Aquaculture plume in Red Sea. Water quality, seasonality and trajectory of an aquaculture-associated plume in the Red Sea

We examined the characteristics of the wastewater (estimated 42-48 m3s-1) from a land-based aquaculture facility in the Red Sea, discharged near a spring whale shark aggregation reef. The area around the aquaculture outfall was surveyed using an AUV, echosounder, and profiling package to characterize the biogeochemical properties of the plume and its spatial distribution. The discharge had elevated salinity, density, and turbidity, and formed a dense layer 1-3 m thick above the seafloor. The plume travelled along paths determined by the bathymetry, potentially creating areas with higher residence times. Total nitrogen concentration was over four times higher than surface waters 1.4 km away from the outfall. Estimated daily fluxes of nutrients were 109-123 kg for nitrate-N, 72-82 kg for nitrite-N, 121-138 kg for phosphate-P, and 882-999 kg for silica-Si. Bacteria and cyanobacteria analysis revealed significantly different microbial communities, higher cell counts, and higher relative abundance of genus Arcobacter, a genus associated with opportunistic pathogenic species (e.g., Arcobacter butzleri), while Prochlorococcus sp. was significantly less abundant at the outfall. The effluent was observed 3.8 km from the outfall throughout the year, but even further during late summer and autumn (8.2 km from the outfall).