Aspects of the Population Dynamics of Periwinkle (Tympanotonus fuscatus) along the Bonny River, Nigeria

Abstract

A two-year data set of Periwinkle (Tympanotonous fuscatus) population from a deforested mangrove area was used to assess its population dynamics. Periwinkle snail samples in one hundred (100) 1 m2 quadrats were collected, each in 2015 and 2016. The summary statistics of the periwinkle population show a mean density of 21 indv/m2 in 2015 and 12 indv/m2 in 2016. The length parameter ranged from 0.9 cm-3.6 cm (mean 2.00±0.33) in 2015 and 1.4 cm-5.1 cm (mean 1.76±0.43) in 2016 while the weight parameter ranged from 1.5 g-5 g (mean 1.50±1.51) and 0.4 g-2.53 g (mean 0.70±0.48). The population density indicated a significant change between 2015 and 2016. The total abundance of periwinkle snails between the years declined by forty (40%) percent, varying from a density of 2090 snails in 2015 to 1192 snails in 2016. The distribution statistics also showed that the likelihood of obtaining seven (7) snails in 2016 collections with 1 m2 quadrats declined by 10%; and 18 and 29 snails by sixty-five (65%) percent. The significant difference in abundance values using the Student’s t variance estimate (p<0.05) was also observed (p<0.05) for the variance estimates of the length and weight categories. In the length category, evidence of significant change was indicated by the decline in obtaining the class interval of 1.2 cm-1.6 cm by ten (10%) percent in 2016 collections. Further evidence of significant change in population characteristic was also observed in the weight parameter where the weight class 3 g to 5.5 g was absent in the 2016 collections. The relationship between length-weight was non-collinear in 2015 year collections with a very low R² = 0.007, indicating that the contribution of shell length to body weight can only be predicted by 0.3%. In contrast, in the 2016 collections, the length-weight relationship returned a value of R² = 0.646971 indicating that the contribution of the shell length to body weight can be predicted by sixty percent (60%). These differences in population characteristics were interpreted as evidence of the snail response to interplay of environmental conditions between the dates of collection which were similar. Harvesting pressure and indiscriminate habitat destruction are noted as extreme drivers that can likely overwhelm the natural balance of ecological factors. Although the influences of habitat conditioning factors were not discussed, evidence of the quantitative variation in the population dynamics is given to direct future research in conservation.