Sargassum: Essential Habitat or Beach Nuisance, by Don Orth

A vacation at a beach resort near white sandy beaches and aqua blue waters was the plan.  However, the white sandy beaches and surf were covered with a thick mats of Sargassum, a brown macroalgae or 'seaweed.'  As I waded out beyond the floating seaweed, I could not see my feet in the sand, the water was that murky. The resort was along the Caribbean coastline known as the Riviera Maya, Mexico. This coastal zone is famous for its beaches and reef dependent recreation.  Tourism contributes 8.6% to the national GDP of Mexico and 45% of tourists choose the coastal zone as their destination (UNWTO 2016). Pristine beaches and associated recreational amenities are key attractions to coastal tourism worldwide (Onofrio and Nunes 2013). Hotel room prices are positively correlated to the beauty of the beach and recreation (Mendoza-González et al. 2018).  However,  'seaweed' is not part of the marketing plan for resorts.

 

Sargassum on the beach.

I know only a little about Sargassum, and that is about its role as offshore habitat for fish and invertebrates.  There are many species of Sargassum, bu  two species, Sargassum fluitans and Sargassum natans, dominate the floating mats. When trolling for pelagic fish the boat captain will seek out rafts of Sargassum, which attract numerous species (Dooley 1972). Some fishes will complete their entire lives in Sargassum, others use it for breeding, and others use it only for larval and juvenile habitats.  The Sargassumfish Histrio histrio is a frogfish (Antennariidae) that lives its entire life amidst the Sargassum (Pietsch and Grobecker 1987).  Sargassumfish are camouflaged with colors that change and weedy projections so that it blends into the floating seaweed. It dangles its esca as a fishing lure to attract small fish, shrimp and other invertebrates close enough to capture them.  

Floating raft of Sargassum photographed June 3, 2018 near Playa del Carmen, Mexico.

Sampling fishes in and around the floating Sargassum mats is a complicated process.  Therefore, I was not surprised by how few studies investigated the association of Sargassum and fishes. The studies I reviewed showed that small individuals from four or five fish families (Antenariidae, Carangidae, Monacanthidae, Syngnatidae, Tetraodontidae) typically made up over 90% of the sampled catch.  Depending the study duration and lcoation, between 36 to 110 fish species were identified (Dooley 1972; Bortone et al. 1977; Moser et al. 1998; Wells and Rooker 2004; Cassaza and Ross 2008; Moritz 2015).   Larger fishes, such as dolphinfishes, jacks, wahoo, and billfishes aggregated below the weedlines using the Sargassum for feeding habitat.  In addition to the fishes, Sargassum habitat provides feeding habitat for marine mammals, sea birds, and sea turtles (Cassaza and Ross 2008).

Fishes along Sargassum weed line near Cape Hatteras, North Carolina.  A. small planehead filefish; B. larger jacks below weed line; C. large predators, dolphinfish; D. schooling unicorn filefish; E. planehead filefish feeding on ctenophore;  and F. edge of Sagarssum weed line.  (Cassaza and Ross 2008).  

Realizing the importance of Sargassum to recruitment of many marine animals, NOAA approved a Sargassum Management Plan in 2003.  See the final rule here.  Development of this management plan was controversial over the interpretation of Sargassum as an essential habitat versus a harvestable product.  Larval and juvenile fishes of many species will be taken by Sargassum harvesters and effects of harvesting are unstudied. However, the current estimated harvest is miniscule compared with the estimated biomass of Sargassum.

Sargassum underwater near beach at Playa del Carmen, Mexico, photographed June 5, 2018. 

The Saragassum is widely distributed but the occurrence of Sargassum strandings on Caribbean beaches has become more common since 2011 (Franks et al. 2016).  Warming climate and changes in oceanic currents influence the spatial distribution and some researchers believe increases in nutrient loading may be stimulating an increase in Sargassum.  A forecast system based on satellite measurements shows promise for predicting the distribution and timing of Saragassum blooms, thereby providing localities with advance warnings of beaching events (Wang and Hu 2017).   

Locations of pelagic Sargassum and current vectors.  Franks et al. 2016. 

While, we were beach combing, my wife, Valerie, noted a small dead fish in the surf.  We began searching the recently beached Sargassum and found many others, all about 2-3 cm long.  She thought it was a pufferfish and my initial identification was incorrect.   After posting on All Fish Species Identification Group on Facebook, Pete Liptrot and Roy Hemdel identified it as Sharpose Puffer Canthigaster rostrata. 

Sharpnose Puffer Canthigaster rostrata and one puffer Sphoeroides sp. (bottom left) from beached Sargassum.

Sharpnose Puffer Canthigaster rostrata

Tourists in the region quickly learn that Sargassum is a common occurrence, but the quantity that reaches Caribbean beaches has increased.   The Caribbean Alliance for Sustainable Tourism and the Caribbean Hotel and Tourism Association created Sargassum: A Resource Guide for the Caribbean.   This guide examines possible impacts on beach tourism, uses of Sargassum, and management practices for beach resorts. Sargassum is an excellent medium for plant and crop growth and may become a new source of revenue.   Beach cleaning machines are available, but many resorts use manual removal in order to save costs and avoid issues with sea turtles. 

Gabriel raking Sargassum on beach.  Burying the Sargassum provides some relief to the problem.

Sargassum is a living renewable marine resource, a primary producer, and an essential habitat for many marine organisms, including highly migratory species.  For that reason, Sargassum should be managed and protected as essential habitat.  However, tourists expecting the picturesque sandy beaches will be dismayed to walk amidst the decaying Sargassum on the beaches. In the future, Caribbean beach resorts will need to adapt to changing climate conditions and the delivery of excessive amounts of Sargassum to pristine beaches. 

References

Casazzarro, T.L., and S.W. Ross. 2008. Fishes associated with pelagic Sargassum and open water lacking Sargassum in the Gulf Stream off North Carolina.  Fisheries Bulletin 106:348-363.

Dooley, J. K. 1972. Fishes associated with the pelagic Sargassum complex, with a discussion of the Sargassum community. Contributions in Marine Science 16:1–32.

Franks, J.S., D.R. Johnson, and D.S. Ko. 2016. Pelagic Sargassum in the tropical North Atlantic.   Gulf and Caribbean Research 27: SC6-11.

Mendoza-González, G., M.L. Martínez, R. Guevara, O. Pérez-Maqueo, M.C. Garza-Lagler, abd A. Howard, 2018. Towards a sustainable sun, sea, and sand tourism: The value of ocean view and proximity to the coast. Sustainability 10:1012-1026.

Moritz, T. 2015. Fishes of a stranded Sargassum meadow at Punta Cana, Dominican Republic. Bulletin of Fish Biology 15:141-146.

Moser, M.L., P.J. Auster, P.J., and J.B. Bichy. 1998. Effects of mat morphology on large Sargassum-associated fishes: observations from a remotely operated vehicle (ROV) and free-floating video cameras.    Environmental Biology of Fishes 51: 391-398.  

Onofri, L., and P.A.L.D Nunes. 2013. Beach ‘lovers’ and ‘greens’: A worldwide empirical analysis of coastal tourism. Ecological Economics 88:49–56.

Pietsch, T.W., and D.B. Grobecker.  1987. Frogfishes of the world. Stanford University Press, Stanford, CA, p 420

United Nations World Tourism Organization (UNWTO). Tourism Highlights. 2016. Available online: http://www.e-unwto.org/doi/pdf/10.18111/9789284418145 (accessed on 11 June 2018).

Wang, M. and  C. Hu. 2017. Predicting Sargassum blooms in the Caribbean Sea from MODIS observations. Geophysical Research Letters 44:3265-3273.

Wells, R.J.D., and J.R. Rooker. 2004. Spatial and temporal patterns of habitat use by fishes associated with Sargassum mats in the northwestern Gulf of Mexico.  Bulletin of Marine Sciences 74:81-99.