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“5,000 Miles Of Seaweed Coming To Florida’s Coast”

a person holding a flower

Have you been asked about a “5,000- mile-wide blob of seaweed” coming  for Florida’s Coast? Is Florida being overtaken by seaweed? The seaweed being referred to is called Sargassum Seaweed,  a genus of brown algae which includes over 350 species. We see it at Biscayne National Park all the time, especially in the spring and summer*– it’s the floating yellow/brown/orange mats of seaweed that have little “berries” on the branches and often time contain different life (crabs, shrimp, fish, etc.) inside. This past spring (spring 2023) articles started to come out warning of a  “5,000-mile-wide stretch of sargassum seaweed coming to Florida’s coast”.* Maybe you’ve been asked about it or perhaps you’ve seen the articles and wondered about it. The headlines proved to be untrue and misleading as this giant stretch  of sargassum didn’t end up coming to Florida’s coast and it was never going to, but that doesn’t mean  the articles weren’t based in some truth. So, what’s the deal? 

The Sargassum seaweed genus contains  over 350 different species. Only 2 species of  sargassum are holopelagic meaning they live  their entire lives floating on the surface of  the water, never attaching to the seafloor – sargassum fluitans (S. fluitans) and  sargassum natans (S. natans) with each  species containing different morphotypes 3.  These are the two species of sargassum that  we notice floating at the park. They live their  entire lives floating because of two important  adaptations: 1) small berry-like gas bladders  called pneumatocysts that make the seaweed  buoyant and 2) their reproductive strategy  which is called fragmentation which means  when small bits of sargassum break off from a bigger piece, each of the small pieces can grow into new  sargassum. This sargassum floats on top of the water where it gets direct access to sunlight so that it  can photosynthesize and feed itself as it reproduces and splits into different pieces each leading to  more sargassum. So, basically there’s an awful seaweed coming for Florida that has an endless food  supply and is constantly multiplying itself, right? Well, it’s not so simple. This sargassum has a lot of  benefits.

a close up of an animal

As you can see in photos above or at Biscayne National Park in person, sargassum comes in a  sort of clump and these clumps easily connect to each other to form bigger mats of sargassum. This  creates structure in the water which attracts marine life including, crabs, shrimp, fish, turtles, and  much more 4. Life flocks to the sargassum. Test it out for yourself, next time you see some sargassum,  gently scoop up a clump and some sea water in a bucket and take a few minutes to look for living  things hiding in the sargassum!  

For centuries, this floating sargassum has gathered in one general area in the middle of the Atlantic Ocean: the  Sargasso Sea. The Sargasso Sea sits in the middle of huge, swirling, circular ocean current called a gyre where sargassum (along with other things) gets trapped in the middle and forms a large region that’s so big and important it gets its own name. The Sargasso Sea! Christopher Columbus is credited with the first written report of the Sargasso Sea in 1492 when he and his sailors encountered it and feared the giant unfamiliar mats of seaweed and the lack of winds within  the sea might prevent their return home 5. Since then, it’s been surrounded by myth. Regardless, the  Sargasso Sea is a safe haven for life in an otherwise barren stretch of ocean. 

a turtle in the grass

The Sargasso Sea isn’t just one giant blob of  sargassum. It’s really many big mats of sargassum that  together form a generally continuous region of the seaweed.  As mentioned above, the Sargasso Sea is teeming with life.  Many refer to the open Atlantic as a sort of desert where not  much life can thrive in the warm, nutrient poor water. But the  Sargasso Sea challenges that, bringing structure that attracts  life. It’s been referred to as a “golden floating rainforest”6 because so many different creatures live in it. The Sargasso  Sea supports hundreds of different species of marine life  providing shade, shelter, food, and breeding grounds 7. The  sargassum provides habitat for creatures like crabs, nudibranchs, seahorses, pipefish, shrimp, and so much more. There’s even a fish adapted to live in the sargassum called a sargassum fish which lives its entire life in the sargassum! Some loggerhead and green sea turtle juveniles (born off of Florida’s Coast) use floating sargassum for food and shelter and make their way  into the Sargasso Sea where they spend a period of their  lives coined “the lost years.” 8 It’s a crucial period in the sea  turtles’ lives called “the lost years” because after being born on the coast, the turtles disappear for a period lasting up to  several years in the ocean before returning to coastal waters  as large juveniles 9. Until recently scientists didn’t know  much about where they went during  this time. The Sargasso Sea! Beyond that, freshwater eels from America and Europe (both endangered) migrate over 3,000 miles to the sargasso sea to breed 10. Porbeagle shark females migrate from Canadian waters to have pups in the  Sargasso Sea. Humpback whales, species of tuna, and  dolphinfish migrate through the Sargasso Sea.* 

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Genus – The taxonomic rank that is above species which is the most specific category Holopelagic – Marine life, specifically algae, that lives its entire life floating in the water and  never being attached to the substrate or bottom 

Morphotype – A group of different types of individuals of the same species of a population Pneumatocysts – The air bladder of certain algae and aquatic plants that helps them float. The  prefix “Pneumo” refers to the presence of air or relates to respiration. The pneumatophore (gas  bladder) of the Portuguese Man O’ War or the pneumatophore roots of the black mangrove are  examples of this prefix being used. Pneumatocysts are not to be confused with nematocysts, the  stinging cells on jellyfish tentacles 

Fragmentation – A type of asexual reproduction where an organism breaks into smaller pieces  to reproduce 

Photosynthesis – Process by which organisms use the sun’s energy to make food Gyre – Large, swirling current in the ocean. There are 5 major ocean gyres on Earth Algal Bloom – A rapid growth of Algae  

Upwelling – In the context of the ocean, upwelling refers to a type of current where deep water  in the ocean which is nutrient-rich rises towards the ocean surface. Upwelling zones are very  suitable for life because of the supply of nutrients 

Saharan Dust – A cloud of particulate matter (dust) that originates in the Sahara Desert in  Africa and gets transported by winds/air currents to different parts of the Earth one of which  includes Florida during the summer. It can be seen as an orangey haze over Miami in the  summer time