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
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.
Arrival in Carriacou, Grenada
November 15, 2017
Farley Miller, 2nd Assistant Scientist
In the words of Anna yesterday, “Here we are.” This evening, however, that phrase has a whole new meaning, and we aboard have the firmest sense of where we are yet. Land! Sighted early this morning as distant flickering lights 38 nm away, then rising out of the gloaming as the sun comes up and gives us colors to behold; then we are between two islands and in the lee and the smell of the land is overwhelming. Wet dirt, fresh wood smoke and an entirely new array of ocean smells not encountered in the open ocean.