Response of periphyton community to salinity gradient in tropical estuary, Niger Delta

Studies on periphyton of Crinium plants were conducted in the estuary (New Calabar River) of the Niger Delta at 4 different locations during the two major seasons (rainy and dry season). Periphyton samples were collected from an area (of 2 cm by 2 cm) in 3 sets of 3 replicates for biomasses (AFDW-ash free dry weight and chlorophyll a) and for numerical abundance. Physicochemical parameters such as temperature, pH, conductivity, hardness and salinity were also collected from the respective stations. Temperature was considerably uniform but conductivity, hardness and salinity showed increasing graduation in concentration down stream. A total of 110 periphyton species were recorded with diatoms constituting 54% of the occurring species followed by Euglenophyta (21%), Chlorophyta (17%), Cyanophyceae (6%) and Rhodophyta (1.8%). There were strong similarities in the values obtained for species richness, periphyton abundance, and chlorophyll a, AFDW (ash free dry weight) for wet and dry season indicating no seasonal influence. However, the periphyton abundance, chlorophyll a and ash free dry weight distribution suggested strongly influence by the salinity gradient. The values for periphyton abundance ranged from 2621 (±168.5) to 3452.8 (±715.9) indiv. cm⁻². In addition, the combined mean values for chlorophyll a, and ash free dry weight in the system were 8.443 ± 2.51 mg cm⁻² and 0.32 ± 0.07 g cm⁻², respectively.