What nutrient sources support anomalous growth and the recent sargassum mass stranding on Caribbean beaches? A review.

Since 2011, tropical beaches from Africa to Brazil, Central America, and the Caribbean have been inundated by tons of sargassum seaweed from a new equatorial source of pelagic sargassum in the Atlantic. In recent years the extraordinary accumulations of sargassum make this a nuisance algal bloom for tropical coasts. In 2018 satellite data indicated floating mats of sargassum that extended throughout the Caribbean to the northeast coast of Brazil with the highest percent coverage over the water yet recorded. A literature review suggests that Atlantic equatorial recirculation of seaweed mats combined with nutrients from several possible sources may be stimulating the growth and accumulations of sargassum. In the western equatorial recirculation area, new nutrient sources may include Amazon River floods and hurricanes; in the eastern equatorial recirculation area, nutrient sources that could sustain the sargassum blooms include coastal upwelling and Congo River freshwater and nutrients.

Caribbean corals in crisis: record thermal stress, bleaching, and mortality in 2005.

BACKGROUND: The rising temperature of the world's oceans has become a major threat to coral reefs globally as the severity and frequency of mass coral bleaching and mortality events increase. In 2005, high ocean temperatures in the tropical Atlantic and Caribbean resulted in the most severe bleaching event ever recorded in the basin. METHODOLOGY/PRINCIPAL FINDINGS: Satellite-based tools provided warnings for coral reef managers and scientists, guiding both the timing and location of researchers' field observations as anomalously warm conditions developed and spread across the greater Caribbean region from June to October 2005. Field surveys of bleaching and mortality exceeded prior efforts in detail and extent, and provided a new standard for documenting the effects of bleaching and for testing nowcast and forecast products. Collaborators from 22 countries undertook the most comprehensive documentation of basin-scale bleaching to date and found that over 80% of corals bleached and over 40% died at many sites. The most severe bleaching coincided with waters nearest a western Atlantic warm pool that was centered off the northern end of the Lesser Antilles. CONCLUSIONS/SIGNIFICANCE: Thermal stress during the 2005 event exceeded any observed from the Caribbean in the prior 20 years, and regionally-averaged temperatures were the warmest in over 150 years. Comparison of satellite data against field surveys demonstrated a significant predictive relationship between accumulated heat stress (measured using NOAA Coral Reef Watch's Degree Heating Weeks) and bleaching intensity. This severe, widespread bleaching and mortality will undoubtedly have long-term consequences for reef ecosystems and suggests a troubled future for tropical marine ecosystems under a warming climate.