Climate-driven golden tides are reshaping coastal communities in Quintana Roo, Mexico

Sargassum mats in Mexican bays reduce the biodiversity of coral and seagrass nursery habitats. Three bays in Quintana Roo, Mexico were chosen to determine the environmental stress caused by Sargassum natans and S. fluitans on coral, seagrass and fish populations. For both control sites, Yal Ku Lagoon and Half Moon Bay with little to zero Sargassum cover, benthic communities and the physico chemical characteristics of the waters were not impacted. In Soliman Bay, Sargassum mats cover large areas in the shallows and shore and smother the seagrass and corals. Under the Sargassum mats light and dissolved oxygen levels were significantly lower. Anoxic conditions were found, with levels as low as 0.5 mg/L for oxygen and a 73% decrease in light. Water temperature was 5.2 ± 0.1 °C (mean ± SE) warmer under the Sargassum mats. By determination of weight (grams per day) and growth (mm per day), the stress caused by Sargassum mats in Soliman Bay caused a seven-fold decrease in productivity of T. testudinum compared to other sites. Taxonomic diversity was also reduced with lower biomass and an altered species distribution. To improve these ecosystems, pre-emptive conservation management and protection must be priority for future ecosystem health and biodiversity.