Sanchez-Rubio et ai.: Occurrence of pelagic Sargassum in waters of the U.S. Gulf of Mexico 
103 
higher along the USGOM under the coupled AMOw/ 
NAOn phases. These wind conditions would facilitate 
retention of Sargassum mats within the study region 
and the transport of new mats of Sargassum species 
from the southern GOM. 
Operating within the decadal regimes are weather- 
related hydrographic characteristics imposed by in¬ 
terannual ENSO events. Higher occurrences of Sar¬ 
gassum species in the USGOM were associated with 
the ENSOc phase. Under ENSOc years, hydrographic 
characteristics in the NERR, Caribbean Sea, and GOM 
generally favor production, growth, and dispersion of 
the macroalgae. During ENSOc years, the ITCZ shifts 
south of its mean location (Saravanan and Chang, 
2000), creating a lower vertical shear over the regions 
of hurricane genesis and development of the tropical 
Atlantic Ocean (Gray, 1984; Goldenberg et al., 2001; 
Vitart and Anderson, 2001). The decrease in vertical 
shearing enhances the growth of prehurricane distur¬ 
bances in the Atlantic Ocean and increases the num¬ 
ber of hurricane landings on the continental United 
States (Eisner et ah, 2001). The turbulence associated 
with hurricanes would enhance fragmentation and 
dispersion of mats of pelagic Sargassum species along 
their paths of circulation. During the ENSOc years, 
the westward influence of south and southeast winds 
along the USGOM (Smith et al., 1998) and south wind 
momentum in spring (March-May) in the western US¬ 
GOM region (this study) were enhanced and therefore 
reduced the frequency of cold wind outbreaks, off-shelf 
water flow (Nowlin and Parker, 1974), and coastal up- 
welling (Dagg, 1988). These wind conditions would fa¬ 
vor retention of Sargassum mats in this region. High¬ 
est percentages of positive samples (Sargassum species 
present) occurred over the deep basin in the western 
region after ENSO events. Distributional results were 
consistent with traditional observations that the east¬ 
ern region is a zone of transport and the western re¬ 
gion is a zone of accumulation for Sargassum in the 
USGOM. 
Acknowledgments 
The authors would like to thank the anonymous re¬ 
viewers who provided constructive comments that 
strengthened the manuscript. This research was fund¬ 
ed by NMFS 2014 Marine Fisheries Initiative grant 
NA14NMF433022, for the project titled, “The effect of 
changing climate regimes on ephemeral nursery habi¬ 
tats: influence on selected reef fish populations in na¬ 
tional marine sanctuaries and habitat areas of particu¬ 
lar concern in the northern Gulf of Mexico.” 
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