ECOMORPHOLOGICAL REGIMES OF THE GASTROPOD, PACHYMELANIA BRYONENSIS (POTAMIDIDAE) IN CROSS RIVER, NIGERIARICHARD P. KING AND BASSEY E. AKPAN
Aspects of morphological and ecological patterns in the tidal freshwater gastropod molluse, Pachymelania bryonensis (Wood, 1828) were studied in the lower Cross River (eastern Niger Delta), Nigeria. Individual maximum size (shell height, H) was 68 mm while the typical mean population Hmax = 61-64mm H. Shell height - total weight relationship was isometric (exponent b = 3.011) while shell height - flesh weight function was positively allometric (b = 3.748). Monthly trends in b values and two condition indices suggest that spawning occurs in March-May and July. Annual mean density = 506m-2 and biomass = 1,013.6m-2. The relationship between body size and each of the variables~density and biomass, occurred in two stanzas; mean density increased between 9 and 20mm H and decreased in the 21- 41 mm H size group; mean biomass also increased between 9 and 30 mm H but decreased from 30 - 41mm H. Density and biomass were positive correlates of the size richness (number of size groups), a measure of intraspecific morphometric heterogeneity (diversity). Body size is therefore a critical morphometric determinant of the ecophysiology pattern and population abundance dynamics of P. bryonensis.
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