Sargassum Summer Sargassum Season: Update November 2011
This is a follow up to Sargassum Summer published here
The migratory birds have moved on. The crabs have molted several times, and along with their invertebrate cousins have enjoyed an extended party of feasting and sex. But with the northern winter approaching, many human migrants and residents feel it’s now their turn to enjoy the beach.
The question on many people’s minds is whether the beaches will be white and sandy or be layered with thick slippery weed. Will they wake up in the morning to find that the clothes they abandoned wildly on the beach the night before (yes we know you did!) are buried under a pile of new weed? These are important questions.
To help you decide, here’s a brief overview of what we know and what remains uncertain to science.
The sargassum stranding was unprecedented. There are apparently neither records nor memories of it occurring previously in St Barths. It was the equivalent of snow falling in Miami that continues for weeks leaving residents and governments baffled. With the sargassum invasion, no one had any experience to understand how long this would last and how much weed would come ashore. Adding to the complexity, local and regional variations in wind and currents rapidly changed the weed’s path. One morning you could sit on the beach at Lorient admiring the lines of weed drifting past offshore while idly doing Rorschach tests with the shapes. A slight overnight shift in the wind and the next morning you could sit on the same beach and watch the seaweed drive into the bay like storm clouds.
By late September it was clear that we had a major seaweed stranding. Government and local businesses increased their efforts to clean up the beaches. Several individuals and homeowners appreciated nature’s gift and took the seaweed home for fertilizer and composting. By late October the island had settled into a working relationship with the weed. Crews responded rapidly and with enough equipment to remove large influxes from beaches frequented by residents and tourists.
The question on many people’s minds is whether the beaches will be white and sandy or be layered with thick slippery weed. Will they wake up in the morning to find that the clothes they abandoned wildly on the beach the night before (yes we know you did!) are buried under a pile of new weed? These are important questions.
To help you decide, here’s a brief overview of what we know and what remains uncertain to science.
The sargassum stranding was unprecedented. There are apparently neither records nor memories of it occurring previously in St Barths. It was the equivalent of snow falling in Miami that continues for weeks leaving residents and governments baffled. With the sargassum invasion, no one had any experience to understand how long this would last and how much weed would come ashore. Adding to the complexity, local and regional variations in wind and currents rapidly changed the weed’s path. One morning you could sit on the beach at Lorient admiring the lines of weed drifting past offshore while idly doing Rorschach tests with the shapes. A slight overnight shift in the wind and the next morning you could sit on the same beach and watch the seaweed drive into the bay like storm clouds.
By late September it was clear that we had a major seaweed stranding. Government and local businesses increased their efforts to clean up the beaches. Several individuals and homeowners appreciated nature’s gift and took the seaweed home for fertilizer and composting. By late October the island had settled into a working relationship with the weed. Crews responded rapidly and with enough equipment to remove large influxes from beaches frequented by residents and tourists.
What is the seaweed forecast?
In November, the winds and currents change. Throughout the winter, St Barths is subject to the influence of storms from the Northeast coast of USA and Canada. Those who travel to St Barths at different times of year often notice that the pattern of sand on several beaches reflect this seasonal change. It is why, on Flammands beach, you find more sand at Ile de France side in winter than in summer. What does all this mean? These conditions make it less likely that the weed will continue to drift towards St Barths or wash ashore. In addition, it is normal for small amounts of sargassum to wash ashore throughout the summer in the Caribbean but not in the winter. These events suggest that the influx will decrease. There is still sargassum weed in the offshore waters and a possibility that the remaining weed can come onshore on some Caribbean island. However, the recent storms did not bring much new weed onto the beaches suggesting that the invasion is at an end or coming to an end.
For those who have written to ask if they will be buried under seaweed if they visit the island in winter, the answer is no. There is also much less weed on the beach than in summer. Those wondering if they will be able to enjoy the beach without worry of seaweed fumes, the answer is yes, you will. For those concerned whether they will be swimming in a blue tropical ocean or a sea of weed, the good news is expect to be swimming in a blue tropical ocean. Will you notice more weed on the beach than in previous years? Yes, but not intrusively so. On the more remote rocky coastlines that are inaccessible to humans and clean up crews you will see the weed sparkling golden in the sunshine. In short, St Barths, compared to other locations, was less affected, and the clean up on tourist beaches has been extensive
Offshore the presence of the weed continues to be a boon to fishermen and to the fishing industry on the island. Fishermen have commented on the increases in their catch. So perhaps one benefit is more fresh local fish at the market and restaurant.
The future forecast
The seaweed invasion was caused by a rare combination of storms and currents (see earlier posting Sargassum Summer), which carried weed from the Sargasso Sea to the Caribbean. There are always small amounts of weed that come ashore in summer but this level of stranding has apparently never been recorded. We have no scientific evidence that this will happen again next year or with any regularity in future years. Equally we have no evidence that we won’t experience the same set of conditions again. This is a rare event that as scientists we study in order to understand and be able to better predict in the future.
In November, the winds and currents change. Throughout the winter, St Barths is subject to the influence of storms from the Northeast coast of USA and Canada. Those who travel to St Barths at different times of year often notice that the pattern of sand on several beaches reflect this seasonal change. It is why, on Flammands beach, you find more sand at Ile de France side in winter than in summer. What does all this mean? These conditions make it less likely that the weed will continue to drift towards St Barths or wash ashore. In addition, it is normal for small amounts of sargassum to wash ashore throughout the summer in the Caribbean but not in the winter. These events suggest that the influx will decrease. There is still sargassum weed in the offshore waters and a possibility that the remaining weed can come onshore on some Caribbean island. However, the recent storms did not bring much new weed onto the beaches suggesting that the invasion is at an end or coming to an end.
For those who have written to ask if they will be buried under seaweed if they visit the island in winter, the answer is no. There is also much less weed on the beach than in summer. Those wondering if they will be able to enjoy the beach without worry of seaweed fumes, the answer is yes, you will. For those concerned whether they will be swimming in a blue tropical ocean or a sea of weed, the good news is expect to be swimming in a blue tropical ocean. Will you notice more weed on the beach than in previous years? Yes, but not intrusively so. On the more remote rocky coastlines that are inaccessible to humans and clean up crews you will see the weed sparkling golden in the sunshine. In short, St Barths, compared to other locations, was less affected, and the clean up on tourist beaches has been extensive
Offshore the presence of the weed continues to be a boon to fishermen and to the fishing industry on the island. Fishermen have commented on the increases in their catch. So perhaps one benefit is more fresh local fish at the market and restaurant.
The future forecast
The seaweed invasion was caused by a rare combination of storms and currents (see earlier posting Sargassum Summer), which carried weed from the Sargasso Sea to the Caribbean. There are always small amounts of weed that come ashore in summer but this level of stranding has apparently never been recorded. We have no scientific evidence that this will happen again next year or with any regularity in future years. Equally we have no evidence that we won’t experience the same set of conditions again. This is a rare event that as scientists we study in order to understand and be able to better predict in the future.
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Petite Cul de Sac in August (see original here) Petite Cul de Sac in mid-November
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Marigot in August Marigot in mid-November