Sanchez-Rubio et al.: Occurrence of pelagic Sargassum in waters of the U S. Gulf of Mexico 
99 
Table 2 
Mean summer (May-July) occurrence, with 95% confidence intervals, of pelagic species of Sargassum 
in waters over the continental shelf and deep basin of the U.S. Gulf of Mexico and the western and 
eastern regions during phases of the coupling of the Atlantic Multidecadal Oscillation (AMO) and 
North Atlantic Oscillation (NAO) from 1982 through 2012. Occurrence represents the percentage of 
ichthyoplankton samples associated with pelagic Sargassum. ;?=the total number of square degree 
areas (1 degree latitude by 1 degree longitude) that were compared. Numbers in parentheses repre¬ 
sent the number of square degree areas (1 degree latitude, 1 degree longitude) with higher percent¬ 
ages of occurrence of Sargassum species during the coupling of AMO and NAO phases. 
U.S. Gulf 
of Mexico 
Water depth 
n 
Cold AMO, 
positive NAO 
phases 
Warm AMO, 
negative NAO 
phases 
Whole 
Continental shelf 
45 
1.36 ±0.44% (5) 
4.41 ±1.03% (34) 
P ,=0 
Deep basin 
26 
4.58 ±1.64% (4) 
7.42 ±1.43% (21) 
P;=0.0005 
Western 
Continental shelf 
22 
1.81 ±0.67% (3) 
5.17 ±1.62% (17) 
P;=0.0002 
Deep basin 
11 
7.28 ±2.99% (2) 
10.2 ±1.76% (9) 
P,=0.0375 
Eastern 
Continental shelf 
23 
0.93 ±0.53% (2) 
3.67 ±1.24% (17) 
P;=0.0002 
Deep basin 
15 
2.59 ±1.04% (2) 
5.40 ±1.43% (12) 
P,=0.0021 
Whole 
Continental shelf 
45 
1.36 ±0.44% 
4.41 ±1.03% 
Deep basin 
26 
4.58 ±1.64% 
7.42 ±1.43% 
P 2 <0.0001 
P 2 =0.0005 
Western 
Continental shelf 
22 
1.81 ±0.67% 
5.17 ±1.62% 
Deep basin 
11 
7.28 ±2.99% 
10.2 ±1.76% 
P 2 = 0.0002 
P,=0.0006 
Eastern 
Continental shelf 
23 
0.93 ±0.53% 
3.67 ±1.24% 
Deep basin 
15 
2.59 ±1.04% 
5.40 ±1.43% 
P 2 =0.0099 
P 2 =0.0183 
Pj-values given by the Wilcoxon signed rank test for the analysis between AMO and NAO phases. 
P 2 -values given by the Mann-Whitney U test for the analysis within AMO and NAO phases. 
est percentages of positive samples (Sargassum spe¬ 
cies present) occurred under the coupling of AMOw 
and NAOn phases regardless of region and season (Fig. 
1, Table 1). Regionally, higher percentages of positive 
samples occurred in the western GOM, regardless of 
season and climate regime (Table 1). Comparing the 
presence of Sargassum species over the continental 
shelf and deep basin during the summer, we found that 
occurrences were higher under the coupling of AMOw 
and NAOn phases regardless of region and water depth 
(Table 2). Occurrences were also higher over the deep 
basin regardless of region and climate phase (Table 2). 
Occurrence of species of Sargassum by ENSO event, 
region, continental shelf or deep basin waters during 
the summer is shown in Table 3. Presence of Sargas¬ 
sum species by region and over the deep basin was not 
significantly different among ENSO events. Presence of 
Sargassum species was higher in the continental shelf 
after ENSOc than after ENSOn events. Presence of 
species of Sargassum was higher in the western GOM 
after ENSOc and ENSOw events and in the deep basin 
regardless of an ENSO event. Occurrence of Sargas¬ 
sum species by ENSO events and regions during the 
fall is shown in Table 4. Higher values for presence 
of Sargassum species were noted in the western GOM 
regardless of an ENSO event. Highest, intermediate, 
and lowest values for the presence of Sargassum spe¬ 
cies were observed after ENSOc, ENSOn, and ENSOw 
years, respectively, regardless of region. 
Variability of weather-related hydrographic characteristics 
in the NERR and GOM in response to the coupling of 
AMO and NAO phases and ENSO events 
Monthly and seasonal weather-related hydrographic 
characteristics in the NERR and GOM showed math¬ 
ematically significant differences between the 2 AMO/ 
NAO phases (Table 5). During the coupled AMOw/ 
NAOn phase, higher values were found for the AMM 
index, the number of hurricanes, and the above av¬ 
erage annual discharge of the Amazon River in the 
NERR and the number of LC spin-off eddies, num- 
