Over the past few weeks, sargassum has been a hot topic that has floated into almost every conversation that I have had – with other biologists, researchers and fisherfolk to economists and entrepreneurs, school children, the random man behind me in the bank line, on the side of the road in town and even with guests at a wedding.
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 currently washing ashore in the Caribbean.
Since 2011, the Caribbean region has been experiencing year-to-year variation of an influx of these two species of pelagic sargassum with 2015 having the highest recorded levels (until now). We are in the middle of what appears to be the largest influx so far, 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 the 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 the sargassum influx will continue into the Caribbean until at least August 2018 (Wang and Hu, 2017). 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 fish species 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 a 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 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 the 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.
Due to sargassum brown tides in the near-shore, there has been a reduction in light, oxygen and ph in some studied environments which has implications for near-shore sea-grasses, corals and other marine life. As was seen a few weeks ago, species of turtles, dolphins and other marine life died on the East Coast of Barbados as a result of lack of oxygen, dehydration and stress from becoming trapped in the sargassum.
When the seaweed builds up onshore, it is not only visually unappealing mixed with marine and beach litter such as plastics, but it starts to decompose producing hydrogen sulphide 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.
Tourism, which has already taken a big blow this season with sewage associated issues, has also been negatively impacted by sargassum. So what’s next?
Need for Sustainable Management
There is a need for proactive and collaborative management as there is no one-size- fits-all solution to the management of sargassum. I have been sent videos of different kinds of machinery and booms many times recently and been asked why we aren’t 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 the shoreline, ecological, fishing and tourism impacts.
The most sustainable practice is to let nature do her thing 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.
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 – the creation of value-added products, employment and the 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 it is has landed on our doorstep. It has many value added uses such as a 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 two local Facebook pages that are increasing public information, education and awareness: National Sargassum Clean Up – Barbados 2018 and Sargassum Monitoring Network Barbados. Also stay informed by the Minister of Maritime Affairs and the Blue Economy, Kirk Humphrey and his team as they continue to share information on the sargassum issue including the need for volunteers for clean up and harvest efforts.
Nikola Simpson is a marine biologist and environmental consultant that is passionate about spreading awareness on the environment and oceans that support us!