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Sargassum
Sargassum piles on Padre Island National Seashore. Photo by Bob Beatson.
Many species of crabs, shrimp, and fish spend their entire lives in it.
Locals know it as gulfweed, or simply seaweed.
Tourists call it a nuisance.
Birds call it a buffet.
Sargassum originates in the Sargasso Sea, where it is bound by the Gulf Stream, the North Atlantic Current, the Canary Current, and the North Atlantic Equatorial Current. This system of currents forms the North Atlantic Subtropical Gyre (in oceanography, a gyre is created by a system of rotating ocean currents generated by large-scale wind movements). Sargassum is named for the small, gas-filled bladders that keep surface species afloat and anchored varieties upright. Portuguese sailors traveling across the Sargasso Sea on early voyages to the New World called the weed salgazo, after a small grape native to their homeland. Eventually, salgazo devolved into sargaco, and from that, scientists derived the genus name, Sargassum. Both biologists and laypeople use this term to refer to this type of brown algae, an example of a situation where the scientific name for an organism is also its common name.
The two floating species of Sargassum are Sargassum natans and Sargassum fluitans. There are two major characteristics for differentiating between the two. 1) The leaves of S. natans are long-stalked and narrow; the leaves on S. fluitans are short-stalked and broad. 2) The pods on S. natans are usually tipped with spikes or small leaves, while the pods on S. fluitans are usually not. Thanks to their "little grapes," these species stay at, or pretty close, to the surface and are experts at photosynthesizing at the air-sea interface where solar radiation is quite intense. On the sunniest days, they can decrease light absorption, and on overcast days, they can increase it. Sargassum even has a naturally occurring sunscreen to protect it from UV rays. Because of the interlocking nature of the currents in the Sargasso Sea, only some portions of Sargassum ever exit their languid home. Huge swaths can be pushed out by storms or prevailing winds and may drift through the Caribbean basin or through the Yucatan Straits into the Gulf of Mexico. The Gulf serves as Sargassum's nursery. S. natans and S. fluitans reproduce asexually through fragmentation. Having been split into many pieces on its journey to the Gulf, each fragment grows into a brand new plant. In fact, every piece of the same species may come from a single ancestor. So much Sargassum is "born" in the Gulf that you can even see it from space!
These football-field-sized clumps of Sargassum are beneficial for many offshore species. Aside from the fact that these weed lines seem to attract and hold just about every species of big game fish that anglers pursue, Sargassum has an important role to fill in the life cycles of hundreds of marine animals. Numerous tiny creatures, some perfectly camouflaged by their color and shape, spend part or all of their lives within the floating patches of weed. Seahorses and slender pipefish, for example, are practically indistinguishable from Sargassum's branches, and the Sargassum crab and Sargassum fish mimic the colors and patterns of the seaweed so well they are practically invisible. Juvenile billfish, mahi mahi, swordfish, and even some species of snapper, grouper, and permit seek refuge in the protective stalks. The habitat is often likened to that of the inshore estuary estuaries provide a nursery inshore, and Sargassum provides one offshore. This large presence of juvenile fish is what attracts the highly sought after predatory game fish. The structure of floating Sargassum mats functions like an upside down coral reef, the base of this reef being, not on the seafloor, but drifting along the sea surface. Just as on a coral reef, the smaller fish and marine life hide close to the base, with progressively larger predatory fish stacking up at increasingly greater distances below.
While biologists and anglers generally hold Sargassum in high regard when it floats in the Gulf, opinions seem to sour as it closes in on land. Finding itself trapped in the currents of the Gulf Stream, Sargassum naturally meanders its way toward the beaches of Texas each summer. The large piles of Sargassum and trash that accumulate near the high tide line restrict access to the beach and water and can be hazardous to your health (the trash, not the Sargassum). The decomposing algae adds nutrients to the beach, but this decomposition is also responsible for the foul odor that has offended many a beach stroller. Many coastal cities have dealt with this annoyance by beach raking, which is still a controversial action, probably because the several studies that have been conducted don't all reach the same conclusions.
On one hand, Sargassum acts like a sponge, absorbing wave energy, which protects the sand from wave erosion. Also, the tangled, wet clumps of Sargassum trap sand from wind erosion, helping to build small embryonic dunes that stabilize the beach. Some studies indicate that beach raking increases the loss of sand from wave- and wind-induced erosion by removing the initial barrier that accumulates sand. Erosion of the beach causes loss of nesting area for sea turtles (plus, heavy equipment that scoops up the Sargassum sometimes creates ridges of sand that hinder sea turtles' ability to crawl up the beach), and since erosion can cause destruction of houses on the coast, removal of Sargassum could have adverse economical impacts also. In addition, that's some seagull's lunch you're shoving off!
On the other hand, Sargassum can be a barrier to nesting sea turtles, as well. If they are incapable of climbing over the accumulated weed piles, they end up laying their eggs in the Sargassum instead. The eggs then might be washed out to sea before hatching. Also, at least one study thought about including the impact of beach raking on birds. During the single afternoon set aside for studying birds, the researchers observed that, though a few birds did land on the older deposits of Sargassum at the high tide line, most mainly picked through the fresh Sargassum on the waterline. This indicates that the birds might depend more on fresh influxes of Sargassum than older piles at the high tide line, so birds may not be negatively affected by daily beach raking. As for erosion, some studies showed no difference in beach elevation over a two-year time period between raked and unraked beaches, so the sand that accumulates around Sargassum piles may not be making a significant difference in beach erosion. Where rotting Sargassum does have a positive effect is in the dunes. Sargassum is a natural source of fertilizer for dune plants which help stabilize the dune system from erosion. Research has shown that tannins from Sargassum increase the growth of seeds, and moving the Sargassum clumps from the high tide line to the dunes could beneficially increase growth of the more commonly used plants for dune stabilization. So there are pros and cons either way you look at it, but at least it's only a seasonal concern.
Eventually, the tides turn, and the visiting Sargassum, having doubled in abundance, takes its leave and drifts home to the Sargasso Sea where it continues to encourage rumors of dragging ships down to Davy Jones' locker.
Where I learned about Sargassum, and you can, too!
Sargassum Early Advisory System
www.tamug.edu/SEAS/Index.html
Sargassum & Beach Erosion: Potential Costs & Benefits for Coastal Managers
http://blog.galveston.com/wp-content/uploads/2013/05/seaweed.pdf
Sargassum: Erosion & Biodiversity on the Beach
http://ssl.tamu.edu/media/1828/07_005_10_final_report.pdf
Gulf Restoration Network
https://healthygulf.org/20090709769/blog/healthy-waters-/-dead-zone/sargassum-the-gulf-aamp-texas-beaches-guest-post
Passport to Texas
http://passporttotexas.org/nature-whats-up-with-the-sargassum/
NOAA: Teacher at Sea
http://teacheratsea.wordpress.com/tag/sargassum/
NOAA
http://oceanexplorer.noaa.gov/explorations/03edge/background/sargassum/sargassum.html
Defenders of Wildlife
https://www.defenders.org/sites/default/files/publications/wildlife_and_offshore_drilling_sargassum.pdf
Port Aransas South Jetty
http://www.portasouthjetty.com/news/2011-05-05/Front_Page/Blessing_or_curse.html
Encyclopedia of Life
http://eol.org/pages/893154/overview
The Gulf Stream: Tiny Plankton, Giant Bluefin, & the Amazing Story of the Powerful River in the Atlantic
By Stan Ulanski
Columbus: The Four Voyages
By Laurence Bergreen
Locals know it as gulfweed, or simply seaweed.
Tourists call it a nuisance.
Birds call it a buffet.
Sargassum originates in the Sargasso Sea, where it is bound by the Gulf Stream, the North Atlantic Current, the Canary Current, and the North Atlantic Equatorial Current. This system of currents forms the North Atlantic Subtropical Gyre (in oceanography, a gyre is created by a system of rotating ocean currents generated by large-scale wind movements). Sargassum is named for the small, gas-filled bladders that keep surface species afloat and anchored varieties upright. Portuguese sailors traveling across the Sargasso Sea on early voyages to the New World called the weed salgazo, after a small grape native to their homeland. Eventually, salgazo devolved into sargaco, and from that, scientists derived the genus name, Sargassum. Both biologists and laypeople use this term to refer to this type of brown algae, an example of a situation where the scientific name for an organism is also its common name.
The two floating species of Sargassum are Sargassum natans and Sargassum fluitans. There are two major characteristics for differentiating between the two. 1) The leaves of S. natans are long-stalked and narrow; the leaves on S. fluitans are short-stalked and broad. 2) The pods on S. natans are usually tipped with spikes or small leaves, while the pods on S. fluitans are usually not. Thanks to their "little grapes," these species stay at, or pretty close, to the surface and are experts at photosynthesizing at the air-sea interface where solar radiation is quite intense. On the sunniest days, they can decrease light absorption, and on overcast days, they can increase it. Sargassum even has a naturally occurring sunscreen to protect it from UV rays. Because of the interlocking nature of the currents in the Sargasso Sea, only some portions of Sargassum ever exit their languid home. Huge swaths can be pushed out by storms or prevailing winds and may drift through the Caribbean basin or through the Yucatan Straits into the Gulf of Mexico. The Gulf serves as Sargassum's nursery. S. natans and S. fluitans reproduce asexually through fragmentation. Having been split into many pieces on its journey to the Gulf, each fragment grows into a brand new plant. In fact, every piece of the same species may come from a single ancestor. So much Sargassum is "born" in the Gulf that you can even see it from space!
These football-field-sized clumps of Sargassum are beneficial for many offshore species. Aside from the fact that these weed lines seem to attract and hold just about every species of big game fish that anglers pursue, Sargassum has an important role to fill in the life cycles of hundreds of marine animals. Numerous tiny creatures, some perfectly camouflaged by their color and shape, spend part or all of their lives within the floating patches of weed. Seahorses and slender pipefish, for example, are practically indistinguishable from Sargassum's branches, and the Sargassum crab and Sargassum fish mimic the colors and patterns of the seaweed so well they are practically invisible. Juvenile billfish, mahi mahi, swordfish, and even some species of snapper, grouper, and permit seek refuge in the protective stalks. The habitat is often likened to that of the inshore estuary estuaries provide a nursery inshore, and Sargassum provides one offshore. This large presence of juvenile fish is what attracts the highly sought after predatory game fish. The structure of floating Sargassum mats functions like an upside down coral reef, the base of this reef being, not on the seafloor, but drifting along the sea surface. Just as on a coral reef, the smaller fish and marine life hide close to the base, with progressively larger predatory fish stacking up at increasingly greater distances below.
While biologists and anglers generally hold Sargassum in high regard when it floats in the Gulf, opinions seem to sour as it closes in on land. Finding itself trapped in the currents of the Gulf Stream, Sargassum naturally meanders its way toward the beaches of Texas each summer. The large piles of Sargassum and trash that accumulate near the high tide line restrict access to the beach and water and can be hazardous to your health (the trash, not the Sargassum). The decomposing algae adds nutrients to the beach, but this decomposition is also responsible for the foul odor that has offended many a beach stroller. Many coastal cities have dealt with this annoyance by beach raking, which is still a controversial action, probably because the several studies that have been conducted don't all reach the same conclusions.
On one hand, Sargassum acts like a sponge, absorbing wave energy, which protects the sand from wave erosion. Also, the tangled, wet clumps of Sargassum trap sand from wind erosion, helping to build small embryonic dunes that stabilize the beach. Some studies indicate that beach raking increases the loss of sand from wave- and wind-induced erosion by removing the initial barrier that accumulates sand. Erosion of the beach causes loss of nesting area for sea turtles (plus, heavy equipment that scoops up the Sargassum sometimes creates ridges of sand that hinder sea turtles' ability to crawl up the beach), and since erosion can cause destruction of houses on the coast, removal of Sargassum could have adverse economical impacts also. In addition, that's some seagull's lunch you're shoving off!
On the other hand, Sargassum can be a barrier to nesting sea turtles, as well. If they are incapable of climbing over the accumulated weed piles, they end up laying their eggs in the Sargassum instead. The eggs then might be washed out to sea before hatching. Also, at least one study thought about including the impact of beach raking on birds. During the single afternoon set aside for studying birds, the researchers observed that, though a few birds did land on the older deposits of Sargassum at the high tide line, most mainly picked through the fresh Sargassum on the waterline. This indicates that the birds might depend more on fresh influxes of Sargassum than older piles at the high tide line, so birds may not be negatively affected by daily beach raking. As for erosion, some studies showed no difference in beach elevation over a two-year time period between raked and unraked beaches, so the sand that accumulates around Sargassum piles may not be making a significant difference in beach erosion. Where rotting Sargassum does have a positive effect is in the dunes. Sargassum is a natural source of fertilizer for dune plants which help stabilize the dune system from erosion. Research has shown that tannins from Sargassum increase the growth of seeds, and moving the Sargassum clumps from the high tide line to the dunes could beneficially increase growth of the more commonly used plants for dune stabilization. So there are pros and cons either way you look at it, but at least it's only a seasonal concern.
Eventually, the tides turn, and the visiting Sargassum, having doubled in abundance, takes its leave and drifts home to the Sargasso Sea where it continues to encourage rumors of dragging ships down to Davy Jones' locker.
Where I learned about Sargassum, and you can, too!
Sargassum Early Advisory System
www.tamug.edu/SEAS/Index.html
Sargassum & Beach Erosion: Potential Costs & Benefits for Coastal Managers
http://blog.galveston.com/wp-content/uploads/2013/05/seaweed.pdf
Sargassum: Erosion & Biodiversity on the Beach
http://ssl.tamu.edu/media/1828/07_005_10_final_report.pdf
Gulf Restoration Network
https://healthygulf.org/20090709769/blog/healthy-waters-/-dead-zone/sargassum-the-gulf-aamp-texas-beaches-guest-post
Passport to Texas
http://passporttotexas.org/nature-whats-up-with-the-sargassum/
NOAA: Teacher at Sea
http://teacheratsea.wordpress.com/tag/sargassum/
NOAA
http://oceanexplorer.noaa.gov/explorations/03edge/background/sargassum/sargassum.html
Defenders of Wildlife
https://www.defenders.org/sites/default/files/publications/wildlife_and_offshore_drilling_sargassum.pdf
Port Aransas South Jetty
http://www.portasouthjetty.com/news/2011-05-05/Front_Page/Blessing_or_curse.html
Encyclopedia of Life
http://eol.org/pages/893154/overview
The Gulf Stream: Tiny Plankton, Giant Bluefin, & the Amazing Story of the Powerful River in the Atlantic
By Stan Ulanski
Columbus: The Four Voyages
By Laurence Bergreen