Abstract:
The world is in the midst of a biodiversity crisis. Now the rate of species extinction is faster than ever before. Many
reasons are responsible for this extinction including human impacts. Among major taxonomic groups that
recorded extinctions, upto 42% are molluscs. Molluscs are one of the most diverse and dominant animal groups
among macro-invertebrates. As they are ecologically and economically significant group, it is important to identify
threats affect on their distribution. The current study was conducted to determine the effect on human impacts on
the distribution of molluscan groups in selected areas of Lunuwila Ela, Galle. The study was continued up to six
months from January to June 2007. Both temporal and spatial data were recorded to determine the human impact
on the distribution of molluscs. A constructed anicut across the stream was considered as a barrier and water
quality parameters and molluscan community structure was studied on both sides of the anicut. Among nine water
quality parameters studied, five parameters showed significant differences between two sides. Salinity levels
indicated the highest variation between two sides (19.08 ppt in site B - 26.07 ppt in site A) and the lowest variation
indicated by Alkalinity levels (6.5 p molL’1 in site B - 9.2 p molL"' in site A). Five molluscan genera (Faunus, Gangetia,
Thiaria, Neritina and Ostria) and one unidentified genus were recorded from both sides of the anicut. Among them
five genera were identified from the upper side and three genera were identified from the lower side of the stream.
Community structure parameters showed that there is a significant difference between two sides of the anicut of
the molluscan community in this stream
