Red Tides and Eutrophication

Red tides and eutrophication are two interconnected environmental phenomena that have significant impacts on marine ecosystems. Surprisingly, these topics might have been eluded during biology lessons. This article will delve into red tides and eutrophication and shed light on its profound implications on our oceans and day-to-day lives.

Red tides

Although all bodies of water contain algae, a red tide occurs when algae grows out of control. The term ‘red tide’ comes from the discoloration of water caused by the excessive algae growth, which can manifest as shades of red, green or brown in the waters.

The change in colour occurs due to the overpopulation and density of algae inhabiting the water. While red tides have existed long before humans, specific human activities, such as the use of chemicals in farming or factories, contribute to their increased frequency. These substances can dissolve in water and eventually result in run-off onto the land. Eventually, this run-off flows into the ocean, accelerating the growth of algae and leading to the occurrence of red tides.

Why are red tides dangerous?

Certain species of algae, specifically causing red tides, can produce harmful toxins that kill other organisms like fish, shellfish, mammals, and birds. If humans consume these contaminated animals, there will be severe health consequences. Some other algal blooms are caused by non-toxic algae species, but can also cause trouble - this is known as eutrophication, which will be outlined further in the article.

The giant masses of algae bloom eventually die and decompose. As they decay, oxygen levels in the water begin to decrease and can kill organisms in the surrounding waters or cause them to swim away. This destroys the marine ecosystem and food web.

During and after a red tide event, the nearby beaches may become strewn with deceased fish and other animals, primarily those that either ingested toxins or were unable to obtain sufficient oxygen.

Eutrophication

Eutrophication is the process in which a body of water has excessive richness of nutrients, causing the dense growth of simple plant life. Harmful algal blooms, dead zones, and fish kills are some results of this process.

This sets off a chain reaction in the ecosystem, starting with the overabundance of algae and plants. As mentioned before, when these algae and plants begin to decay, there is a decrease in oxygen levels and increase in carbon dioxide levels.

The increased carbon dioxide levels lower the pH of the seawater, resulting in ocean acidification. This low pH environment leads to less carbonate ions, which are crucial building blocks of structures such as sea shells and coral skeletons.

The decrease in carbonate ions can make it difficult for calcifying organisms that rely on their shells to build and maintain shells or other structures. Additionally, lower pH levels can decrease some fish's ability to detect predators, which puts these organisms at risk and could disrupt the entire food web. 

While red tides and eutrophication may not directly affect human life, they significantly disrupt marine ecosystems and have the potential to disturb our everyday routines in the near future.

Works Cited

NOAA (2021). What is eutrophication? [online] National Ocean Service. Available at: https://oceanservice.noaa.gov/facts/eutrophication.html.

NOAA (2024). What Is Ocean Acidification? [online] Noaa.gov. Available at: https://oceanservice.noaa.gov/facts/acidification.html.

Scijinks.gov. (2016). What Is a Red Tide? | NOAA SciJinks – All About Weather. [online] Available at: https://scijinks.gov/red-tide/.