Effect of tilapia cage culture on algae and cyanobacteria communities in the bays of Bukavu basin, Lake Kivu, DR Congo

Algae and cyanobacteria communities were monitored and associated with nutrients and anthropogenic activities in bays of the Bukavu basin of Lake Kivu (DR Congo). The monitoring was done to investigate the impact of Nile tilapia (Oreochromis niloticus) cage culture on algae and cyanobacteria communities in selected bays. Sampling was carried out from February to September 2021. In all selected bays, a standard quantity of water was filtered through a 10 µm mesh phytoplankton net for planktonic algae, while the epiphytic algae were scraped from cage net walls and macrophytes accordingly. The results revealed higher abundance of pollution-tolerant algae (diatoms) and cyanobacteria in the pilot bays than in the control bay, suggesting impacts of tilapia cages on the aquatic communities. The study detected a significant difference (p ≤ 0.05) in algal and cyanobacteria composition between the pilot and control bays; this could be associated with differences in fish cage and anthropogenic activities around the sampling sites. The study clearly highlighted the influence of nutrient inputs into the development of algae and cyanobacteria communities in the pilot bays, emphasizing the impact of both tilapia cage culture and anthropogenic activities on the alteration of water quality. Therefore, the study recommends relocation of the tilapia cages to bays that are not impacted or less impacted by anthropogenic activities, and to regulation of feed supply. Analyses should be done to elucidate ecological and nutritional importance of the algae and cyanobacteria communities for the development of tilapia cage culture in Lake Kivu.