Sargassum Seaweed on Tybee by Joe Richardson

Posted By Charissa / July 5, 2012 / , , , / 0 Comments

During late June, the smell of seaweed on Tybee’s beach reminded me of my graduate school days!! I did most of my doctoral research on seaweeds, so I made lots of trips to various coastlines (both east and west) collecting and studying seaweeds. In my lab, I worked with lots of seaweeds (both dead and alive). And in my car, I carried lots of seaweeds. So this was a very familiar and somewhat nostalgic smell for me, that I don’t often notice at Tybee. I’ve been getting a few calls, emails and messages asking, “where did all this seaweed come from?” Here’s probably more than you really want to know (but those who know me, know that I’m not good at giving short answers)!

This is the most Sargassum seaweed I’ve ever seen on Tybee. This species of Sargassum (a brown seaweed) is unlike most seaweeds, that have to grow attached to a hard bottom or structure in shallow water where they get enough light to do photosynthesis. This Sargassum actually grows unattached, floating in open water, generally well out in the Atlantic Ocean. In fact some charts refer to the middle of the Atlantic Ocean as the “Sargasso Sea” because there is lots of it floating around out there. The small berry-looking structures on the Sargassum are actually air floats that keep it floating near the surface. Clumps of Sargassum in the open ocean serve as places to hide for some animals and as structure for some small animals to attach on to. During late June, we found lots of those small animals (Sargassum shrimp, Sargassum Swimming crabs, small file fish, baby flying fish) on the beach and in tide pools because they have washed in with the seaweed clumps. All these animals are yellow-orange in order to camouflage or blend in with the seaweed. So the Sargassum has brought with it lots of interesting animals from far offshore, that we normally don’t see on our beach.

The floating clumps of Sargassum in the open ocean also serve as places to hide for small young animals that will eventually become larger as they age and grow. When the baby Loggerhead Sea Turtles hatch on Tybee’s beach later this summer, they will head out to sea, and many will hide among clumps of floating Sargassum far offshore. Many years ago, while on a research cruise offshore, we anchored overnight and found ourselves among a large area of floating Sargassum. Being curious scientists, we used some long dip nets to catch some clumps of the floating seaweed to see what sort of animals were among it. This was how I caught the only Sailfish I’ve ever caught!

So, if the Sargassum normally lives far out in the Atlantic, why did it wash ashore here? I don’t recall our having a prolonged period of strong winds from the east, so I don’t think it was necessarily a wind-blown event. Instead, I’ve got a different hypothesis (guess). The Gulf Stream current flows from the south toward the north well offshore of Georgia’s coast. It doesn’t flow in a straight line, but meanders alot. Sometimes those meanders can be almost like huge hair-pin curves, and sometimes those big meanders, like loops, can break off and form large circular or oval water masses of warm off-shore water. If such a large ring of Gulf Stream and warm Atlantic Ocean water (and possibly water that recently had been in the tropics) happened to break off on our side of the Gulf Stream, it could gradually move toward our coast, and bring with it things like Sargassum. This is my guess: one of these offshore water masses, with its floating Sargassum, broke off and has moved into our coastal waters.

Since the Sargassum seaweed event on Tybee, I’ve been noticing (almost daily while conducting my Tybee Beach Ecology Trips) additional tropical and offshore species of animals. Right now there is a group of Sargent Majors, a small black and white striped damsel fish that is common around coral reefs and rocky shorelines in the Caribbean and Florida Keys. They don’t belong this far north. We recently also got a Ballyhoo, a strange looking fish with a long extended lower jaw; and they usually live offshore where they are food for large gamefish like sailfish, marlins and dolphins.

So I’ve got a feeling that the Sargassum and all these other interesting tropical and offshore animals are signs that Tybee has been the landfall of a large warm water, open-ocean water mass. It sure has made beach ecology on Tybee interesting this spring and summer!!

Dr. Joe Richardson is a marine biologist who conducts research through Coastal Environmental Analysis, and conducts beach ecology trips on Tybee Island through Tybee Beach Ecology Trips www.ceasurf.com/pages/beachtrips.aspx

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Photos
1. Sargassum seaweed accumulated along the high tide line all along Tybee Island beach.
2. Pile of Sargassum seaweed along the high tide line at North Beach.
3. The berry-like structures on the Sargassum are actually air floats that keep the seaweed at the sun-lit surface.
4. Sargassum shrimp (this one carrying eggs under her abdomen) were abundant in some of the clumps of seaweed.
5. This was one of many Sargassum Swimming Crabs that were common for a few days on Tybee’s ocean beach.
6. Small filefish with camouflage colors matching the seaweed were found among many of the Sargassum clumps.
7. Although only about an inch long, what appears to be a baby flying fish was another type of fish found among the drifting seaweed.
8. Baby Sailfish hide among the floating clumps of Sargassum far offshore.
9. Laying among a pile of Sargassum seaweed along the high tide line was this lumber that had been drifting offshore long enough for these Goose-neck Barnacles to settle and grow. This species of barnacle only grows on drifting, open-water objects.
10. Small Sargent Major damselfish, common on coral reefs and tropical rocky shorelines, have shown up on Tybee in the last week.
11. We’ve been seeing Ballyhoo in the beachwater, but they normally live in warm offshore open waters.

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