Sargassum and Coastal Ecosystems

 

Sargassum blocking the sun above a reef.

   

In the 2019 article The Complex Case of the Seaweed That Is Drowning Ecosystems in the Caribbean, author Rodrigo Pérez Ortega interviewed Rosa Elisa Rodríguez Martínez, an ecologist studying coral reefs at the National Autonomous University of Mexico’s institute of Marine Science and Limnology.  Located in Puerto Moralos, twenty-four miles south of Cancun, Martinez had been studying the effects of  Sargassum blooms on the local ecology.

Martinez was one of the first scientists to understand the effects the  Sargassum bloom would have on the coral reefs of the Mexican Caribbean. Starting in 2015, with some respite in 2016 and 2017, the amount of Sargassum washing in increased substantially. The deteriorating water quality coincided with seagrasses near beaches dying off, followed by coral reefs dying from disease.

The increase in  Sargassum is complex, with some blame going to discharge from Brazilian farmers, upwelling, and climate change. Once the  Sargassum reaches the beaches it dies off, causing a “brown tide” as it decomposes in the water. The mass of decomposing material cuts down how much light reaches seagrasses and causes low oxygen levels and higher ammonium and sulfate levels in the water. The deteriorated water and decomposing seaweed have caused wildlife mortality in at least 78 species. Corals have also started dying off from “white syndrome.” Thus far there is no conclusive evidence that the  Sargassum is causing the death of the coral, but it coincides with  the arrival of the  Sargassum bloom in 2018.  Scientists are studying the heavy metals in  Sargassum as well at the macrofauna living on the seaweed to more fully understand its impact and the effects of removing  Sargassum.

Sargassum is having a negative impact on the local community. Tourism suffers due to  Sargassum blooms, leading to layoffs in the local communities.  Economic hardship leads to an increase in crime. Although people are paid to collect the seaweed, the problem is overwhelming.

Read the article!