93 
National Marine 
Spencer F. Baird /*"' V 
Fisheries Service 
Fishery Bulletin 
First U S. Commissioner U. W 
NOAA 
established in 1881 
of Fisheries and founder » Z- M 
of Fishery Bulletin 
Occurrence of pelagic Sargassum in waters of the 
U.S. Gulf of Mexico in response to weather-related 
hydrographic regimes associated with decadal and 
interannual variability in global climate 
Guillermo Sanchez-Rubio (contact author) 
Harriet Perry 
James S. Franks 
Donald R. Johnson 
Email address for contact author: guillermo.sanchez@usm.edu 
Center for Fisheries Research and Development 
Gulf Coast Research Laboratory 
School of Ocean Science and Technology 
The University of Southern Mississippi 
703 East Beach Drive 
Ocean Springs, MS 39564 
Abstract— Pelagic species of Sargas¬ 
sum, surface drifting macroalgae, 
occur in continental shelf and deep 
basin waters across the Gulf of Mex¬ 
ico (GOM). They often accumulate 
in mats and “windrows” to form a 
structured habitat that serves as a 
source of food and refuge for a di¬ 
verse assemblage of fish and inver¬ 
tebrates. Long-term temporal data 
on the distribution and abundance of 
Sargassum species in the GOM are 
lacking, but there is a time series 
of occurrence of those species across 
the U.S. GOM (USGOM) associated 
with ichthyoplankton surveys con¬ 
ducted by the Southeast Area Moni¬ 
toring and Assessment Program. The 
seasonal presence of Sargassum spe¬ 
cies in regions of the USGOM was 
compared under contrasting weath¬ 
er-related hydrographic regimes 
using nonparametric tests (Krus- 
kal-Wallis H test, Mann-Whitney 
U test, Wilcoxon signed rank test). 
Phases of the Atlantic Multidecadal 
Oscillation (AMO) and North Atlan¬ 
tic Oscillation (NAO) along with El 
Nino-Southern Oscillation (ENSO) 
events influenced seasonal presence 
of Sargassum species across the area 
of study. Occurrence of Sargassum 
species was highest under the cou¬ 
pled warm AMO and neutral NAO 
phases and cold ENSO events and 
was associated with physical and 
biological processes that transported 
the macroalgae to the USGOM and 
maintained them over time. 
Manuscript submitted 6 June 2017. 
Manuscript accepted 1 December 2017. 
Fish. Bull. 116:93-106 (2018). 
Online publication date: 2 January (2018). 
doi: 10.7755/FB.116.1.10 
The views and opinions expressed or 
implied in this article are those of the 
author (or authors) and do not necessarily 
reflect the position of the National 
Marine Fisheries Service, NOAA. 
Two holopelagic species of Sargas¬ 
sum, floating macroalgae (Phaeophy- 
ceae), co-occur in continental shelf 
and deep basin waters across the 
Gulf of Mexico (GOM): Sargassum 
natans and S. fluitans. These 2 spe¬ 
cies of macroalgae drift in surface 
waters (Deacon, 1942; Stoner, 1983) 
through the western Caribbean re¬ 
gion into the GOM and exit through 
the Florida Straits and up the east¬ 
ern seaboard of the United States in 
the Gulf Stream, and out into the 
Atlantic Ocean to the Sargasso Sea 
(Calder, 1995). The abundance and 
distribution of the 2 pelagic species 
of Sargassum in the Atlantic Ocean 
are highly variable over space and 
time (Gower and King, 2011; Gower 
et ah, 2013). Two historical quanti¬ 
tative studies of the abundance of 
pelagic Sargassum species were con¬ 
ducted in overlapping areas within 
the Sargasso Sea, the first between 
1933 and 1935 (Parr, 1939) and the 
second between 1977 and 1981 (Ston¬ 
er, 1983). No differences in overall 
abundance of these pelagic Sargas¬ 
sum species were found with these 
studies. In a more recent study, Huf- 
fard et al. (2014) examined tempo¬ 
ral and spatial variability of pelagic 
Sargassum community change over 
a 40-year period and noted that the 
distribution, abundance, or circula¬ 
tion patterns (or a combination of 
these variables) of pelagic Sargas¬ 
sum species in the Atlantic Ocean 
during 2010 and 2011 were highly 
anomalous compared with the 2003- 
2010 period. In the spring and sum¬ 
mer of 2011, Franks et al. (2011) and 
Johnson et al. (2013) reported that 
unprecedented amounts of pelagic 
Sargassum washed ashore along the 
Caribbean Islands, and satellite ob¬ 
servations pointed to waters north of 
the mouth of the Amazon River as a 
source region for the event (Gower et 
al., 2013). Johnson et al. (2013) ex¬ 
amined data from satellite- tracked 
current drifters during 2010 and 
2011 but were unable to connect the 
event to the central North Atlantic 
Ocean. These authors used an ar¬ 
chived numerical circulation model 
(Hybrid Coordinate Ocean Model) to 
backtrack pelagic Sargassum mac¬ 
roalgae to the North Equatorial Re¬ 
circulation Region (NERR). They sug- 
