100 
Fishery Bulletin 116(1) 
Table 3 
Mean summer (May-July) occurrence, with 95% confidence intervals, of pelagic species of Sargassum 
across the U.S. Gulf of Mexico and in the western and eastern regions, continental shelf, and deep basin 
after El Nino-Southern Oscillation (ENSO) events from 1982 through 2012. Occurrence represents the 
percentages of ichthyoplankton samples associated with pelagic Sargassum at the time of their collec¬ 
tion. Numbers in parentheses represent the total number of square degree areas (1 degree latitude by 
1 degree longitude) that were compared. Numbers in brackets represent the number of square degree 
areas with higher percentages of Sargassum species occurrence after ENSO events. NS=nonsignificant. 
U.S. Gulf of Mexico 
Cold ENSO 
Neutral ENSO 
Warm ENSO 
Whole 
_ 
_ 
_ 
P,=NS 
Western 
— 
— 
— 
P 7 = NS 
Eastern 
— 
— 
— 
P ; =NS 
Continental shelf 
3.43 ±0.91% (48) 
2.02 ±0.77% (48) 
2.52 ±0.66% (48) 
P;=0.0424 
Deep basin 
— 
— 
— 
P;=NS 
Continental shelf 
3.31 ±0.92% (48) [24] 
2.02 ±0.77% (48) [11] 
— 
P.,=0.0022 
P 2 =NS 
p 2 =ns 
Western 
4.64±1.10% (31) 
_ 
5.28±1.53% (32) 
Eastern 
3.62±1.29% (40) 
P 3 =0.0455 
p 3 =ns 
2.51±0.74% (40) 
P 3 =0.0020 
Continental shelf 
3.43±0.91% (48) 
2.02±0.77% (48) 
2.52±0.66% (48) 
Deep basin 
5.38±1.83% (23) 
P 3 =0.0188 
7.79±2.38% (24) 
P 3 <0.00001 
6.19±1.85% (24) 
P 3 =0.0002 
P ; -values given by the Kruskal-Wallis H test for the analysis among ENSO events. 
P 2 -values given by the Wilcoxon signed rank test for the analysis between ENSO events. 
P 3 -values given by the Mann-Whitney U test for the analysis within ENSO events. 
ber of hurricanes and the south and southeast wind 
momentums in the GOM. A seasonal weather-related 
hydrographic characteristic in the GOM was also sig¬ 
nificantly different under ENSO events. Higher val¬ 
ues of south wind momentum were detected at the 
western region in spring during ENSOc events (22.09 
±14.31 Ns/m 2 ) than during ENSOw events (6.02 
±2.93 Ns/m 2 ; P=0.007). Higher values of north and 
northwest wind momentum were found at the cen¬ 
tral region in spring during ENSOw events (N: 15.88 
±4.41 Ns/m 2 ; NW: 11.15 ±4.72 Ns/m 2 ) than during 
ENSOn events (N: 7.97 ±3.29 Ns/m 2 ; NW: 2.49 ±1.29 
Ns/m 2 ; P<0.006). 
Discussion 
Sargassum macroalgae in the western Atlantic Ocean 
are home to a diverse and unique community of small 
invertebrates and fish species. Despite the designation 
of Sargassurn species as essential fish habitat, long¬ 
term data on the distribution and abundance of species 
of Sargassum in the GOM are lacking. The time frame 
of the SEAMAP ichthyoplankton surveys provided a 
unique opportunity to examine occurrence of Sargas¬ 
sum species under differing decadal and interannual 
regimes of global climate. 
The GOM is part of a broader western Atlantic 
Ocean region of Sargassum occurrence. Historically, 
the recognized route of floating Sargassum macroalgae 
was through the Caribbean Sea, into the GOM, up the 
eastern seaboard of the United States within the Gulf 
Stream, and into the Sargasso Sea (Calder, 1995). Anew 
source area for Sargassum species in the tropical North 
Atlantic Ocean (NERR) was recently discovered (Franks 
et ah, 2011; Gower et ah, 2013; Johnson et ah, 2013) 
and provides another route of entry for the macroalgae 
to the greater Caribbean region and GOM. This newly 
defined route (NERR) has been cited as the source of the 
Sargassum species currently inundating the Caribbean 
region, and weather-related hydrographic characteris¬ 
tics (nutrient input, position and strength of the ITCZ) 
have been identified as contributors to the massive accu¬ 
mulation of the macroalgae (Franks et ah, 2011; Franks 
et ah, 2016). Weather-related hydrographic character¬ 
istics associated with the NERR (AMM, ITCZ, Amazon 
River discharge), as well as factors unique to the GOM 
(LC spin-off eddies) may help to explain differences in 
abundance of Sargassum species across the USGOM in 
response to shifts in climate regimes. 
