102 
Fishery Bulletin 11 6(1) 
Table 5 
Monthly mean values, with 95% confidence intervals, of environmental factors from the North Equatorial Recirculation Re¬ 
gion (NERR) and Gulf of Mexico (GOM) during the coupling of phases of the Atlantic Multidecadal Oscillation (AMO) and 
North Atlantic Oscillation (NAO). The numbers in parentheses and n represent the total number of values or features that 
were compared; P-values are those given by the Mann-Whitney U test for the analysis of values between AMO and NAO 
phases. AMM=Atlantic Meridional Mode. 
Variables 
Region 
Month 
Wind 
direction 
p 
Cold AMO, positive 
NAO phases 
Warm AMO, negative 
NAO phases 
AMM 
NERR 
Aug-Mar 
0 
-1.56 ±0.81 (13) 
1.52 ±0.85 (15) 
Wind momentum 
Western GOM 
Sep-Nov 
NW 
0.031 
4.27 ±2.50 (12) 
7.65 ±3.19(14) 
Dec-Feb 
SE 
0.005 
46.61 ±9.37 (15) 
67.64 ±22.89 (10) 
Mar-May 
SE 
0.030 
82.66 ±21.59 (13) 
109.80 ±34.02 (12) 
Central GOM 
Sep-Nov 
S 
0.017 
6.78 ±1.94 (12) 
10.95 ±3.08 (15) 
Jun-Aug 
W 
0.022 
1.03 ±0.48 (7) 
1.89 ±0.53 (15) 
Eastern GOM 
Sep-Nov 
S 
0.010 
4.18 ±1.74 (9) 
9.76 ±3.77 (13) 
Sep-Nov 
sw 
0.003 
1.05 ±0.42 (8) 
4.23 ±1.65 (12) 
Hurricanes 
GOM 
Jun-Nov 
n=23 
77=38 
NERR 
Jun-Nov 
a 
n 
CO 
71 = 12 
Loop Current eddies 
GOM 
Jan-Dec 
71=17 
77=23 
Amazon River discharge 
NERR 
Apr-Aug 
Relow average (7/13) 
Above average (14/19) 
ence of hurricanes on abundance of Sargassum species 
is largely undocumented, but biotic characteristics of 
the macroalgae (such as fragmentation) and its posi¬ 
tion in the water column (i.e., in surface waters) would 
cause the species to be responsive to physical processes 
associated with the passing of tropical storms. Water 
turbulence associated with hurricanes may positively 
affect abundances through increased dispersion, trans¬ 
port, upwelling, and fragmentation. Pelagic Sargassum 
species reproduce asexually by fragmentation (Fritsch, 
1965; Round, 1981; Awasthi, 2007; Rogers, 2011) when 
younger parts of the thallus separate from the older 
parts or when there is physical injury to any part 
of the plant (Hanisak and Samuel, 1987). Separated 
parts of the plant have the potential to mature into 
fully formed organisms (Hanisak and Samuel, 1987). 
In addition to fragmentation of individual plants, mats 
of Sargassum species could be broken apart and more 
widely dispersed. 
For species of Sargassum , the eastern region of the 
GOM is generally regarded as a zone of transport that 
serves to move the macroalgae into the GOM via the 
Yucatan Current and out via the Florida Current. The 
western zone is considered an area of residence and 
growth where LC spin-off eddies decay and deposit Sar¬ 
gassum macroalgae. Circulation in the eastern GOM is 
dominated by the LC, a fast-moving current that can 
reach maximum flow speeds of 1.5 to 1.8 m/s (Gordon, 
1967). Degree of northward penetration of the LC into 
the GOM varies as does the time and number of eddies 
shed. Eddies are usually mesoscale circulation features 
but can measure 200-400 km in diameter and extend 
to a depth of 1000 m (Mooers, 1998). They are shed 
randomly every 3 to 17 months (Sturges and Leben, 
2000) and the majority of them drift to the western 
GOM where they may persist for weeks (Oey et ah, 
2005). Species of Sargassum can be readily entrained 
in fronts formed by convergent surface currents associ¬ 
ated with large spin-off eddies that appear in satellite 
images (Gower et al., 2006) as long curving lines. The 
balance of forces in eddy motions favors entrapment of 
Sargassum around the periphery of anticyclonic (coun¬ 
terclockwise in the Northern Hemisphere) eddies and 
in the center of cyclonic eddies owing to sea-surface 
height gradients and frictional processes. More com¬ 
plex patterns, however, are formed by stepwise con¬ 
vergent fronts across the surface of mesoscale eddies 
and associated lines of Sargassum (Zhong et al., 2012) 
within both cyclonic and anticyclonic eddies. 
The higher numbers of eddies shed under the cou¬ 
pled AMOw/NAOn phases and the relatively long pe¬ 
riod associated with eddy decay may have contributed 
to the greater incidence of Sargassum species observed 
in the western USGOM in our study. Regional occur¬ 
rence was 8.46% in the western USGOM and 6.47% in 
the eastern USGOM under the coupled AMOw/NAOn 
phases and 3.41% and 2.69% in the western and east¬ 
ern regions under the coupled AMOc/NAOp phases, 
respectively. Highest percentages of positive samples 
(Sargassum species present) occurred over the deep 
basin in the western region irrespective of climate re¬ 
gime: coupled AMOw/NAOn phases (10.2%), coupled 
AMOc/NAOp phases (7.28%). Gower et al. (2006), using 
satellite imagery, observed that most Sargassum mac¬ 
roalgae were found in the western GOM and noted that 
in areas where surface waters circulate in slowly rotat¬ 
ing gyres, the macroalgae would be expected to accu¬ 
mulate. Wind momentum, a measure of the transport 
of surface water, also favored retention of species of 
Sargassum. South and southeast wind momentum was 
