“5,000 Miles Of Seaweed Coming To Florida’s Coast”
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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.
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.
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.*
Glossary
∙ 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