THE VARIED ROLES OF SNAILS - National Universities Commission

cooked. Such wastes contain large granules of oil, acids,
mineral contents, and poisonous wastes all of which also
reduce the snail populations when their levels exceed the
tolerance limit.
(iv) Factors affecting snail populations
Four environmental factors affect snail populations
viz
Water levels.
Current speed
Temperature/shades
Elevation.
(b) Snails as Biological Indicators of Pollution and age
of the environment:
Palaeoecologists have since noted the presence of
gastropod remains in geological sediments and included
these in the interpretation of geological age of past
environment and perturbations (Crisman, 1978). The
shells of gastropods are preserved well and are located
in calcareous sediments. These fossils provide
information regarding water and soil chemistry, lake
trophic state, variations in oxygen distribution and
concentrations over time, and the changes in water
levels following geological times.
Studies show that molluscs generally do not inhabit
strong acidic waters and their shells are rarely preserved
in weakly acidic environments. In freshwaters Okafor
(1990) traced the relationship between humic acids and
snail distribution and abundance and found a highly
negative correlation. In that study, it was observed that
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