Red seaweed has been washing up on Rhode Island beaches for years, but what is it? This week on Possibly we explain what’s causing this red seaweed to appear, how it’s different from harmful “red tides” and how it might help the planet.

Megan Hall: Welcome to Possibly, where we take on huge problems like the future of our planet and break them down into small questions with unexpected answers. I’m Megan Hall. Today we’re answering a question from listener Lynne Donelly, who saw something a bit unusual:

Lynne Donnely: What is all that red seaweed that I saw on the beach the other day? Where did it come from? What do we use it for?

Megan Hall: To find out, we had Christine Peng and Emma Mejia look into this question. Welcome, Christine and Emma!

Christine Peng: Hi, Megan!

Emma Mejia: Hello!

Megan Hall: So, what was it exactly that Lynne saw on the beach? Should we be concerned about the red seaweed washing up on shores?

Christine Peng: Well Megan, we described the scene Lynne saw to marine ecologist and Salem State University Professor Lindsay Green-Gavrielidis, and she says:

Lindsay Green-Gavrielidis: “That red seaweed is actually a non-native species, called Dasysiphonia japonica. It’s a beautiful, fluffy red seaweed.”

Emma Mejia: Beautiful probably isn’t the word most people would use to describe it…

Christine Peng: It can often be smelly, and swimming in it can be ticklish and uncomfortable, especially if you get it stuck in your hair.

Emma Mejia: Now, a lot of people might be scared of seeing reddish material in the water and think that means there’s a “red tide.”

Megan Hall: A red tide?

Christine Peng: Yes! Red tides are technically known as harmful algal blooms.

Lindsay Green-Gavrielidis: “Harmful algal blooms can refer to seaweeds but it typically refers to teeny teeny teeny tiny microscopic algae”

Christine Peng: These tiny algae feed on excess nutrients in the water, which makes them grow out of control in a “bloom”.

Emma Mejia: They can be dangerous because some of them create toxins, which end up building up in shellfish that humans eat.

Christine Peng: But the stuff Lynne saw? That’s seaweed, which is known as macroalgae.

Megan Hall: So seaweed is bigger algae, which is fine, but the teeny tiny “red tide” algae can be toxic?

Christine Peng: Exactly. One you have to look at through a microscope, while the other is big enough to just pick up with your hands.

Megan Hall: So, should we be worried about the red seaweed washing up on shores?

Christine Peng: Well, the red seaweed on Rhode Island beaches isn’t toxic by itself. But, it can be annoying and even harmful in other ways.

Carol Thornber: “These seaweeds typically are not toxic in and of themselves, but they can be very harmful in terms of the impacts they have on the environment and the impacts they have on our state’s economy.”

Emma Mejia: That’s Carol Thornber. She’s a marine environmental scientist and the Dean of the School for the Environment at UMass Boston.

Carol Thornber: “If you have large amounts of seaweed washing up on our beaches in the middle of the summertime, that can have really significant negative impacts on the part of the economy that runs on tourism”

Christine Peng: For example, mats of decomposing seaweed can suck up oxygen in the water, trap bacteria, and create a smell that keeps people away from the beach.

Emma Mejia: Plus, it makes it harder to catch fish. . .

Lindsay Green-Gavrielidis: “It can be a real problem for the fishing industry because it accumulates in such high quantities that it clogs their nets”

Emma Mejia: Still, seaweed isn’t all bad news. It plays a role in ecosystems, absorbs carbon, and even works as a fertilizer. Today, scientists are looking into ways to use it for biofuel, animal feed, and even alternatives to plastic.

Christine Peng: So, if you see red seaweed on the beach, it might look messy, but it’s not the same as a dangerous red tide. In fact, it could play a role in solving some environmental problems!

Megan Hall: Great! Thanks, Christine and Emma!

That’s it for today. You can find more information, or ask a question about the way your choices affect our planet, at askpossibly.org. You can also subscribe to Possibly wherever you get your podcasts or follow us on Instagram, Facebook, LinkedIn, or Bluesky at “askpossibly”

Possibly is a co-production of Brown University’s Institute for Environment and Society, Brown’s Climate Solutions Initiative, and Ocean State Media.

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