No abstract

Cyanobacterial blooms have increased in coastal waters worldwide, facilitated by excessive nutrient input and apparently global warming. They exert negative consequences in marine ecosystems, communities and habitats. Although reports of these events are frequent, their spatial extent and affected habitats are not completely recognized, hence restricting regional management actions. We examined the presence, spatial scale and cover of cyanobacterial blooms in different habitats of the reef systems off Old Providence Island, and identified the main bloom forming taxa. Cyanobacteria were registered in four different ecosystems, six geomorphological zones and nine habitats. Benthic cyanobacteria reached 18 to 72 % of the total cover in five habitats, particularly at the northwest, east and southeast portions of the island. These blooms consisted of complex consortia belonging to the genera Okeania, Lyngbya, Symploca, Phormidium, Oscillatoria or Spirulina. A bloom of planktonic cyanobacteria was dominated by Trichodesmium and developed on the fore reef of the island (NW), following heavy rains. These results suggest a potential new stressor for the island's reef complex. Future research should focus on the environmental factors that enable cyanobacterial blooms and their local impact on ecosystems and services.