Diversity of macro-invertebrates in Thondamanaru lagoon

Abstract

Macro-invertebrates are considered as effective bio indicator of the aquatic ecosystem. Aim of this study is to documenting the diversity and abundance of macro-invertebrates of Thondamanaru lagoon. Sampling was done fortnightly basis from November 2021 to October 2022 from selected 3 sampling sites in Thondamanaru lagoon (S1- beyond the barrage, in front of Field Work Center; S2- near to the barrage and front of Selva Sannathi Kovil and S3- near to sand bar). Samples were collected from each site by using hand net and scoop. A total of 1222 individuals from 7 arthropod families and 15 mollusc families were identified. Based on their morphological characters, 31 taxa were identified by using standard keys. Among all recorded taxa, Gastropods Cerithidea cingulata (24% - 38%) and Clithon oulalensis (31% - 46%) were the most abundant in all the selected sites in Thondamanaru lagoon from family Potamididae and Neritidae, respectively. Macrobrachium sp. (site S1), Penaeus indicus and Penaeus monodon (site S2) were least abundant (1 %). Occurrence of identified taxa at site S3, Libinia emarginata, Oratosquilla oratoria, Murex trapa, Cernuella virgata and Olivancillaria gibbosa were recorded as the least abundant species (≤ 1% ). Species richness and Simpson Index were showed significant difference (p <0.05) among three sites. According to the Shannon Weiner (H) and Simpson (D) Indices, the highest species diversity was observed in Site 3 (H1.9018, D- 0.2072) followed by Site 2 (H- 1.1434, D- 0.3683) and Site 1 (H-1.3995, D0.2805). The highest abundance of macro-invertebrates was recorded in Site 2 (478) followed by Site 3(466) and Site 1 (278). These results revealed that barrage construction across the Thondamanaru lagoon impact on macro-invertebrate diversity. It is very helpful for the conservation of biodiversity of this lagoon.