Mangaluru: River Phalguni , which hosted the first-of-its-kind river festival in the coast city recently, has witnessed an interesting phenomena over the last few days.Jellyfish, a saltwater species otherwise found in seas, have swum their way into the river. According to scientists, increased salinity in the river and a rise in temperature are the primary reasons behind the development.Ganesh K, deputy director of College of Fisheries (Mangaluru), told TOI that the construction of Maravoor vented dam has prevented fresh water from flowing into the river. Water is being supplied to 14 villages from the Maravoor dam , a project launched in April 2017. Incidentally, this is the first vented dam under the state government’s Multi-Village Drinking Water Scheme to become operational in Dakshina Kannada. Ganesh said the other reason is the increase in temperature, leading to increased salinity.Prathibha Rohit, senior scientist at the city-based Central Marine Fisheries Research Institute (CMFRI), attributed the influx of seawater during high tides into the river as another reason for the increased salinity. “It is because of saline water in the river, where the water is ideally fresh, that has provided a favourable habitat for the fishes. Also, as summer approaches, salinity of water increases, and the jellyfishes begin breeding. We can expect these jellyfish to be present in the river till February-end,” she said.According to researchers, two variants of jellyfish have been found in the river. Though these do not cause much harm to humans — their bite may cause blisters — they certainly are a threat to other fish species as they feed on the fingerlings of the latter. They also pose a tough competition to freshwater species for space and oxygen.Release of industrial effluents and the dumping of varieties of waste into the river by locals have further suppressed the supply of oxygen, the researchers added.

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