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
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.
Counting Down to Bermuda
May 05, 2017
Megs Malpani, A Watch, Brown University
Today we got hit with some winds (Force 5-6), a stark difference from the calm of yesterday. Though I’m still running off the high of going aloft yesterday (truly the most incredible view in the world – definitely a trip highlight), I couldn’t imagine climbing the mast in these waves, and the winds are only supposed to get stronger. That being said, I don’t have a lot of pictures so I’m just going to share this cool one from yesterday!
From the Smallest to the Tallest
May 04, 2017
Maggie Schultz, B Watch, Mount Holyoke College
Today began with (vegan) pancakes from our amazing steward Sabrina. She has been feeding us non-stop with gourmet meals and snacks six times a day, there is more food here than I’ve ever seen in my life. After an amazing breakfast, my watch (B-watch) was ready to take the deck. Half of us went to tend the sails and ship while the others, Anna and myself went to lab with our scientist leader Grayson. When I walked into lab, there were pantyhose filled with styrofoam cups we had decorated, hanging around the lab disco ball.
Day in the Life of a Galley Steward
May 01, 2017
Ridge Pierce, A Watch, Roger Williams University
We reached our 1,000th cumulative mile of our journey during early dawn this morning while the spray was whipping over the bow and the only light on deck was from the stars. We were taking a slight diversion South through the South Sargasso Sea in hopes of obtaining more samples of Sargassum and possibly the form we have not found much of on this voyage:
Cramer Gybes and Students’ First Dip Net!
April 21, 2017
Paige Petit, A Watch, College of the Holy Cross
After spending a few hours feeling nauseous at every trip below decks yesterday, it is amazing that I was able to spend most of my 6 hour watch as the dish assistant today in the galley! It feels great to (hopefully) be acquiring some sea legs, of course attributing most credit to medicine, a full belly, and a hydrated body. As a “newbie” aboard the Cramer, the crew is nothing but kind and positive.