Planktonic organisms can serve as useful bioindicators for monitoring water quality. Certain species of phytoplankton and zooplankton tolerate only a limited range of environmental conditions and can indicate pollution levels. While single species may not reflect every stress, routine biological monitoring provides a reliable and cost-effective approach compared to chemical analyses, and plankton respond rapidly to changes in water quality. Their presence and diversity patterns reflect the integrated effects of various stressors on the aquatic environment over time.

1. PLANKTON INDICATORS
A PROMISING TOOL FOR
MONITORING WATER QUALITY

2. Bio-indicators have provided valuable information for
water resource management in recent years and have
enjoyed increasing popularity.
All species (or species assemblages) tolerate a limited
range of chemical, physical, and biological conditions,
which we can use to evaluate environmental quality.
Planktons that respond rapidly to environmental change
have been very useful and with the identification of
particular indicator species being widely used in
assessing water quality.
Planktons serve as early-warning signals that reflect the
‘health’ status of an aquatic system. Overall routine
monitoring of biological communities is reliable and
relatively inexpensive compared to the cost of assessing
toxicant pollutants.

3. Another benefit of the use of bioindicators is their ability to
indicate indirect biotic effects of pollutants when many physical
or chemical measurements cannot.
The results showed that organisms like Microcystis sp.,
Stigeoclonium sp., Chlamydomonas sp., Oscillatoria sp.,
Frafellaria sp., Navicula cryptocephala, Chlorella vulgaris,
Euglena sp., Closterium sp., Ankistrodesmus falcatus, Anabaena
sp., Gomphonema sp., Nitzschia palea, Synedra ulna, Pandorina
sp., Scenedesmus sp., and Phacus caudate among
phytoplanktons and zooplanktons forms like Brachionus sp.,
Keratella cochlearis, Moina sp., Daphnia sp., Bosmina sp.,
Cyclops sp., Mesocyclopes sp., larvae of Chironomus sp.,
Oxytricha sp., Eristalis tenax, and Epistylis sp. were tolerant to
water pollution.

4. Biological indicators or bioindicators are particular species or
communities which provide information on the surrounding
physical and/or chemical environment by their presence,
absence, frequency and abundance at a particular site. The
basis of each individual species or communities as
bioindicators lies in their preference or tolerance range for
particular habitats and their ability to grow and out-compete
other organisms under particular conditions of water
chemistry.
Certain species have well defined ecological requirements and
their presence and relative abundance in waterways can be
used as an indication of past as well as present water-quality
conditions.

6. Kolenati (1848) observed presence of Trichoptera in Bohemia,
Moravia and the southern part of Silesia, after that attention has
been paid to this type of pollution from the mid-19th century
onwards (Cohn 1853), who observed that biota in polluted
waters were different from those in non-polluted waters.
The first system of rating species as to their sensitivity to lack of
oxygen or a heavy organic load was of Kolkwitz and Marsson
(1908). Nygaard (1949) mentioned that phytoplankton
association could be used as an index of pollution.

7. Bioindicators qualitatively assesses biotic responses to
environmental stress (e.g., presence of the lichen indicates poor
air quality) while biomonitors quantitatively determine a response
(e.g., reductions in lichen chlorophyll content or diversity indicates
the presence and severity of air pollution) (Conti and Cecchetti
2001; Giordiani 2006).
The occurrence of planktonic organisms under natural conditions
is related to tolerance range (ecological optimum) dependent on
abiotic environmental factors (temperature, oxygen concentration,
pH), as well as on the biotic interactions among organisms.

8. In the multidimensional space (ecological niche) the occurrence of
organisms is affected by numerous environmental factors, both
anthropogenic and non-anthropogenic. Bioindicators possess a
moderate tolerance to environmental variability, compared to rare
and ubiquitous species. This tolerance affords them sensitivity to
indicate environmental change, yet endurance to withstand some
variability and reflect the general biotic response (Holt and Miller
2011).
Over time, populations evolve strategies to maximize growth and
reproduction (i.e., fitness) within a specific range of environmental
factors. Outside an individual’s environmental optima, or tolerance
range, its physiology and/or behavior may be negatively affected,
reducing its overall fitness. Reduced fitness can subsequently
disrupt population dynamics and alter the community as a whole.
Bioindicator species effectively indicate the condition of the
environment because of their moderate tolerance to
environmental variability.

9. Good Bioindicator
(i) Species or combination of species must provide measurable response
(sensitive to the disturbance or stress) and the response rapidly reflects
the whole population/community/ecosystem response, when the situation
is even repairable.
(ii) Taxonomically well documented, relatively stable despite moderate climatic
and environmental variability and, life history well understood.
(iii) Easy and cheap to survey and can be reliably identified, using routine
laboratory equipment.
(iv) Indicator should have wide temporal and spatial distribution (rare species
are not optimal), including distribution within area of question. Additionally, it
is beneficial if species already being harvested for other purposes
(economically/ commercially important) and popular in public.

10. Advantages
i) Traditionally conducted chemical assays and directly measured
physical parameters of the water (e.g., ambient temperature,
salinity, nutrients, pollutants, available light and gas levels),
whereas the use of bioindicators reflects overall water quality,
integrating the effects of different stress factors over time.
ii) In addition, contaminants can occur in exceedingly low
concentrations. Tedious analyses with highly sensitive
technologies, at a prohibitive cost, are required to detect such low
concentrations.
iii) Overall routine monitoring of biological communities is reliable
and relatively inexpensive compared to the cost of assessing
toxicant pollutants.
iv) Bioindicators of pollutants are useful in predicting the level and
degree of pollutants (early warning system) before the effects of
the pollutants starts.

11. v) Another benefit of the use of bioindicators is their ability to
indicate indirect biotic effects of pollutants when many physical or
chemical measurements cannot. For instance, phosphorus-
enrichment into a lake will increase the growth and reproduction of
some species.
vi) A common problem with chemical and physical measurements
is that they simplify a complicated response inherent in these
species-rich habitats whereas, bioindicators rely upon the
complicated intricacies of ecosystems and use a representative or
aggregated response to convey a dynamic picture of the condition
of the environment.

12. PHYTOPLANKTON
There are a number of reports that one or more algal assemblage could be
used as organism indicative of water quality.
However, the condition is quiet contradictory under both polluted and
unpolluted water bodies while unpolluted water bodies supports great deal
of algal diversity,
polluted water support just a few tolerant organisms with one or two being
the dominant form.
Palmer (1969) listed ten most tolerant algal species in order of decreasing
tolerance as Euglena viridis> Nitzschia palea> Oscillatoria limosa>
Scenedesmus quadricauda> Oscillatoria tenuis> Stigeoclonium tenue>
Synedra ulna> Ankistrodesmus falcatus> Pandorina morum> Oscillatoria
chlorina with their tolerance (pollution index) as 6,5,4,4,4,3,3,3,3,2
respectively. Pollution index of less than 10 signifies lack of nutrient
enrichment.

13. ZOOPLANKTON
Zooplanktons are minute aquatic organisms that are non-
motile or are very weak swimmers. Although zooplankton
do not depend directly on nutrients to survive, and are
affected by the quantity and quality of algae, bacteria and
detritus in a reservoir, its trophic state may influence the
richness, structure, body size and productivity of this
community.
They play important role in food web by linking primary
producers and higher trophic levels. In oligotrophic
environments with higher water transparency, lower
nutrient concentrations and electrical conductivity, the
nano-phytoplankton is the dominant fraction, allowing high
abundances of herbivorous zooplankton (i.e. filterfeeders
such as calanoids and large cladocerans (Xu et al. 2001).

14. Whereas in eutrophic environments, with higher concentrations
of detritus and nutrients, allow increased growth of bacteria and
protozoa, important food sources for small filter-feeders such as
rotifers and small-bodied cladocerans (bosminids).
Moreover, the predominance of colonial and filamentous
cyanobacteria favors cyclopoids, whose raptorial habit makes it
possible. to feed on these algae, and uses micro-zooplankton as a
food source (Brito, 2011).

15. LIMITATIONS
1. Populations of indicator species may be influenced by factors
other than the disturbance or stress (e.g., disease, parasitism,
competition, predation), complicating our picture of the causal
mechanisms of change.
2. No single species can adequately indicate every type of
disturbance or stress in all environments.
3. Depending upon the specific environment, the species present,
and local disturbances, appropriate bioindicator species or
groups of species need to be selected.

16. CONCLUSION
Planktonic indicators can, and should be used as
complementary techniques in assessing health status of water
bodies.