AQUATIC BIODIVERSITY |
Phytoplankton are the primary producers of aquatic ecosystems. They are also one of the rapid detectors of environmental changes because of their quick response to pollutants and fluctuating light and temperature conditions. Pollution stress reduces the algal species diversity but increases the number of individuals of few tolerant species. We studied seven streams as well as the reservoir waters in the upper catchment and ten streams in the lower catchment for phytoplankton. The study area has a rich diversity of 216 species belonging to 59 genera. Of these the diatoms are more common in streams and desmids in the reservoir. No algal blooms indicative of eutrophication was found during the survey. However, it should be taken with caution that all the waters of streams and the reservoir show light to moderate levels of pollution.
Zooplanktons are the secondary producers of the aquatic ecosystems. They transfer energy from primary producers to higher animals and therefore play an important role in the nutrient cycle of these ecosystems. Zooplanktons were studied in thirteen localities. The freshwater zooplankton of the river is rich and diverse. We could record 39 species. The species richness was low in lotic system compared to lentic water system. No large zooplankton was recorded mainly due to predatory pressures from fishes.
Insect groups like Mayflies, Dragonflies and Caddiesflies are important in the functioning of stream ecosystems. They are important links in the nutrient cycling in forest streams. They process wood and leaf litter and degrade them into forms absorbable by fungi and bacteria. These nutrients are absorbed by plants of the riparian zone. Aquatic insects also form food for fishes. During our study covering 12 sites and 20 sampling localities a total of 37 genera belonging to 27 families were collected. Votehalla in the lower Sharavathi catchment with 18 genera topped the streams in insect communities. In streams subjected to higher temperature due to poor canopy cover the generic diversity was low.
For the first time a monotypic genus i.e., Phylloneura westermanni, is recorded in the study area, which was earlier reported from only Nilgiris, Coorg and Wayanad in 1933 by Fraser, from a Myristica swamp of Kathlekan in Siddapur. The presence of Philorus in the Votehalla stream indicates its pristine nature and presence of primeval forests around. Some pollution sensitive genera have also been found in Kathlekan indicating the beginning of human disturbances.
The Western Ghats is renown in the world for the diversity of endemic fishes. A total of 51 species belonging to 32 genera and 16 families has been recorded only from the upper catchment of Sharavathi. From the lower catchment also 51 freshwater fish species have been recorded. The Sharvathi estuary has a total of 44 species of fishes. Altogether, the entire basin has a total of 112 species. The prominent endemic species are Tor khudree, Labeo fimbriatus, Puntius fasciatus, Puntius filamentosus, etc. The investigation in the downstream has reported a new species - Parabatasio sharavatiensis.
The study of locality-wise species distribution revealed that, western streams and reservoir areas were dominated by native and endemic species and absence of introduced exotic species. Compared to this, on the eastern side most of the native species are gradually becoming rare due to insufficient food availability, disease and over exploitation. Epizootic Ulcerative Syndrome (EUS) affected mainly the, Channa spp., catfishes and minor carps. The outbreak of parasitic infection in Mastacembelus armatus (havu meenu) substantiates that the native fishes are continually being affected. The practice of targeting the breeding grounds (for fishing) is a threatening factor to native fish species like Garra, Gonoproktopterus, Puntius, Labeo, Cirrhinus, Mystus, and Pseudeutropius etc. Silt deposition in the reservoir due to poor catchment conditions has damaged the breeding areas of endangered species such as Mahseers.
