Algae are the naturally produced food for fish in any aquatic ecosystem and an indicator of a productive pond. However, excess abundance of harmful algae can have detrimental effects on fish health. In this study, the algal communities of 30 coastal homestead fish ponds were investigated to identify the diversity, assemblage and controlling environmental variables of harmful algae from a tropical coastal area. The findings showed that 81 of the 89 genera of identified algae were harmful, with the majority of them being in the classes of Cyanophyceae (50.81%), Chlorophyceae (23.75%), Bacillariophyceae (9.5%), and Euglenophyceae (8.47%). Microcystis spp. alone contributed 28.24% to the total abundance of harmful algae. Significant differences (p < 0.05) in algal abundance were found among the ponds with the highest abundance (470 ± 141.74 × 10³ cells L⁻¹) at pond (S₂₅) near agricultural fields and the lowest abundance (109.33 ± 46.91 × 10³ cells L⁻¹) at pond (S₁₄) which was lacking sufficient sunlight and nutrients. Diversity indices, e.g., dominance (D), evenness (J′), richness (d) and Shannon diversity index (H′) ranged from 0.17 to 0.44, 0.23 to 0.6, 0.35 to 2.23 and 0.7 to 1.79, respectively, indicating a moderate range of diversity and community stability. Community composition analysis showed the assemblage was dominated by Cyanophyceae, Chlorophyceae and Bacillariophyceae, whereas, multivariate cluster analyses (CA) identified 11 major clusters. To identify the factors controlling their distribution or community assemblages, eight environmental variables (temperature, pH, dissolved oxygen (DO), salinity, transparency, nitrates, phosphates and sulphate) were measured. ANOVA analysis showed that the variables significantly differed (p < 0.05) among the ponds, and canonical correspondence analysis (CCA) demonstrated that DO, nitrates, phosphates, sulphates, salinity and transparency have the most impact on the abundance of algal genera. In addition, analyses with Pearson’s correlation coefficient showed that the abundance of total algae, diversity and community were mainly governed by phosphates and sulphates. These results can be used to identify and control these toxic algal groups in the local aquaculture sector.

Homestead ponds are small seasonal ponds that are rarely utilized for fish farming. Culturing fish in these small ponds can boost household fish consumption and cash inflow. The availability of nutrients in the water and sediment, however, plays a significant role in the pond’s natural productivity. This study was conducted to assess nutrient contents and some key physical parameters in the bottom sediments of 30 homestead ponds from the central coast along the Northern Bay of Bengal. Analyses of results showed the average values (±SD) of temperature, pH, electrical conductivity, organic matter (OM), organic carbon (°C), nitrogen (N), phosphorus (P) and sulphur (S) were 17.8 ± 1.12 °C, 7.29 ± 0.11, 0.41 ± 0.09 mS/cm, 29,615.48 ± 10,528.9 mg kg⁻¹, 11,958 ± 6107 mg kg⁻¹, 1030.6 ± 252 mg kg⁻¹, 17.1 ± 13.5 mg kg⁻¹ and 32.6 ± 19.7 mg kg⁻¹ during winter and 27.2 ± 1.81 °C, 6.73 ± 0.12, 0.38 ± 0.17 mS/cm, 19,100.01 ± 13,739.07 mg kg⁻¹, 11,079 ± 7969 mg kg⁻¹, 955 ± 229.4 mg kg⁻¹, 26.6 ± 20.2 mg kg⁻¹ and 23.4 ± 15.9 mg kg⁻¹ during pre-monsoon, respectively. One-way ANOVA revealed no significant differences in the mean value of sediment quality parameters among the selected ponds (p > 0.05) except for phosphorus in the winter season (p < 0.05). The sediment quality variables were found to be in the suitable range for fish culture. Pearson’s correlation coefficient values (r) showed that only organic carbon and nitrogen had a strong significant correlation with organic matter (p < 0.05). Based on Cluster Analysis (CA), two major associations among the nutrients were attained at a 15% similarity level: C, OM, and N in one cluster and P and S in another. The findings showed that the parameters were within the preferable range for aquaculture, and the homestead ponds are average productive ponds.