Composition and distribution of terrestrial molluscs in relation to soil calcium and pH levels in parts of northern Nigeria

Abstract

The composition and distribution of terrestrial molluscs was studied for three years in different terrestrial habitats in northern Nigeria. This was done to determine the terrestrial mollusk fauna, establish their taxonomic positions and assess the relationships of soil calcium and pH to their distribution. Area sampling technique was employed using a small-scaled grid map of northern Nigeria. Possible collection sites were determined on the basis of on-the-spot-assessment of the potential sample areas. Molluscs were collected over a period of three years, during the wet and dry seasons. The molluscs collected were identified using standard taxonomic guides. Soil samples were analyzed for calcium and pH. A total of twelve (12) species of terrestrial molluscs belonging to six (6) families were recorded. The family Achatinidae occurred throughout the area of study. Only one family of slugs (Veronicellidae) was recorded. Five (5) of the six (6) families were represented by a single species each. The soil calcium content of the sites of molluscs collection averaged at 1.98 0.31 Cmol/kg and the median value (50th percentile) for soil pH is at 6.57. These soil factors were positively correlated (p<0.01; r = 0.93). Terrestrial snails showed preference for soil calcium level of 1.75 to 2.00 Cmol/kg and pH levels between 6.25 and 6.50 and 7.0 to 7.25. The terrestrial ecosystems in northern Nigeria support a highly diversified malacofauna of ecological and probably of public health significance. Aside the level of precipitation and moisture retention of areas of occurrence, soil calcium and pH appeared to be important factors in the distribution of terrestrial molluscs.

Keywords: Terrestrial mollusks; soil calcium; pH; northern Nigeria