PRESS RELEASE – Massive quantities of Sargassum, a distinctive brown seaweed, have flooded Caribbean shores in recent years, setting off local concerns about economic impacts on fishing and tourism.
The country of Trinidad has even declared these so-called inundation events to be a natural disaster. But little is understood about the ecological implications of these Sargassum invasions or how they should be managed. New research published by Sea Education Association, a leading ocean education and research institution based in Woods Hole, Massachusetts, provides first-hand observations in support of these questions.
In the September 2015 issue of the journal Oceanography, Drs. Jeffrey Schell, Amy Siuda, and Deb Goodwin, all SEA Semester® oceanography faculty members, report the results of shipboard sampling during and after the latest Caribbean inundation event in 2014 and 2015. Major findings include:
Previously rare type: According to most existing resources, open-ocean forms of Sargassum consist of two main species: S. fluitans and S. natans, distinguished by their differing stems, blades and bladders. Decades of SEA sampling had indicated that two Sargassum forms within those species, S. natans I Parr and S. fluitans Parr were the most common in the North Atlantic, Caribbean Sea, and Gulf of Mexico.
However, in their latest fieldwork, SEA researchers found that a third form — S. natans VIII Parr — dominated the Western Tropical Atlantic, Eastern Caribbean, and Antilles. This abundance was significant because in the past this form rarely appeared in these areas.
Unexpected source: Based on the abundance and forms of Sargassum found through their net sampling, SEA researchers concluded that the Sargasso Sea, a vast region of the North Atlantic Ocean long known for hosting the biologically-important seaweed, has no connection to the recent Caribbean inundation events.
While S. natans VIII dominated the Caribbean samples, a different type of seaweed, S. natans I, dominated the South Sargasso Sea. These findings support the theory proposed by other scientists that the Sargassum washing ashore on Caribbean beaches is coming from another location, such as a more southern portion of the Atlantic known as the North Equatorial Recirculation Region.
Unprecedented amounts: SEA research found that the average concentration of all Sargassum forms combined was 10 times greater in samples collected during autumn 2014 than those analyzed during a previous 2011-12 inundation event—and a whopping 300 times greater than that of any other autumn over the last two decades of SEA research. Therefore, SEA researchers concluded that the 2014-15 Caribbean inundation event was truly unprecedented.
Data for this study was collected by SEA faculty, crew, and SEA Semester® undergraduate students on board the institution’s 135-foot tall sailing ship, the SSV Corwith Cramer, from November 2014 to May 2015. Cruises began in the Canary Islands, traversed the Sargasso Sea and Western Tropical Atlantic to the Lesser Antilles, and then sailed the Eastern Caribbean before heading to New England.
SEA researchers have been studying Sargassum in the field for about four decades in an effort to understand more fully the ecosystems that rely upon this floating seaweed. SEA’s datasets are extraordinary in that they represent the only long-term quantitative record of Sargassum abundance before and during these Caribbean inundation events.
The authors of this study note: “pressing future questions include the ecological impacts of inundation events on coral reefs, sea turtles and fisheries. Continued Sargassum field observations are essential to these efforts.”