Pelagic Sargassum is a macroalgae that drifts at the ocean surface, creating a unique and ecologically-significant marine ecosystem. Accumulations of Sargassum, whether they be isolated clumps or aggregated long windrows or mats covering 100’s of square meters, serve as a food source, nursery for juveniles, spawning ground and/or protective habitat for diverse invertebrate, fish, turtle and seabird species at various points of their life cycle.
For over 45 years, SEA has been documenting Sargassum species, abundance and distribution along repeated cruise tracks through the Sargasso Sea, Caribbean Sea and Gulf of Mexico. Recent investigations include the associated epibiont and mobile fauna communities, seasonal and interannual variability in distribution, and extraordinary Caribbean inundation events. SEA Semester students, faculty and collaborators use a variety of tools to examine Sargassum itself and its hosted organisms, from field observations to morphological metrics to molecular analyses of diversity. Marine spatial planning and policy initiatives working to conserve the Sargasso Sea ecosystem also benefit from SEA students’ contributions and creative ideas. Seeking to share Sargassum research beyond the scientific community, SEA faculty scientists have taken part in many outreach events and were featured on the Meet the Ocean podcast.
Community of organisms
A uniquely adapted pseudo-benthic community of organisms lives among the dense vegetation of each pelagic Sargassum clump, including common epifauna such as hydroids and mobile fauna such as shrimp, snails and crabs. SEA scientists and students seek to understand factors affecting the diversity and composition of this community, such as host species, genetic connectivity, geographic location, clump size and clump aggregation/dispersion pattern. Both visual/microscope-aided identification and genetic population analyses are utilized. Preliminary studies reveal that each Sargassum species and morphological form harbors a unique assemblage of organisms. Further, emerging SEA research suggests that the genetic structure of epibiont species could help explain questions of Sargassum origin and distribution.
SEA faculty and collaborators: Jeff Schell (SEA), Deb Goodwin (SEA), Kerry Whittaker (SEA), Amy Siuda (Eckerd College), Annette Govindarajan (WHOI), Lindsay Martin, Madelyn Taylor
Selected Community of organisms papers and publications
SEA’s 45-year plankton net tow data set indicates that distinct seasonal and interannual distribution patterns exist for each Sargassum species and morphological form. S. natans I is most commonly found in the central Sargasso Sea while S. natans VIII is often seen in the tropical Atlantic and Caribbean, and S. natans II is most frequent in the western Caribbean. S. fluitans III is broadly distributed across the Gulf Stream, North Equatorial Current, and Caribbean in addition to the Sargasso Sea. SEA field observations complement satellite detection methods by providing species identification and finer spatial resolution.
SEA faculty and collaborators: Jeff Schell (SEA), Deb Goodwin (SEA), Amy Siuda (Eckerd College)
Selected Distribution patterns papers and publications
During 2011-2012, 2014-2015, and again in 2018, pelagic Sargassum washed ashore in unprecedented quantities throughout the tropical Atlantic, including on many Caribbean islands. Once-pristine tourist beaches were covered by meters of stranded seaweed. Researchers at SEA discovered the Sargassum that inundated the Caribbean in 2014-2015 was the previously-rare form S. natans VIII, originating in the northern tropical Atlantic region. Inundation events have ecological consequences at multiple scales, such as impacts to Sargassum mobile fauna communities, dependent fisheries and iconic species, and coastal ecosystem function.
Selected Inundation events papers and publications
Historically, only two species of pelagic Sargassum were recognized in the North Atlantic: S. natans and S. fluitans. However, field collections via dip net and surface net tow combined with morphometric and genetic analyses by SEA scientists have identified distinct forms of both species. Presence or absence of thorns on the stem distinguishes between species: S. natans has smooth stems while S. fluitans has thorns. Within a species, blade and float attributes differ widely among forms – S. natans I has long, narrow blades and floats frequently adorned with an apical spine whereas S. natans VIII has long, wide blades with floats that rarely exhibit a spine. Preliminary observations indicate that a third form, S. natans II, can be identified by blade width between that of S. natans I and S. natans VIII and floats adorned with a spine. S. fluitans III has short, compact blades and no spines on the floats. Because Sargassum forms have discrete but overlapping ranges, correct field identification through visual study is critical for addressing questions of distribution, evolution, and connectivity between geographic regions. Genetic tools developed by SEA researchers distinguish morphotypes and further resolve phylogenetic relationships among Sargassum specimens.
SEA faculty and collaborators: Jeff Schell (SEA), Deb Goodwin (SEA), Kerry Whittaker (SEA), Amy Siuda (Eckerd College)
Selected Taxonomy papers and publications
Hu, C., B. Murch, B. B. Barnes, M. Wang, J.-P. Maréchal, J. Franks, D. Johnson, B. Lapointe, D. S. Goodwin*, J. M. Schell* and A. N. S. Siuda^, 2016. Sargassum Watch warns of incoming seaweed. EOS Earth and Space Science News 97, 10-15.
Stoner*, A. W. and H. S. Greening, 1984. Geographic variation in the macrofaunal associates of pelagic Sargassum. Mar. Ecol. Prog. Ser. 20, 185-192. doi: 10.3354/meps020185
Butler, J. N. and A. W. Stoner*, 1984. Pelagic Sargassum: has its biomass changed in the last 50 years? Deep-Sea Res. Part A 31, 1259-1264. doi: 10.1016/0198-0149(84)90061-X
Stoner*, A. W., 1983. Pelagic Sargassum: Evidence for a major decrease in biomass. Deep-Sea Res. Part A 30, 469-474. doi: 10.1016/0198-0149(83)90079-1
Selected student research
Olson, E. and E. Tonkin, 2015. A Genetic and Morphological Analysis of Atlantic Sargassum. Unpublished student research paper, Class C-259, Sea Education Association, Woods Hole, MA.
Tyrrell, S., 2015. Sargassum Species Distribution in the North Atlantic. Unpublished student research paper, Class C-257, Sea Education Association, Woods Hole, MA.
Wooster, S., 2015. Sargassum Community Comparison Between Isolated Clumps and Windrows. Unpublished student research paper, Class C-257, Sea Education Association, Woods Hole, MA.
Disbrow, M., 2015. Community Composition on Three Sargassum Morphological Forms. Unpublished student research paper, Class C-257, Sea Education Association, Woods Hole, MA.
Matthews, T., B. Stockdale and M. Howard, 2013. Zoogeography of Floating Sargassum in the Caribbean. Unpublished student research paper, Class C-250, Sea Education Association, Woods Hole, MA.
Bishop, E. and A. Mackie-Donnelly, 2013. Investigating Sargassum's Distribution Pattern: A Pelagic Seaweed's Relation to Plastic and Epifauna in the North Atlantic. Unpublished student research paper, Class C-249, Sea Education Association, Woods Hole, MA.
Mygas, S. and M. Opela, 2012. Age and Distribution of Sargassum natans and S. fluitans in the North Atlantic. Unpublished student research paper, Class C-243, Sea Education Association, Woods Hole, MA.
Urban, E., 2012. Sessile Epibiont Variety and Abundance as a Method of Correlating Sargassum Age and Geographic Location in the Sargasso Sea. Unpublished student research paper, Class C-243, Sea Education Association, Woods Hole, MA.
Pinheiro, V., 2012. The Role of Sargassum fluitans and S. natans in the Ontogeny of Anguillid Leptocephali in the Sargasso Sea. Unpublished student research paper, Class C-240, Sea Education Association, Woods Hole, MA.
Wylie, B. and K. Gonzalez, 2010. Long-term Trends and Distributions of Holoplanktonic Sargassum in the Caribbean Sea from 1981 to 2010. Unpublished student research paper, Class C-232, Sea Education Association, Woods Hole, MA.
Sargent, S., 2010. Camouflage in Sargassum Habitat Choice in Sargassum Shrimp and Crabs in the Caribbean Sea. Unpublished student research paper, Class C-232, Sea Education Association, Woods Hole, MA.
Schell, J.*, 2014. Drifting oases of life in the Sargasso Sea: fish, fishing and fisheries. Cataumet Schoolhouse Summer Series, Cataumet, MA.
Goodwin, D. S.*, J. S. Schell* and A. N. S. Suida*, 2014. Sargassum natans and S. fluitans exhibit geographically distinct distributions in a 20-year neuston net dataset from the western North Atlantic. Ocean Sciences Meeting, Honolulu, HI.
Siuda, A.* and D. Goodwin*, 2013. Sargassum sp. distributions in the western North Atlantic - implications for conservation and management. BioNES Meeting, Bristol, RI.
* SEA faculty and staff
^ SEA Semester alumnus
Deploying the Neuston Net
February 28, 2019
With nearly 50 years of surface neuston tow data, SEA’s archives offer the unique opportunity to examine biological response to global change. SEA Semester leverages the opportunities presented by its remote, open ocean cruise tracks and repeated annual sampling to build valuable datasets in poorly studied areas of the world.
O-fish-ially deep into the Sargasso Sea
May 03, 2018
Helena McMonagle, Lab Hand
As our second week comes to a close, I already feel like our community aboard Mama Cramer is gelling. You can get used to almost anything: flushing the head (aka toilet) with a hand pump, showering about once every three days, and eating on gimbled tables that continuously tilt to counteract the ship’s rocking.
May 02, 2018
Jenny Renee, B watch, University of Washington
I’m happy to report Sargy Success from the Sargassum group (Alena, Dani and I)! Sargy, as we have affectionately started calling Sargassum - ok, maybe it’s just me - is a seaweed that spends its entire life floating in the open ocean. This floating Sargassum supports a diverse community of mobile and sessile fauna, small islands of diversity within a blue desert.
A week at sea & the Great Pin Rail Chase!
April 27, 2018
Nate Lammers, C Watch, 3rd Mate
A week ago, at 12:13 EDT, we cast off our last line in Nassau, Bahamas and motored out to sea. It’s hard to believe we have officially been underway for a week! The days are flying by and just seem to blend together. With the revolving 6 on, 12 off watch schedule we are constantly changing our work and sleep schedule which really makes it hard to keep track of the time.
April 20, 2018
Carly Carter, A Watch, Longwood University, Cormier Honors College
TGIF! Well, not so much on the Cramer, especially with our work just beginning! We spent the morning doing our last bit of orientation and getting the ship ready before shipping out to begin our voyage. We have had so much information thrown at us the past few days that I don’t know what stuck and what didn’t, so being underway will sure test our knowledge. We have a lot of new skills to learn, and a lot of old skills to re-learn.
A Sargassum crab (Portunis sayi), camouflaged among the blades and floats of a Sargassum clump.
The tools of Sargassum clump analysis: color chart, ruler, spring scale, magnifying glass, and datasheet.
When conditions permit, Sargassum and associated fauna may be observed and collected using the ship’s small boat.
Each collected clump of Sargassum is identified to species, examined for epibionts, and weighed.
Surface neuston net tows, conducted alongside the ship, often catch Sargassum clumps - on the frame as well as in the net.
Proper field identification is critical; in-class reviews highlighting key morphological features are held on every Atlantic cruise.
An in-water view of a Sargassum clump in the Florida Keys.
Sample processing includes collection, counting and identification of every associated organism, such as shrimp, crabs, and fish.
The SSV Corwith Cramer sails near a large Sargassum mat in the tropical North Atlantic.
Dip net sampling for Sargassum on a sunny afternoon. This method allows for collection of individual clumps.
Sargassum natans-1, a morphological form characterized by smooth stems, narrow blades, and spines or projections from the floats.
Sargassum fluitans ssp., a morphological form characterized by thorny stems, broad blades, and floats without spines.
Sargassum natans-VIII, a morphological form characterized by smooth stems, broad blades, and floats only very rarely with spines.
2015 SEA Semester: Marine Biodiversity and Conservation program student research focused on Sargassum forms.