Royal Netherlands Institute for Sea Research

Weeds of Change

Characterizing and Modeling the Sources and Sinks of the “Great Atlantic Sargassum Belt”

The brown macroalgal genus Sargassum, the namesake of the Sargasso Sea which is also known as the "golden floating rainforest of the Atlantic Ocean", is an essential habitat and refuge for many organisms including endemic species. The holopelagic Sargassum species, S. fluitans and S. natans, have historically been geographically constrained to the open waters of the Sargasso Sea and Gulf of Mexico. However, these species have recently begun forming massive accumulations in the Tropical part of the Atlantic Ocean, resulting in unprecedented strandings impacting three continents: the coasts of the Gulf of Mexico, Florida, Mexico, Caribbean-island nations, northern Brazil and western Africa.

A close-up view of Sargassum seaweed from inside the "Great Atlantic Sargassum Belt". Concentrations of this brown macroalga are so high that they can be detected using satellite images from space. Photo Credit: Erik Zettler.

Research objectives

There is uncertainty regarding the sources and sinks of Sargassum. This project addresses the following related key questions:

  1. How are Sargassum subpopulations carried and distributed by ocean currents?
  2. How genetically and physiologically variable are the Sargassum species in the Tropical Atlantic Ocean and how does this impact Sargassum bloom dynamics?
  3. Can we combine geomarkers and biomarkers to infer the recent history of Sargassum species’ composition, distribution, and abundance from the sedimentary record?
  4. Are the accumulations of the last decade the result of environmental changes or a natural range expansion of Sargassum spp.?
  5. What is the basin-scale connectivity of Sargassum and how has it changed over the last decades?

Our international, transcontinental consortium includes interdisciplinary work packages that combine biological modelling, physical oceanography, shipboard and field-oriented physiological experiments combined with laboratory approaches, and a poly-phasic marker approach on current and past Sargassum populations.

A schematic overview of the Weeds of Change research project, with the different work packages (WP) and research themes

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