Biofilm Community Dynamics on Submerged Surfaces in the Lagos Lagoon: Response to Organic Pollution Gradients

Biofilm communities colonising submerged surfaces integrate environmental signals over time and represent sensitive indicators of organic pollution in coastal lagoon systems. This study investigated the temporal dynamics and structural response of biofilm communities on standardised artificial substrates deployed across an organic pollution gradient in Lagos Lagoon, South West Nigeria. Polyvinyl chloride plates were deployed at five stations for 14-day colonisation periods and collected at 7, 14, 28, and 56-day intervals over six months. Biofilm characterised by chlorophyll-a as algal biomass, bacterial cell density, extracellular polymeric substance content, and community diversity based on 16S rRNA and 18S rRNA metabarcoding were assessed. Physicochemical gradient characterisation confirmed elevated biochemical oxygen demand and ammonia at urban stations. Biofilm total biomass accumulated faster and reached higher plateau values at organically enriched stations. Alpha diversity of bacterial and microalgal communities was highest at intermediate enrichment stations and lowest at the most polluted sites, consistent with the intermediate disturbance hypothesis. Proteobacteria and Bacteroidetes dominated bacterial assemblages at polluted sites. Diatom genera including Nitzschia and Navicula were abundant at polluted sites, while Bacillaria and Amphora dominated cleaner stations. Community succession analysis revealed compressed successional trajectories at polluted stations, with early-stage pollution-tolerant assemblages persisting beyond the normal successional timeline. Beta diversity ordination clearly separated communities across the pollution gradient. The study validates biofilm metabarcoding as a rapid ecological assessment tool for urban estuarine systems. Keywords: biofilm, pollution gradient, Lagos Lagoon, metabarcoding, community succession.