How citizens can combat invasive seaweed

Sien van der Plank, of the University of Southampton, Kwasi Addo Appeaning and Winnie NA Sowah, lecturers at the University of Ghana, and Philip-Neri Jayson-Quashigah, also of the University of Ghana, write about the battle against golden seaweed

Sargassum is a genus of brown seaweed. Over 300 species are distributed across the world in both temperate and tropical climates. The species fluitans and natans are unique because they spend their life cycle floating on the ocean, never attaching to the sea floor. Other seaweed species reproduce and begin life on the ocean floor.

Pelagic (open-sea) sargassum has been described as the “golden rainforest of the ocean” because of the floating ecosystem it supports in the Sargasso Sea, in the western Atlantic Ocean. It occurs naturally in the Gulf of Mexico and the Caribbean.

Floating sargassum first began arriving en masse on shores across the tropical Atlantic in 2011. Up to 10 000t arrived daily during a particularly severe peak season. Severe years since then include 2015, 2018 and 2022, but every year there is a significant influx. In the Caribbean, there has been good progress in understanding the pelagic sargassum seaweed.

We now have a better idea of where it’s coming from: likely a new southern area of growth.

In 2009 the first reports emerged of pelagic sargassum sightings off the coast of Ghana. Densities have increased annually ever since. In early March 2023, large quantities have again arrived on the shores of the Western Region of the country.

It is beneficial in many ways: marine species such as eels, white marlin and dolphin depend on it for spawning grounds, and commercial fish species including tuna depend on it for food.