The Effects of Sieve Mesh Sizes on Benthic Macrofuana of Azuabie and Obufe Creeks in the Upper Bonny Estuary, Niger Delta

Abstract

An investigation of benthic macrofauna was undertaken in the Azuabie and Obufe Creeks of the upper Bonny Estuary. One aim of the study was to determine the effect of sieve mesh sizes on macrobenthic fauna in the two Creeks. Five and four Stations were chosen in Azuabie and Obufe Creeks respectively and Sediment samples were collected monthly with an Eckman grab from February 2021 to January 2022. Four replicate samples were collected and sieved through 1mm, 0.5mm and 0.35mm sieve mesh sizes. Monthly composite data from each creek was used to determine the effects of sieve mesh size on the composition and abundance of benthic organisms. The data was subjected to Analysis of Variance (ANOVA) and Tukey tests where significant difference was inferred by ANOVA. A total of eighteen (18) species were observed but two (2 species (Obinnia johnsoni and unidentified cumacean) were not retained in the 1.0mm mesh sieve and this is suggestive of exclusion based on size. The 0.35mm sieve retained the highest percentage abundance (88% in Azuabie and 63% in Obufe) of benthic macrofauna followed by 0.5mm (10% in Azubie and 28% in Obufe) and the least being 1.0mm (2% in Azuabie and 9% in Obufe). Also, the 0.35mm and had significantly higher values of mean total abundance than the 0.5mm and 1.0 mm mesh in both Azuabie and Obufe Creeks (ANOVA, p<0.001), with Tukey Tests showing 0.35mm > 0.5mm > 1.0mm in Azuabie and 0.35mm>0.5mm=1.0mm in Obufe. . It is concluded that the 0.35mm mesh sieve is the preferable option for detailed studies of macrobenthos in the Bonny Estuary.

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