Proliferation of enterococci in sargassum can contribute towards sand and water quality impairment

The fecal indicator bacteria (FIB), enterococci, are used to evaluate the safety of beach waters and beach sands. The increasing quantities of the holopelagic macroalgae Sargassum fluitans and Sargassum natans (referring to herein as "sargassum") along beaches that face the tropical Atlantic Ocean have motivated field observational studies suggesting that the levels of enterococci at beaches are influenced by the presence of stranded sargassum at beaches. The objectives of this study were to evaluate whether enterococci multiply in sargassum and to evaluate the impact of sargassum on enterococci levels within underlying sand and rainwater leachates. Results show considerable regrowth of enterococci in sargassum under natural rainfall and sunlight conditions. Levels of enterococci in sargassum were initially at 2.3log₁₀ and increased to 5.3log₁₀ (original units of colony-forming units per gram). By the end of the 70-day study, after an 18-day period of no rainfall, the elevated levels persisted in sargassum at 4.8log₁₀. Enterococci levels in sand and rainwater leachates impacted by sargassum were significantly elevated in comparison to the control which did not have a sargassum layer (p < 0.01). Overall results show that enterococci multiplication was associated with the presence of sargassum, contributing towards impaired sand and water quality. This information is of significance for beach managers when they address the need for sargassum removal when strandings are excessive.