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What is sargassum?
Sargassum is a brown marine alga (seaweed) that is found throughout the oceans of the World but generally associated with the Sargasso Sea (in the North Atlantic). Most species are attached to the seafloor. However, there are two species, Sargassum natans and Sargassum fluitans that are never attached but instead are free floating for their entire life cycle. They form mats or rows of seaweed parallel to prevailing wind direction and are carried by currents (Franks et al. 2011) and are those species washing ashore in the Caribbean currently.
Since 2011, the Caribbean region has been experiencing year-to-year variation of an influx of these two species of pelagic sargassum with 2018 having the highest recorded levels, bringing with it a diversity of social, ecological and economic concerns but also great opportunities and economic potential.
Where is it coming from?
By using a combination of ocean models, satellite trackers, and examining high resolution satellite images, scientists have back - tracked the movement of sargassum from the 2011 stranding locations. They have established that the recent influxes to the Caribbean Sea and along the coast of West Africa are related to massive blooms occurring in the equatorial area of the Atlantic called the North Equatorial Recirculation Region (NERR), which is not directly associated with the Sargasso Sea.
What causes the influx of sargassum in the Caribbean?
A combination of factors are believed to be contributing to these large quantities of sargassum including warming ocean temperatures and increased discharge of nutrients (such as nitrogen and phosphorus) from land based sources (e.g. agricultural run off, wastewater) and oil spills into the marine environment. Fluctuations in currents and climate are allowing build up and release of large quantities which then travel north westwards up into the Caribbean Sea with the North Brazil and Guiana currents.
Will the sargassum influx occur every year?
Predictions from the University of South Florida Optical Oceanography Lab believe that 2019 will likely be another major bloom year if the current Central West Atlantic condition continues. [See Wang and Hu, 2018:https://optics.marine.usf.edu/projects/SaWS/pdf/Sargassum_outlook_2018_bulletin12_USF.pdf]. However it is hard to know whether this will continue every year. Variability due to seawater temperatures and nutrient availability and differences in strength and direction of surface currents and winds affect the growth rate and trajectory as well as frequency and location of strandings.
Ecological Value of Sargassum
There is a diversity and abundance of species of fish and marine invertebrates that depend on the ecosystem created by the floating sargassum mats for shelter and food. They also serve as important feeding grounds for commercially important species such as dolphin fish (mahi mahi) and tuna, act as spawning areas for flying fish, nursery grounds for endangered sea turtles and foraging areas for seabirds (Hinds et al. 2016). Once ashore, sargassum nourishes beaches, stabilizes the shoreline and acts as natural fertilizer for beach vegetation.
Negative impacts of sargassum
Perceived as a nuisance by the majority, sargassum has had negative impacts on marine resources, fisheries, shorelines and tourism. Fishing vessels have had to deal with entangled gear and blocked propellers while some fisherfolk have limited access to boats in bays and have reported a decline in flying fish catches over the past few years threatening their livelihoods. Although there has been an increase in catch of juvenile dolphin fish associated with the sargassum mats off Barbados, this could have negative implications for the future of the stock and shows the need for sustainable management of this resource.
Sargassum brown tides in the nearshore contribute to reduction in light, oxygen and pH in some studied environments which has implications for nearshore seagrasses, corals and other marine life.
When the seaweed builds up onshore, it is not only visually unappealing mixed with marine and beach littler such as plastics but it starts to decompose producing hydrogen sulfide gas (rotten egg smell). This gas is harmful to most marine animals and can have potential human health concerns under prolonged exposure to high concentrations.
Need for Sustainable Management
There is a need for proactive and collaborative management as there is no one size fits all solution to management of sargassum. I have been sent videos of different kinds of machinery and booms many times recently and been asked why aren’t we using it here? It is not as simple as that. It depends on a combination of factors such as the coast, currents, waves, biomass, accessibility of shoreline, ecological, fishing and tourism impacts.
The most sustainable practice is to let nature run her course in areas where there are small quantities of sargassum or at inaccessible or low tourist locations. Nearshore in water collection and harvest and onshore cleaning should be prioritized while leaving small amounts of sargassum behind. When the volume is low, manual (hand) raking is best as it reduces disturbance to sea turtle nests and beach erosion which can be worsened by heavy machinery. In water collection very close to shore (in low surf, swell and current areas) is preferable where permitted (some countries require harvest permits) taking into consideration any sea turtle hatchlings or other marine life that may be hidden or trapped underneath. Before cleaning a beach, check for marine life in sargassum or contact the Barbados Sea Turtle Project to determine sea turtle nesting areas.
Source: Doyle, Franks and Oxenford. https://www.gcfi.org/wp-content/uploads/2018/05/ONLINE-Sargassum.png
So now that the sargassum has been collected, what can be done with it?
Sargassum as a resource – the new Caribbean Gold?
There are many potential opportunities associated with sargassum – from the creation of value added products, employment and development of the marine biotechnology industry as we continue to move towards a blue economy.
Sargassum can be buried further up the beach on wider beaches to act as fertilizer and for beach nourishment. However, it is an amazing resource both when floating at sea and now that is has landed on our doorstep. It has many value added uses such as natural fertilizer, plant tonic, mulch, compost, pest control, biofuel/biogas, chipboard, fish food, chemical compounds for pharmaceuticals and personal care.
It must be noted that the species of pelagic sargassum involved in the influx are different from those grown as sea moss in the Caribbean and a favourite in some drinks in the region. Human consumption of these species is not recommended until further analysis is conducted.
How Can You Help
Check out the Barbados Sargassum Monitoring and Management page on Facebook (https://www.facebook.com/groups/1898646553512261/permalink/2228470410529872/). Take photos and videos and share with location and date. Keep an eye out for any organisms or entangled sea turtles or marine mammals and call the Barbados Sea Turtle Project 24 hour hotline at 230-0142 if you do! Stay informed by The Ministry of Maritime Affairs and the Blue Economy as they continue to share information on the sargassum issue including any need for volunteers for clean up and harvest efforts.
Although there are still many uncertainties surrounding the influx of pelagic sargassum, what is known is that it is currently here and there is opportunity associated with it. There needs to be a balance between the importance of sargassum for natural processes, the potential for industry and the negative impacts on fisheries, locals and tourism.
As the responsible ministry continues to communicate, engage with key stakeholders and public as well as create public-private partnerships, how do we continue to move forward as a country and turn this problem into profit?
Nikola Simpson is a marine biologist and coastal and environmental resource manager.
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