many non-planktonic species had their
peaks at comparatively high temperatures, and
this could be because most of them could be peri-
phytic and dependent on macrophytes and their
epiphytic fl ora, which develops during summer.
Persuad and Williamson (
2005
) have observed
that changes in underwater UV and temperature
can signifi cantly infl uence the composition of the
zooplankton community and ultimately food web
dynamics. Thus, it can be that temperature does
not solely decide when and where a species will
occur. Its infl uence is mainly indirect, enhancing
or retarding development and cooperating with
other biotic and abiotic factors.
Another environmental factor that could
affect the composition of rotifer community is
the pH of water in which they live. According to
Hofmann (
1977
), little is known about its influence
on population dynamics of rotifers. However,
according to Edmondson (
1944
) and Skadowsky
(
1923
), pH plays a major role in the distribution
Correlation
coeffi cient (
r
)
Slope (
b
)
Temperature
0.237
0.0334
pH
−0.784**
−1.4066
Dissolved oxygen
0.456
0.1606
Total suspended solids
−0.328
−0.0016
Chlorophyll-a
0.903**
0.0159
Biological oxygen demand
−0.646*
−0.0048
Nitrate nitrogen
−0.300
−0.7375
Total relative phosphate
−0.800**
−0.7214
*
p
≤
0.05; **
p
≤
0.001
rotifers. Various physicochemical factors have
been studied to fi nd the changes, if any, caused by
these factors on the rotifer community.
Temperature is one such factor, which is
often considered to be the most important, in
determining the population dynamics of rotifers
(Ruttner- Kolisko
1975
; Hofmann
1977
). In the
present study, it was observed that rotifers
were maximum in the post-monsoon season
when the temperature was between 24.8 and
25.8 °C. However, when the water temperature
increased in summer, in the range of 26.9-27.5 °C,
a decrease in the rotifer population was observed.
In winter and also when the water temperatures fell
drastically, a subsequent decrease in the rotifer
population was observed. It may be believed that
the rotifers need an optimum temperature for
survival, and when the temperature varies from
the optimum, the rotifer population decreases
drastically. Pejler (
1977
), Dumont (
1983
), and
De Ridder (
1984
), however, stated that most
species of planktonic rotifers have a global distri-
bution and are characterized by wide temperature
tolerances, most of them occurring from close
to zero up to about 20 °C or more (Berzins and
Pejler
1989
). The effects of temperature on
zooplankton populations are often linked with
biotic effects such as increase in fi lamentous
cyanophytes or predators (Threlkeld
1987
).
More direct mechanisms include temperature
sensitivity of metabolism or life history charac-
teristics (Hebert
1978
; Taylor and Mahoney
1988
).
Temperature has also been positively correlated
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