The Gulf Coast of Florida is already dealing with two different algae blooms: a red tide on many beaches south of Manatee County and blue-green algae spilling into the Gulf from Lake Okeechobee; but now outbreaks of a larger species of seaweed have even reached Florida. Beginning about seven years ago, beaches throughout the Caribbean Sea have been swamped by feet-thick blooms of Sargassum.
Amy Siuda is an assistant professor of marine science at Eckerd College in St. Petersburg and is trying to figure out if this Sargassum is a different species than is commonly found in the Caribbean.
“Sargassum is a brown algae, a type of seaweed, that is common throughout the tropics and temperate region. There are hundreds of species of Sargassum and most are attached to the bottom like normal seaweeds. But there are two species that are known right now — of Sargassum — that live their entire lives not attached to the bottom. So those two species have been associated with the Sargasso Sea out in the center of the North Atlantic [Ocean].”
And oftentimes critters live right among these floating algae.
“Yes, Sargassum serves as this, kind of, oasis of life in the middle of the open ocean. So, it’s been called a pseudo-benthic habitat. A habitat that organisms can live within the seaweed from tiny algae — single-celled algae — to small shrimps and crabs that live in the algae and then larger fish come and feed on those smaller organisms. So there tends to be this abundance of life around Sargassum out in the middle of the ocean. Where when you’re away from a Sargassum mat out there you kind of just see blue water and nothing else.”
But since 2011 something has changed and you’re getting these massive mats of Sargassum washing up on Caribbean beaches.
“It’s been pretty interesting. There doesn’t seem to be any knowledge of these inundations happening historically. There’s no real record of them. So Sargassum has been washing ashore periodically — 2011, then again in 2014, 2015 and now again this year — we’re getting big inundations of Sargassum. That means feet high of Sargassum washing ashore in the Caribbean. For me, this is an interesting question because there are these — what is typically an oceanic seaweed and a community that lives around that — is now coming ashore, covering coral reefs, covering beaches, interacting with coastlines. And normally these two habitats don’t interact, don’t meet each other.
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“It’s been causing challenges to tourism, to turtle reproduction and nesting on beaches. It hasn’t been a very positive experience for the Caribbean islands because it’s coming in in such masses and they’re trying to figure out how to get it off the shores.”
And they’re causing massive turtle kills. The Barbados government declared a national emergency in June.
“Yes, the challenge of trying to remove this feet-deep of seaweed that’s washing ashore on the beaches, in a safe way without damaging turtle nests in the process.”
We don’t know for sure what’s causing it, but what are some of the ideas about why that might be?
“We’re finding that this Sargassum that’s inundating the Caribbean, there’s evidence that it’s coming from the tropical or equatorial Atlantic rather than the Sargasso Sea to the north. And colleagues of mine have shown by tracing currents backwards that it’s coming from that area. We also have satellite evidence that it’s coming from that area. We’ve seen this type of Sargassum before, just not in this abundance. So there may have been this low-abundance there in the past, but now we have increasing nutrients from changes in [ocean water] mixing, maybe causing nutrients to come to the surface. We may have increased temperatures from warming that are causing the Sargassum to grow faster and become more abundant. There may be atmospheric dust inputs coming off of Africa that are adding micronutrients that are important for algae growth. So we’re not really sure what’s causing this, we’re just starting to look at that now.”
You are researching whether this might be a different species than the one that’s normally seen in the Caribbean.
“Yes. We have some initial supporting evidence, but this type of Sargassum that’s coming ashore in the Caribbean, we noticed a number of years ago when it first started coming ashore, that it looked similar but had a slightly different shape to it. A different morphology. It has broader leaves and is not as dense as the two species of Sargassum that are typically found in the middle of the Sargasso Sea. This form of Sargassum has been identified in the past. It’s considered one of the two species, just a separate shape, or a different morphology. But right now we are looking into whether it actually can be classified as a separate species. We’re looking both at the morphology and the genetics very carefully to try to see if it actually is a separate species from the other two more common forms.”
And finally, I should ask: how widespread are these large mats of Sargassum in the Caribbean? Is it over the entire island chains?
“So, they’re blooming in the equatorial Atlantic and the Sargassum is actually coming ashore in the coast of Africa as well as the Caribbean shorelines. So they’re hitting coastlines from north to south through the Caribbean islands, up to Antigua and down to Tobago. And then it’s coming through the Caribbean and actually making its way across to Mexico and into the Gulf of Mexico as well.”
And we know what the next stop would be there — maybe Florida?
“Yes. Yes. So, in the past, in the last two major inundations, the Sargassum has made it, actually, all the way up in the Gulf Stream all the way up to the coast of New England.”