How temperature and meteorological conditions trigger algal blooms on tropical reefs

Agglomerations of macroalgae have increased globally due to changing oceanic conditions, leading to a rise in studies of blooms driven by socio-economic and ecological impacts. Rhizoclonium-like macroalgae blooms have been reported in estuaries, but their occurrence on tropical reefs remains unexplored. This study, conducted between 2005 and 2018, documents the seasonal occurrence of Rhizoclonium-like blooms on reefs and identifies key environmental drivers. These blooms, first recorded in 2006 and becoming more frequent by 2010, occur annually between May and August. The algae form carpets near the substrate, interacting with organisms like reef-building corals, octocorals, ascidians, and sponges. Statistical analysis links the blooms to increased atmospheric pressure and a wider temperature range. The blooms are not influenced by upwelling or land-based nutrients, suggesting meteorological and temperature factors as key drivers. This is the first documented occurrence of large Rhizoclonium-like blooms on tropical reefs, highlighting the need for further study amid global environmental change.