Algae Problem in the Caribbean Sea

One thing I soon noticed during my Erasmus stay in Guadeloupe was the nuisance of algae. The kind of brown algae flooding the Caribbean Sea is called Sargassum. They have the power to turn beautiful beaches into stinking pots. White sand is hidden under enormous masses of brown piles; clear blue water is spoiled with long fibrous plants. Environmentalists and locals agree that there is an Algae Problem in the Caribbean Sea. What happened here? Where do all the algae come from? Is this a natural phenomenon or a human self-trap?

Algae – Plant or bacteria?

Today humans know about 30 000 kinds of algae. To understand the problem Caribbean beaches are facing, it may be interesting to learn a bit more about these organisms in general. What are they? Are they plants, are they bacteria? The answer is they are both. Algae are not a group in a biological sense. The term is used to describe organisms descending from different ancestors. This means they are not closely related to each other. The blue algae, also called Cyanobacteria, belongs to Bacteria. Like all bacteria, they don’t have a real cell nucleolus, they are Prokaryotes. Other algae, such as green algae, are Eukaryotes, which means they have a real cell nucleolus. Eukaryotic algae can occur as single cells or multicellular. This is the reason why their size can vary from one micrometer to several meters. ¹ However, not all eukaryotic algae are plants! Only the green algae and the stoneworts are considered plants. ² The brown algae spoiling Caribbean beaches, the sargassum, is not a plant.

Where do the algae in the Caribbean Sea come from?

Floating Algae in the Atlantic is not a new phenomenon the Study The great Atlantic Sargassum ³ belt suggests. However, its abundance and density highly increased since 2011. In 2018 the algae belt counts 8850 kilometres (source). It expands “from West Africa to the Caribbean Sea and [the] Gulf of Mexico” (Wang et. al, 2019). ³

The Study indicates that the Sargassum might source from the West Africa. On the coast, sea currents transport cold water containing a lot of nutrients, to the surface. These abundance of nutrients transported into the Atlantik causes the algae to grow on a larger scale.  ³ You can compare this addition of nutrients to fertilizing a field. Plants grow more extensively, until a certain degree. The surplus of nutriments accelerates their growth. However, the question remains: Why do the algae bloom now so heavily since the addition of sustenances from the West African coast is not a new phenomenon?

The theory exists, that the discharge of nutrients into the Amazonian river plays a role in algae accumulation. Due to the clearage of the Amazonian forest, the freed land is used for agriculture. The fields’ fertilizer can end up in the Amazonian river, which flows into the Atlantic. In this way, the discharge of nutriments reaches the beaches of the Antilles. ³

The ecological consequences of the Sargasso

I found it quite astonishing that these algae have a negative ecological impact on the flora and fauna. Aren´t algae a really important oxygen provider and therefore important for ecosystems? So what are the consequences of the Algae Problem in the Caribbean Sea?

On one hand, also the Sargassum is important for marine Ecosystems. It provides habitats for fish, crabs, birds, and turtles. ³

On the other hand, the degradation process of Sargassum on beaches produces Ammoniac and Hydrogen Sulphate. This mixture is toxic and creates the smell of rotten eggs. ⁴

Another ecological problem the massive increase of sargassum is causing is the blockage of sunlight. When the layer of Sargassum becomes very dense it obstructs the passage of sunlight through the water surface. This leads to a lack of available sunlight for corals and water plants, which can reduce photosynthesis. ⁴

Apart from the ecological problems the Sargassum also has a negative impact on tourism. ⁴ This is quite relatable since you expect from a trip to the Caribbean white sand and blue water and not a smelly brown beach.

Conclusion

What do we learn from this algae problem in the Caribbean sea? I find this a very interesting example of the connection of different ecosystems on Earth. Who would have thought that cold water on the West African Coast can influence the algae accumulation in the Caribbean Sea? Or that the fertilizer used in the Amazonas has an impact on the tourism in the Antilles?

References:

1. Véto-Leclerc, Véronique and Jean-Ives Floc´h., 2019. Les secrets des algues. second edition. Versailles : éditions Quae.
2. Savada, David., Hillis, David M., Heller, H. Craig and Hacker, Sally D. 2019. Purves Biologie. tenth edition. Heidelberg: Springer Spektrum.
3. Wang, Mengqiu., Hu, Chuanmin., Barnes, Brian B., Mitchum, Gary., Lapointe, Brian and Montoya, Joseph P. 2019. The great Atlantic Sargassum belt. Science. Vol 365, Issue 6448, 83-87.
4. Lagons Plages., s.a. Les sargasses, ces algues qui font du mal. https://www.lagons-plages.com/sargasses-caraibes.php [25.09.2022].