Some members and guests have commented on the excessive amounts of seaweed that they have seen washing up on the beaches of Cancun, Puerto Morelos and the Riviera Maya in recent weeks. In spite of the efforts of the beach-cleaning brigades at our resorts, patches of seaweed are still coming ashore. This phenomenon was first reported in the summer of 2014 along the Riviera Maya coast, Cancun and other areas of the Mexican Caribbean and has occurred again recently. It is expected to die down in the next few weeks.

Seaweed washing up on area beaches occurs naturally and varies from season to season and according to the weather. Storms and ocean currents dislodge and transport seaweed great distances depositing it on the shoreline. Warmer water temperatures in the summer can also cause excessive algae growth known as blooms. However, such huge amounts of seaweed washing up on the coast have not been seen before.

We contacted the National Autonomous University of Mexico Marine Research Field Station in Puerto Morelos to see if staff could spread some light on this and they gave us the following information. We would like to thank Marine Biologist Rosa Rodriguez, MSc. for sharing it.

This phenomenon is not confined to the Quintana Roo coast, reports of huge amounts of seaweed coming ashore are occurring throughout the Caribbean. Marine biologists do not know yet whether this invasion is a one-off event and if so what caused it or whether it will prove to be cyclical.

The seaweed currently being washed up on our beaches in such large quantities is comprised of two species of pelagic Sargasso known as Common Gulfweed (Sargassum natans) and Broad-toothed Gulfweed (Sargassum fluitans). Both have gas-filled bladders that enable them to float on the surface and move with the currents. Unlike other algae that are rooted in the seabed or attached to rocks or corals, they can grow and reproduce as they drift through the ocean. Both species are harmless to man.

Initially, marine biologists in the Mexican Caribbean thought that the seaweed was local and was proliferating due to an increase in nutrients in the water or that ocean currents were bringing it south from the Sargasso Sea in the Atlantic Ocean. Yet, they now believe it may originate in an area off the coast of South America; a previous seaweed invasion which affected the eastern Caribbean was traced to Brazil.

Scientists throughout the Caribbean and in the United States are working together to track the seaweed as it is carried north, west and east by ocean currents. They want to find out why it is reproducing so quickly and if it is a natural phenomenon or a response to changes in the ocean caused by man, such as rising sea temperatures and more nutrients in the water (fertilizers and other waste products washed into the sea).

An external company cleans the beaches in front of the Cancun resorts three days a week to support the work of our staff. Given the quantity of seaweed washing ashore at this time, it will be providing the service six days a week for the next month.