Pelagic Sargassum is a macroalgae that drifts at the ocean surface in small clumps or extensive mats, creating a unique and ecologically-significant marine ecosystem. Two species are common in the North Atlantic, S. natans and S. fluitans. Serving as a food source, nursery for juveniles, spawning ground, and/or protective habitat, Sargassum mats support diversities of invertebrates, fish, turtles, and seabirds at various points of their life cycle.
For more than 40 years, SEA has been documenting Sargassum species, abundance, and distribution along repeated cruise tracks through the Sargasso Sea, Caribbean Sea, and Gulf of Mexico. More recent investigations include associated epibiont and mobile fauna communities, genetic diversity, seasonal and interannual variability, and unique Caribbean inundation events. SEA Semester students also contribute to marine spatial planning and policy initiatives working to conserve the Sargasso Sea ecosystem.
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. At SEA, we are interested in understanding the factors that affect the diversity and composition of the associated Sargassum community, such as host species, geographic location, clump size, and clump aggregation/dispersion pattern. Both visual/microscope-aided identification and genetic population analyses are utilized to characterize Sargassum communities.
Selected Community of organisms papers and publications
SEA’s 40-year plankton net tow data set indicates that distinct seasonal and interannual distribution patterns exist for each Sargassum species. S. natans is most commonly found in the central Sargasso Sea while S. fluitans is more abundant in the Gulf Stream, North Equatorial Current, and Caribbean Sea. Our field observations complement satellite detection methods by providing species identification and finer spatial resolution.
Selected Distribution patterns papers and publications
During 2011-2012 and 2014-2015, 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 have discovered that the Sargassum inundating the Caribbean in 2014-2015 is a previously rare form of S. natans, potentially originating in the equatorial 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
Sargassum natans and S. fluitans each exhibit a diversity of morphological forms that have distinct but overlapping ranges; correct identification in the field is critical for understanding species dynamics and resolving questions of Sargassum connectivity among geographic regions. Presence or absence of thorns on the stem distinguishes between species: S. natans has smooth stems while S. fluitans has thorns. Within a species, leaf and bladder attributes can differ widely among forms. SEA uses both dip nets and surface neuston tows to collect Sargassum, then makes careful visual observations to determine the species and form.
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.