Oceanography | Vol.28, No.3
RIP CURRENT | NEWS IN OCEANOGRAPHY
Recent Sargassum
Inundation Events in the Caribbean
Shipboard Observations Reveal Dominance of a Previously Rare Form
During June 2011, pelagic Sargassum began wash-
ing ashore along Caribbean, Gulf of Mexico, West
African, and Brazilian coastlines in unprecedented
quantities. Tourist beaches were covered by more
than a meter of seaweed. Economic impacts of
this Atlantic basin-scale inundation event drew
international media attention (Higgins, 2011). By
summer 2012, our shipboard observations sug-
gested the Caribbean portion of the event had
run its course. However, another similarly exten-
sive Sargassum inundation was underway by April
2014, persisting through 2015 (MercoPress, 2015).
Did the invading pelagic Sargassum drift out
of the Sargasso Sea, a vast region bounded by the
currents of the North Atlantic gyre (Smetacek and
Zingone, 2013)? Alternatively, is its source the
North Equatorial Recirculation Region (NERR),
as suggested by satellite- derived observations of
Sargassum mats (Gower et al., 2013) and hind-
cast models of Sargassum landfalls (Johnson
et al., 2013)? Our recent net sampling indicates
that the invading Sargassum did not come from
the Sargasso Sea.
In late November 2014, Sea Education
Association’s (SEA’s) SSV Corwith Cramer departed
the Canary Islands. We sailed across the eastern
Sargasso Sea without a sighting, but on day 15,
after heading south into the tropics, we were sur-
rounded by Sargassum. For the next three weeks,
twice-daily surface net tows contained more
Sargassum than ever recorded by SEA voyages.
We noticed the seaweed looked different from the
Sargassum fluitans or S. natans with which we were
familiar from 20 years of sailing in the Sargasso
Sea, the Caribbean, and Florida Straits (Figure 1a).
Most resources assert pelagic Sargassum is com-
posed of two species, S. fluitans and S. natans.
However, each species exhibits a diversity of
FIGURE 1. Characteristics of three pelagic Sargassum forms (left to right:
S. natans I Parr, S. fluitans III Parr, and S. natans VIII Parr) collected during the
2014/2015 Caribbean inundation event. (a) Fronds showing arrangement of stem,
blades, and bladders. (b) Section of stem highlighting presence/absence of thorns.
Bladders and blades removed. (c) Bladders highlighting presence/absence of
spines. Bladder stalk is directed downward in each photo. (d) Mean and standard
error for length (mm), width (mm), and length/width ratio of blades. *Hydroid colonies
are often present on Sargassum and can be mistaken for spines or thorns.
By Jeffrey M. Schell, Deborah S. Goodwin,
and Amy N.S. Siuda