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What You Need to Know About San Diego's Red Tide

Allison Cusick is a graduate student at the Scripps Institution of Oceanography studying phytoplankton in Antarctica. Here are her answers to your top questions about the red tide:

What is the red tide? 

A red tide is a bloom of a microscopic algae called phytoplankton. Think of it as a super bloom for the ocean. In San Diego, we are currently seeing a bloom of phytoplankton called  'dinoflagellates,' which translates from Greek and Latin to 'whirling whip,' in reference to the shape of this organism. The specific species is Lingulodinium polyedra.

What's with the bioluminescence?

Bioluminescence is a chemical reaction caused within individual cells of phytoplankton when they are agitated. At night, we are seeing waves on the coast glow electric blue — that’s the result of chemical reactions within millions of phytoplankton reacting to the agitation caused by those waves.  Bioluminescence has actually evolved a number of times throughout history in fish, jellyfish, phytoplankton and worms; and can serve as a tool for communication in the ocean.

Is the red tide normal? What caused it? Can it be linked to climate change?

Red tides are common occurrences in San Diego and around the world. Red tides can be caused by a couple of factors, including large rain events that carry nutrients towards the coast. They can also occur with reduced upwelling in the ocean, which causes water near the surface of the ocean to be warmer and more hospitable than usual to certain species of phytoplankton. Scientists have identified an increasing number of red tides in recent years but more research is needed to understand the potential connection with climate change.

How long will it last?

We don't know. That's part of the magic! A red tide in 2019 in San Diego lasted about 2 weeks, but one in 1995 lasted three months.

Is it dangerous to humans?

The species of phytoplankton blooming along San Diego's coast right now is not toxic to humans. However, phytoplankton excrete a lot of compounds that get released into the air. Some people can be sensitive to this, and it can cause quite the smell. The breakdown of the algae is also causing foam to build up on the beach.

Is it dangerous to marine life?

Large concentrations of phytoplankton can get in the way of marine predators that use their eyes to hunt. Researchers at the Scripps Institution of Oceanography are also working to determine whether the red tide can be linked to fish die offs that are being reported around the region.

video and banner image by Shayna Brody