The Golden Tides – Sargassum
XpBonaire IslandLife Feature Story
Bonaire has been facing a flood of Sargassum algae again this year. The foul smell of rotting algae on shore and in the shallow waters was noticeable all over the island. Starting at the end of February, 2019, the organizations that protect nature came up with a plan of action to battle the phenomena that has a negative impact on the island’s tourism, economy and nature. Like last year, 2018, the call for help was answered and many took it upon themselves to assist in clearing the coast.
Reports of unprecedented levels of Sargassum have been documented since 2011, but it is still unclear exactly why the amount of Sargassum has been increasing in recent years, making the Caribbean islands struggle.
Bonaire has another problem also screaming for a solution that is thought to be connected to the Sargassum, the death of many flamingo chicks and juveniles. In 2018, many flamingo juveniles and chicks were found and brought to the wild bird rehab, unable to survive by themselves, starved and dehydrated. More than 150 birds were brought to the rehab center to be nursed until they were strong enough to set free again. According to experts, it seems that the algae are destroying the breeding areas and the necessary food.
What is Sargassum?
Called Sargassum, a term for the brown algae/seaweed that was coined by Portuguese sailors in a 1492 expedition, it was the first time someone reported crossing the Sargasso Sea. Small gas-filled spheres resembling berries, which keep the seaweed afloat, evoked memories of a type of grape known as salgazo (later sargaço).
There are many species of the seaweed genus, Sargassum, distributed throughout the oceans of the world. They can be found in shallow waters were they grow attached to rocks or coral reefs or free floating in the open ocean. Many species of Sargassum have been identified, but Sargassum natans and Sargassum fluitans are the most relevant to us. The vegetative body, or thallus, of Sargassum is tough and leathery, resembling a stem with leaves. They have small, round, gas filled bladders that grow along the stem and help to keep them afloat.
At first glance, beach-lovers might view it as nothing more than a foul-smelling annoyance. However, do remember that the once floating mats were home to and source of food for a huge variety of sea life. In fact, several creatures like the Sargassum fish, a type of frogfish, are born, reproduce, and die solely within this environment!
Where did it come from?
Experts think that the Sargassum we are currently dealing with originated off the coast of South America. When ocean conditions are ripe, pelagic Sargassum can form “islands” a few acres across and 3-5 ft. deep. Sargassum can survive a wide range of temperature and salinity; therefore, you’ll find it floating in every ocean except the Antarctic.
On the other hand, within the Sargasso Sea, a sea full of Sargassum as the name suggests, is a vast region in the Atlantic that almost rivals Australia in size and weighs about 10 million tons.
The Seasonal Movement of Sargassum
Studies tracking Sargassum have found a consistent pattern of movement from year to year, corresponding to prevailing surface currents and wind movements. The Gulf of Mexico acts as a nursery between March and June each year. In the spring, the Sargassum is exported by the Loop Current and Gulf Stream to the Sargasso Sea. Once there, it is trapped by eddies that break away from the southern edge of the Gulf Stream and spin into a central gyre. It accumulates over the summer forming massive rafts tens of meters in diameter that coalesce into continuous features extending hundreds of kilometers. It is estimated that more than 1 million wet tons of Sargassum are exported to the Atlantic each year. The Sargassum appears to die off in winter time and be replenished the following year.
What is the Sargasso Sea?
The Sargasso Sea, which exists exclusively in the Atlantic Ocean (specifically, in the North Atlantic Gyre) is 1,107 km wide and 3,200 km long – approximately 2 million square miles. (Mexico is merely 761,610 square miles). The only sea without fixed land boundaries, its limits are formed by dynamic ocean currents. Several kinds of algae float across oceans worldwide; however, the species of Sargassum found here are “holopelagi”, meaning they float and reproduce on the high seas, not on the ocean floor.
In the Sargasso Sea, the large mats provide refuge for migratory species and essential habitat for more than 120 species of fish, including billfishes and offshore game fishes such as dolphin fish and more than 120 species of invertebrates (Franks and Gibson 2011, Doyle and Franks 2015). Turtles use the Sargassum mats as nurseries where the hatchlings can find food and shelter. When washed up on shore, the seaweed provides food and habitat for intertidal organisms which then support shorebirds and shore scavengers. The decomposing Sargassum provides nutrients to coastal soils helping to establish vegetation and dune development).
Why so much?
Sargassum reproduction is asexual, which means that every bit of the same species could probably be traced back to its original ancestor; therefore, some consider it the largest organism in the world! Due to tot potency (a cell’s ability to give rise to unlike cells and develop a new organism), when a part breaks away, it’s not the end of it. The fragment drifts and could seemingly reproduce forever. Nonetheless, Sargassum eventually becomes too heavy, less buoyant, and sinks into the deep sea or goes coastal!
2011 – The Year of the Great Sargassum Pileup
Something happened in 2011 to produce an ocean-wide explosion of Sargassum that stretched from the Caribbean to the coast of Africa. Unprecedented quantities of seaweed came ashore on coastlines on both sides of the Atlantic. Previously there had been sporadic episodes of the seaweed washing up on beaches, but nothing on this scale.
The giant seaweed bloom didn’t originate in the Gulf of Mexico as was first thought. Instead, the major source of Sargassum was a high-nutrient region offshore Brazil near the mouth of the Amazon, an area not previously associated with Sargassum growth. The origin of the Sargassum and anomalous circulation patterns during this period meant the Sargassum never reached the Gulf Stream, so was not transported to the Sargasso Sea region where it normally accumulates in the summer. Instead it circulated northwards from the coast of Brazil and bloomed in an area in the Atlantic termed the North Equatorial Recirculation Region (NERR; Johnson et al 2013). It has been suggested that it was flushed out of this region in 2011 when the North Equatorial Counter Current broke down. Released, it washed ashore in unprecedented volumes in the Caribbean, building up to depths of more than 2 meters in places. It also drifted eastward to West Africa, washing up on beaches in Sierra Leone, Liberia, Côte d’Ivoire and Benin.
Impact of Sargassum
Similar events have been observed since the 2011 great Sargassum pileup. There is uncertainty about whether the “golden tides”, as they are often referred to, will be an annual occurrence. However, 2015 has seen a severe influx of Sargassum on both sides of the Atlantic, similar in magnitude to the 2011 event. The large volumes of rotting seaweed have affected tourism in the Caribbean and coastal fishing in West Africa. There is growing concern regarding the potential for increased social, environmental and economic damage if the golden tides continue to appear, especially on tourist beaches and important ecological sites. As the large quantities of seaweed rot, they consume oxygen, killing fish and other organisms. When washed onto turtle nesting beaches, they pose a major threat to baby turtles, who struggle through the Sargassum barrier to reach open water.
The reasons for the change in Sargassum distribution that has led to these golden tides is uncertain, but they may include increased nutrients from the Amazon and Orinoco Rivers (as a result of deforestation and agriculture), warmer sea surface temperatures and changes in ocean circulation patterns associated with climate change.
Sargassum provides a food source, home, and shelter to an amazing variety of marine species (plant, shrimp, crab, bird, fish, turtle and whale).
Turtles use Sargassum mats as nurseries. Five species of sea turtles that pass through the Atlantic have been recorded there, and for at least three of these species, the loggerhead (Caretta caretta), green turtle (Chelonia mydas), and hawksbill (Eretmochelys imbricata), the Sargasso Sea is vitally important.
Invites pretty much every species of big-game fish that fishermen dream about catching.
On shore, it’s a source of food for crabs, insects, and a myriad of tiny creatures, which in turn feed shorebirds and other coastal animals.
Important for collecting wind-blown sand (anchoring it to create dunes) and encouraging plant growth (due to the nutrients it contributes); long-term, restoring eroded beaches and, short-term, helping reduce wave and wind erosion on the beach!
Potential in the medical and pharmaceutical fields.
Serves as biofuel and land fill.
At times, unsightly (especially when accompanied by man-made marine debris).
Unpleasant smell, once it begins to decay.
Collects floating garbage that may pose a health or environmental risk.
Too much Sargassum can make it complicated for nesting sea turtles to arrive at shore; and for hatchlings to reach the ocean. Also, it’s more difficult to monitor turtle tracks.
It can adversely affect tourism.
Invasive species (e.g., Lionfish) can hitch a ride.
Decomposing in water, it can promote blooms of harmful bacteria /microbes resulting in serious skin irritation in humans.
When removed from the beach, heavy machinery tends to compact the sand (this can affect turtles nesting, e.g.) and remove both sand and nutrients from the shore, which can lead to beach erosion.
What can be done about it?
Businesses, organizations and local authorities have been coordinating to remove Sargassum from our beaches and shores, either manually, in wheelbarrows, or using different types of heavy machinery. Removing it remains necessary; nonetheless, as this cannot be done without unintended consequences that lead to beach erosion (e.g., removing Sargassum removes sand, heavy machinery compacts sand, etc.), making informed decisions about how to manage excess Sargassum is equally important – particularly because there is so much we have yet to understand.