Diversity and endemism of three major freshwater groups in Sri Lanka: Atyidae (Decapoda), Gastropoda and Teleostei

Abstract

Eleven species of atyid shrimps (including ten Caridina species), 30 species of freshwater gastropods (including 12 Paludomus species), and 72 indigenous and endemic fishes (including 32 cyprinids of which 16 are Barbus species) have been recorded from fresh and slightly-brackish waters in Sri Lanka. Of these, six Caridina species, at least 11 gastropods (including 10 Paludomus species) and 30 fishes (including 17 cyprinids of which 9 are Barbus species) are endemic. The diversity and endemism of all three groups in Sri Lanka is greater in lotic than lentic waters, and greater in the Wet Zone than in the Dry Zone. Most of the indigenous aquatic fauna is related to that of southern India, but Southeast Asian and African affinities are present also, especially among the atyids. The hypotheses that have been proposed to account for the affinities of the Sri Lankan fauna are reviewed briefly.

Faunal diversity decreases with increasing elevation. Nine species of atyids, 28 species of gastropods and all but one species of fish are found below 500 m, but only two atyids, six gastropods and seven indigenous fishes are found above 1000 m. Of the endemics, three atyids, four gastropods and 11 fishes — all lotic forms — have restricted ranges. Increasing human modification of their habitats could lead to extinctions.