Everything to Know about the Red Tide

All over the news and social media, more and more pictures of mass marine die-offs washing up onto shore are popping up. These pictures and videos are indeed scary, however, they do an excellent job in bringing awareness to the red tide crisis occurring in Florida.

But what exactly is a “red tide”? Well, the red tides here in Florida are caused by a species of algae called Karenia brevis, a type of red algae, or dinoflagellate. When a “bloom” occurs the water may turn a reddish color, hence the name “red” tide. An algae bloom is a rapid increase of an algae population in an aquatic environment and it is this bloom that is devastating coastal ecosystems in Florida.

Fish die at Sanibel Causeway after dying in red tide on August 1, 2018, in Sanibel, Florida. Joe Raedle

The mass die-offs are caused by a combination of toxins produced by the algae and eutrophication. The toxins in red algae target the livers of marine species and cause crystallization which results in organ failure and death. Eutrophication is a process that occurs when an aquatic environment becomes overly enriched in nutrients , which leads to excessive growth of algae. When the algae dies, the decomposition process can result in the depletion of oxygen levels in the water. 

Red algae is not only dangerous to aquatic life, but to humans as well. The algal blooms can release toxins into the air and can cause respiratory health issues, as well as irritate the eyes, throat and nose. These toxins can especially be dangerous to those with asthma or other medical respiratory issues. Red algae can also pose a threat to humans by consumption of seafood exposed to the toxins. Eating seafood that has been exposed to red tide can lead to food poising such as diarrhetic shellfish poisoning (DSP) and ciguatera.

Harmful Algal Blooms. National Oceanic and Atmospheric Administration

Red tides are a natural occurrence, however, with an increase in nutrient pollution caused by human activity, algal blooms have increased in intensity as well as frequency. The red tide on the west coast of Florida is fed by run-off from Florida’s farms but is mainly driven by the excessive nitrogen and phosphorous being released from the Mississippi River.

“We need to learn to mitigate our impacts and be better stewards of the environment,” says Dr. Dale Casamatta, a biology professor at UNF who studies aquatic ecology and systematics primarily targeted towards algae. “We have to reduce our nitrogen and phosphorus loads and that’s usually by farming techniques, planting buffer zones that absorb all that nitrogen and phosphorous before it gets in the water, for example.”


Professor Casamatta says, on a larger scale, the levels of nitrogen and phosphorous must be significantly reduced in order to prevent large red tides from occurring again, however, here are a few ways to reduce your own personal nutrient pollution. For example, if you are a homeowner and have a lawn, opt for not using fertilizer and other nitrogen rich lawn products. If you are a pet owner, try to remember to always pick up after your pet as the poop is rich in nitrogen as well as bacteria that can be harmful to the environment. Also, washing your car at a commercial car wash is better than washing your car at home, because car washes are required to treat the water in a wastewater system rather than going down a storm drain and being directly released into the environment.

Small changes can have a big impact and if enough small changes can be made then maybe we can prevent tides like this from further happening. To get more information on harmful algae blooms, check out these links below:

Dinoflagellates and Red Tides (Scripps Institution of Oceanography)

What is a harmful algal bloom? (NOAA)

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