Effects of seasonal dynamics on cyanobacteria proliferation in aquaculture fish ponds

Abstract

Aquaculture production supports the United Nations Sustainable Development Goals (SDGs), especially SDG 2 (Zero Hunger), by enhancing food security and sustainable practices. This study investigated the seasonal dynamics of cyanobacterial (CB) blooms in aquaculture fish ponds in South Africa (SA) and Nigeria (NGA). Water samples were collected twice per season for 1 year and analyzed for physicochemical (temperature, pH, and nutrients), biological (chlorophyll-a and cyanobacteria biomass), and meteorological parameters. FlowCAM analysis revealed Microcystis sp. as the dominant cyanobacterium across all seasons and locations. Cyanobacteria biomass peaked during dry and wet seasons in NGA, with strong positive correlations with nitrate ($r = 0.87$) and phosphate ($r = 0.82$). In contrast, SA fish ponds showed lower cyanobacteria biomass, which was not significantly correlated with temperature or rainfall. Principal component analysis (PCA) revealed that chlorophyll-a and temperature were key drivers in SA, while nutrients were more influential in NGA. The study concludes that nutrient dynamics and aquaculture management practices, rather than seasonal temperature or precipitation, are the primary factors driving CB blooms in tropical fish ponds. NGA fish ponds experienced sustained dominance of Microcystis blooms, driven by elevated nutrient inputs from intensive fertilization and high stocking densities. Hydrological flushing and rainfall-induced dilution offer potential for CB bloom control, though their effectiveness is influenced by local management practices. Keywords: CyanoHABs; fishpond management; Microcystis; seasonal dynamics; sustainable aquaculture