The distribution and diversity of land snails in Shimba Hills National Reserve, Kenya

Abstract

The objective of the study was to investigate the distribution and some ecological aspects of land snails in Shimba Hills National Reserve, Kenya. This study was important because no scientific study on snails has been done in this forest, therefore this study will increase malacological knowledge which will in turn necessitate proper management plan for both ecosystem and the terrestrial snails. Molluscs were sampled using standardized direct search and litter sample methods in plots measuring 1m x1m in the different habitat types. Environmental parameters notably temperature, relative humidity, soil, vegetation were investigated. Soil parameters analysed were soil pH, electro-conductivity, soil calcium and soil texture. For vegetation, sampling was done for trees, shrubs and herbs and the plant species identified. In total, 1,748 snail specimens were recorded during the entire study; yielding 28 species from eight families, with family Streptaxidae having the highest number of species with nine species, followed by Subulinidae with six species. The families Maizaniidae, Pomatiasidae and Endodont~~e had one species each. The most abundant species was Gonaxis quadrilateralis belonging to family Streptaxidae, and comprised 12% of the total specimens recorded. The least abundant species was Morphospecies 2. Comparison of snail metrics in three different seasons showed that the wet season had the highest number of individuals with 703 followed by the dry/wet season with 579 individuals and the least in the dry season (466). There were significant influences of

season on land snail diversity (F (2,407) = 6.324, P <0.05) with the wet season recording the highest diversity. When snail abundance was tested using ANOVA, there were significant differences of land snails due to vegetation types (F (4,407) =56.039, P <0.05). Shannon Weiner diversity levels of land snails were highest in the indigenous forest with 0.984 while the grasslands recorded the least diversity of snails with 0.009. Rainfall and other environmental variables such as litter cover, relative humidity and canopy cover had a positive and significant influence on the snail richness while the temperature significantly affected the abundance and richness. The findings ranked Shimba Hills as the richest coastal forest in terrestrial snails in Kenya; having been compared with studies done in Arabuko Sokoke where 25 species were recorded. These results are 'important in exposing the role the forest plays in conservation of land snails and therefore sound conservation strategies should be put in place to protect the ecosystem.