DISTRIBUTION AND TAXONOMY OF MOLLUSCS (MOLLUSCA) IN SOME PARTS OF NORTHERN NIGERIA

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Date
2012-11
Authors
GADZAMA, IBRAHIM MADU KATSALLAH
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Abstract
The distribution and taxonomy of freshwater and terrestrial molluscs was studied for three years in twenty five water bodies of four hydrological areas and different terrestrial habitats in northern Nigeria. This was done to determine the mollusc compositions, assess the factors that influenced their distribution and establish their taxonomic positions. Four sampling stations were selected along a line transect across each water body for collection of aquatic molluscs and the physico-chemical factors measured. A portable Combo Hanna® meter was used to measure pH, electrical conductivity, water temperature and total dissolved solids. The specimens of freshwater and terrestrial molluscs and phytoplanktons collected were identified using standard procedure. Soil pH and calcium were measured using pH meter and Atomic Spectrophotometer respectively. The result of the study showed that a total of 14 species of freshwater molluscs belonging to 9 families occurred in the water bodies. Three of the families, Unionidae, Mutelidae and Etheriidae belong to the class Bivalvia while the other six, Viviparidae, Paludomidae, Thiaridae, Planorbidae, Lymnaeidae and Ampullaridae belong to the class Gastropoda. The family Unionidae was represented by three species of the the genus Anodonta. The viviparids were represented by two species of mud snails of the genus Bellamya. The families Mutelidae, Etheriidae, Paludomidae, Lymnaeidae and Ampullaridae were represented by a single species each. The linear regression analysis showed positive relationships between elevation and temperature, alkalinity, chloride and nitrate, indicating corresponding variations with different elevations. The negative relationship between altitude and pH, hardness and dissolved oxygen signifies that water bodies at higher elevations had lower values for these environmental variables. Simpson’s Diversity Index (D) showed Kainji Lake to have the highest diversity (D = 0.88). The algal divisions Chlorophyta, Bacillariophyta, Cyanophyta and Euglenophyta were found to be associated with aquatic molluscs. 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. Soil calcium and pH appeared to be important factors in the distribution of terrestrial molluscs and were positively correlated (P < 0.01; r = 0.93). The widely distributed freshwater species namely; Anodonta marginata and Bellamya crawshayi and the Melanoides species may be termed euryoecious species, having a wide range of tolerance for environmental factors prevailing in northern Nigeria. Species such as Aspatheria sp. and Etheria elliptica were restricted in their distribution due high niche specialization. The Canonical Correspondence Analysis (CCA) showed that temperature, pH, dissolved oxygen, alkalinity, hardness, phosphate phosphorus and sulphate were the likely important factors that significantly influenced the distribution of freshwater molluscs. The patchy distribution of some of the terrestrial mollusc species could have been influenced by the level of rainfall and moisture retention of such areas. The presence of empty shells of freshwater and terrestrial molluscs is an indication of habitat loss due to environmental degradation (desert encroachment and water pollution from anthropogenic activities) which may prolong the aestivation period and result in the eventual death of the molluscs. The intense human activity associated with the water bodies could also have negative impact on the aquatic ecology of the study area. Therefore, habitat deterioration and loss due to human activities are probably the most serious threats to the well-being of molluscs in northern Nigeria. This study has shown that the inland aquatic and terrestrial ecosystems in northern Nigeria support a highly diversified malacofauna of ecological interest and public health significance. There is the need for information data bank to document information on molluscs of northern Nigeria. Proper conservation initiatives should be channelled towards reducing loss of mollusc habitations. The ecological roles of molluscs and the economic gains that can be achieved in utilizing mollusc resources should be appraised.
Description
A DISSERTATION SUBMITTED TO THE SCHOOL OF POSTGRADUATE STUDIES, AHMADU BELLO UNIVERSITY, ZARIA IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE AWARD OF DOCTOR OF PHILOSOPHY (Ph.D) IN ZOOLOGY DEPARTMENT OF BIOLOGICAL SCIENCES, AHMADU BELLO UNIVERSITY ZARIA, NIGERIA NOVEMBER 2012
Keywords
DISTRIBUTION,, TAXONOMY,, MOLLUSCS,, PARTS OF NORTHERN NIGERIA
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