Phytoplankton Abundance in relation to Nitrate and Phosphate Dynamics in a Brackish Water Aquaculture Pond System in Marana, Maros Regency, South Sulawesi, Indonesia

Phytoplankton is a primary food source in aquaculture systems, and the size fractions play distinct roles in nutrient cycling. This study aimed to evaluate the relationship between the abundance of size-fractionated phytoplankton and nutrient concentration in brackish water aquaculture systems in Marana Silvofishery, Maros Regency, South Sulawesi, Indonesia. Phytoplankton were categorized into three size fractions (25, 40, and 60µm), and their abundance was quantified alongside nutrient concentrations. Statistical analyses, including one-way ANOVA and Tukey's HSD test, revealed significant spatial variation in phytoplankton abundance and nutrient levels. Correlation and linear regression analyses revealed that phosphate had a stronger influence on larger phytoplankton size fractions (40 and 60µm) despite consistently higher nitrate concentrations. In contrast, smaller fractions (25µm), likely dominated by picophytoplankton, exhibited higher abundance and adaptability, reflecting their efficient nutrient uptake strategies. Environmental conditions were consistent across the stations, ensuring stable growth conditions. Nitrate concentrations were higher than phosphate levels, but phosphate had a stronger influence on the larger phytoplankton size fractions. Smaller fractions were more abundant, reflecting nutrient uptake efficiency. The results enhance the understanding of phytoplankton-nutrient interactions in brackish water ecosystems and contribute to sustainable aquaculture practices. This study provides insights into the ecological dynamics of phytoplankton in brackish water aquaculture systems, showing the need for balanced nutrient management to optimize natural feed availability.