Abstract:
Biological indicators including macro-invertebrates are more accepted
monitoring tool to assess the aquatic bodies. Thondamanaru lagoon is experiencing
loss of biodiversity in and around the lagoon. This study was conducted for one year
period from November 2021 to October 2022 to analyse the present status of water
quality with macro-invertebrate survey in the upper part of the northern basin of Thon-
damanaru lagoon. Mud and water sample were collected twice a month from follow-
ing three sampling sites: S1- Bayond the barrage, in front of the field work center (N-
9º 81.27ʹ, E- 80º 12.88ʹ) S2- near the barrage and in front of Selva Sannathi Kovil (N-
9º 82.04ʹ, E- 80º 13.11ʹ) and S3- near the sand bar (N-9º 82.04ʹ, E-80º 13.46ʹ). Water
quality parameters including water temperature, salinity, pH, dissolved oxygen, elec-
tric conductivity, oxidation reduction potential, alkalinity and orthophosphate that can
affect the distribution and abundance of macro-invertebrates were assessed. Based on
the morphological characters, among identified 31 taxa, gastropods were the most
abundant group. Fresh water shrimp Macrobranchium sp. was found for the first time
at S1 but no longer exist throughout the period. Based on the statistical analysis by
one way ANOVA, species richness, Simpson index, salinity, pH, total dissolved solid
and electric conductivity showed significant differences among the three sites
(P<0.05). This study revealed the impact of barrage construction across the lagoon on
the diversity, distribution and abundance of macro-invertebrates with extensively
changing the movement of water flow and water quality. Continuous monitoring and
sustainable lagoon ecosystem management are need to maintain the biodiversity and
ecosystem health of Thondamanaru lagoon
