JOIN USOligochaetes are considered as indicators of healthy aquatic ecosystem. But due to damaging practices, they are on a dying curve. Prashanth Hegde throws light on their current state in Karnataka
What can a lichen in a forest tell us about pollution? Well, it can tell you that the forest is free from sulphur dioxide pollution. Similarly, an algal bloom in a lake can be the
indicator of excessive nitrates and phosphates in the water. Bioindicators like these are used in a major fashion in environmental studies all over the world. Many agree upon the fact that looking at such indicator species in the natural habitat bodes well for detecting pollution, especially in air and water.
Bioindicators are essentially, living organisms that can indicate the quality of any ecosystem. They include anything from lichens, mosses, algae species,
bacteria, fungi and macroinvertebrates. These organisms have varied stress
responses to diverse stressful situations and these responses determine the extent of pollution.
Natural agents
One of the major bioindicators are aquatic oligochaetes. These organisms are
microscopic earthworms (Phylum annelida), characterised by a segmented body, clitellum at sexual maturity and hair-like structures called seta that help them in swimming. They help decompose organic matter into inorganic nutrients and play major ecological roles. They are an important food chain component, where they feed on bacteria or algae and become food for fishes. They break down larger soil particles into fine sediments aiding the erosion process. They are of extreme utility and relevance in Ecological Risk Assessment (ERA), which involves pollution monitoring, toxicity testing, and sewage treatment.
They are the most important microinvertebrates and can adapt to every kind of water – salty, brackish or fresh. They thrive in small streams, large rivers, marshes, ponds, lakes, springs and even groundwater. Spread over 1700 species, they are the least studied among the invertebrate fauna due to difficulty in species identification. We still don’t have the complete data set related to the microdile of the wetlands in Karnataka.
The distribution of aquatic oligochaetes depends on habitat specificity such as light penetration, dissolved oxygen, detritus (non-living particulate organic material), planktons, water PH and temperature. Very few species are tolerant to organic or sewage pollution and most of species sustain only in the absence of human
interference. For example, majority of oligochaetes belonging to family Naididae are very sensitive to water pollution. The species Aulophorus furcata, Aulophorus vagus, Allonais paraguayensis multiply rapidly by fission (asexual reproduction) in unpolluted lakes and paddy fields.
Water bodies like lakes and rivers are highly productive and species-rich
habitats. If you collect a litre of water from undisturbed pond in post-monsoon
season, you will find rotting materials with loads of macroalgae and planktons. The aquatic communities like algae, invertebrates, amphibians and fishes will be more abundant in such water bodies. Biological oxygen demand (BOD) does not become noticeable limiting factor in such cases.
But metazoan worms like the Pristina proboscida, Pristina longiseta found in
decaying leaves and water bodies, seem to be tolerant to BOD and organic
pollution. Also, it has been found that the species of Tubifex tubifex (sludge worms) survives in eutrophic lakes (characterised by algal bloom), where BOD is significantly more and pollution potential is high. This species is extensively used as food for fish in aquaculture practices.
Damaging factors
Discharge of sewage, industrial effluents, and water carrying agrochemical wastes, excessive spreading of weed plant on water surface are some of the major
causes of depletion of such wetland species. Also, the changing seasons contribute to the degradation of such wetlands. While some go completely dry in summer, some do regain their water content during the next monsoon. Moreover, anthropogenic factors like extensive fishing goes unregulated in most fresh water bodies of Western Ghats and west coasts.
The lakes of Talaguppa, Sagar, Ananthpur of Shivamogga district and several such lakes of Dakshina Kannada (Anekere at Karkala) and Udupi districts witness human interference, disposal of domestic-solid wastes, and degradation in a major fashion due to lack of conservation efforts. The non-biodegradable solid wastes are being dumped into easily accessible roadside natural wetlands. These threats have a great impact on communities of microdiles and reduce the bioindicators in great numbers.
Conservation and monitoring of the smaller wetland flora and fauna in the Western Ghat should be treated as major issue by forest department. National Wetland Conservation Programme (NWCP), Ramsar Convention on Wetland and Salim Ali Centre for Ornithology and Natural History (SACON) aims at conservation and wise use of wetlands in the country so as to prevent their further degradation. Energy and Wetlands
Research Group, Centre for Ecological Sciences, Indian Institute of Science,
Bengaluru is also focusing on conservation and sustainable management of wetland ecosystems in the vulnerable Western Ghats. But the awareness about wetland conservation seems to be inadequate at the national level. But the support of local public can give a huge boost to the programmes.
The thirteenth International Symposium on Aquatic Oligochaeta, Brno, Czech Republic, held from September 7-11, 2015 (ISAO 2015) is proposed to be the perfect platform for researchers to exchange their findings to realise the significance of these microdiles in the wetland research. In the present scenario of lack of scope in basic science research, the government has to initiate special projects and programmers to conserve the rich wetland flora and fauna of Western Ghats and the west coast of Karnataka.