In details

Red tide



Red tide: increase of microalgae in the sea.

What is red tide

In the marine region where sunlight can penetrate, there are organisms that together are called plankton. Among these organisms are microscopic algae. The red tide phenomenon results from the explosive growth of some microalgae species. Some professionals call this process algae blooms.

Main features

We get used to using the name red tide. But the increase in the number of microalgae in the sea does not necessarily lead to the appearance of spots of this color in the water. The spots may also be yellow, orange or brown. Other important features of the red tide:

- It can happen naturally in response to changes associated with the seasons, which interfere with sunlight regime and nutrient availability.

"It can happen by humans, since streams carrying household waste flow into the sea." These residues contribute to excessively increase the concentration of nitrogen and phosphorus on the coast, favoring the reproduction of certain microalgae. That is, eutrophication occurs.

- Since the microalgae population is large, there are more microalgae dying and decomposing. The decomposition of microalgae favors the increase in the number of bacteria that consume dissolved oxygen in water. This leads to limitation on breathing by many organisms.

- Because it causes lower oxygen concentration and greater turbidity of seawater, the red tide introduces changes in the different trophic levels of the marine food chain.

How to fight the red tide?

If it happens on the coast of São Paulo, technicians from the São Paulo State Environmental Company (Cetesb) come to the place. They collect water samples to identify the microalgae species that causes the phenomenon. They can use physical barriers to limit the spread of the spot if they identify algae that eliminate toxins after they die.


Ecological curiosity:

One of the last significant red tides happened in Santos (SP) in 2016 //g1.globo.com/sp/santos-regiao/noticia/2016/08/sado-proibe-sale-and-consumption-of-mollusks-apos- red mare.html. The seaweed population Dinophysis The acuminata was huge. The trade in oysters and mussels was prohibited as they could be contaminated with toxin.