Sanchez-Rubio et al.: Occurrence of pelagic Sargassum in waters of the U.S. Gulf of Mexico 
95 
effort to collect, manage, and disseminate fishery-in- 
dependent data and information in the southeastern 
United States. The SEAMAP ichthyoplankton data¬ 
base (Hanisko 1 ) contains data on observed occurrence 
of pelagic Sargassum species in samples from surveys 
conducted across the USGOM. Data used for our study 
were prior to and lead up to the 2011 bloom in the 
tropical North Atlantic Ocean and are intended to pro¬ 
vide linkage to define the relationship between yearly 
and seasonal Sargassum occurrence in the USGOM 
and weather-related hydrographic regimes imposed by 
AMO, NAO, and ENSO events. Because the SEAMAP 
conducts surveys each year, the relationship of recent 
Caribbean and South American inundation events with 
Sargassum occurrence in the USGOM can be examined 
in the future. Reference to Sargassum occurrence in 
the following sections is specific to the pelagic species 
S. fluitans and S. natans. 
Material and methods 
Decadal AMO and NAO phases and interannual ENSO 
events 
Characterization of AMO and NAO phases and the 
individual ENSO events were adopted from Sanchez- 
Rubio and Perry (2015). Years not included in the lat¬ 
ter study (2011-2013) were placed under the coupled 
AMOw/NAOn (slash denotes coupling of those phases) 
phase and the 2011 year was identified as ENSOc. 
The coupling of AMOc and NAOp phases was in place 
from 1971 through 1994 (first regime, wet); the cou¬ 
pling of AMOw and NAOn phases was in place from 
1995 through 2013 (second regime, dry). Although the 
change from one phase to another is transitional, pub¬ 
lished studies cite the mid-1990s as the time when the 
shift occurred (Karnauskas et ah, 2015). The years 
from 1977 to 2010 were identified as ENSOw (1977, 
1982, 1986, 1987, 1991-1994, 1997, 2002, 2004, 2006, 
and 2009), ENSOn (1978-1981, 1985, 1989, 1990, 1995, 
1996, 2001, and 2003), and ENSOc (1983, 1984, 1988, 
1998-2000, 2005, 2007, 2008, 2010, and 2011) years. 
Biological data 
Biological data were taken from a series of ichthyo¬ 
plankton surveys conducted under the state and federal 
SEAMAP program administered by the NMFS. Data 
used to determine the occurrence of species of Sargas¬ 
sum were, in part, observational and therefore depen¬ 
dent upon the field biologists to record the presence of 
Sargassum species in the sample or sample area. Indi¬ 
viduals responsible for field collections were long-term 
employees of the NMFS thus there was continuity of 
1 Hanisko, D. S. 2015. Unpubl. data. [Historical data set 
of ichthyoplankton collected in 1982-2012 during Southeast 
Area Monitoring and Assessment Program surveys.] Miss. 
Lab., Southeast Fish. Sci. Cent., Natl. Mar. Fish. Serv., 
NOAA, 3209 Frederic St., Pascagoula, MS 39568-1207. 
personnel over the study period (personal observation 
and NMFS Cruise Reports, Harriet Perry). Although 
Sargassum species were not the primary focus of the 
surveys, their presence was recorded because they 
form important nursery habitat for commercially and 
recreationally sought fishes. Knowledge of the presence 
of Sargassum macroalgae aids in taxonomic resolution 
of species and provides information on the distribution 
of the Sargassum habitat. Acknowledging problems as¬ 
sociated with the use of observational data, the surveys 
still offer a unique opportunity to examine the rela¬ 
tionship between climate variables and algal presence 
because this data set provides the only long-term, sys¬ 
tematic information on the occurrence of these Sargas¬ 
sum species in the GOM. 
The SEAMAP ichthyoplankton database was ob¬ 
tained from Hanisko. 1 Data from samples in this sur¬ 
vey program were available from 1982 to 2012. The 
SEAMAP sampling area encompasses the USGOM from 
the 10-m isobath to the U.S. Exclusive Economic Zone. 
The sampling gear and methods used during SEAMAP 
surveys have been described by Kramer et al. (1972), 
Smith and Richardson (1977), and Posgay and Marak 
(1980). Most SEAMAP survey stations were occupied at 
approximately 56 km (or 0.5°) intervals in a fixed, sys¬ 
tematic grid of transects across the USGOM. Samples 
were taken upon arrival at each station regardless of 
time of day or night. Plankton surveys have been con¬ 
sistently conducted over 2 survey time frames (spring- 
early summer and late summer-early fall) since 1982 
(Lyczkowski-Shultz and Hanisko, 2007) and approxi¬ 
mately 200 stations have been targeted for sampling. 
In addition, numerous surveys have been periodically 
conducted over shorter time frames and with specific 
targeted species groups. For this study, the complete 
SEAMAP ichthyoplankton database (Hanisko 1 ) was 
used to increase temporal and spatial resolution of 
the data. Data on the occurrence of Sargassum spe¬ 
cies were obtained from direct observations recorded in 
ichthyoplankton data logs during SEAMAP cruises. In 
addition, the occurrence of species of Sargassum was 
indirectly inferred from the presence of the Sargassum- 
fish (Histrio histrio), a species endemic to Sargassum 
(Coston-Clements et al., 1991). 
Ichthyoplankton samples associated with Sargassum 
macroalgae were extracted from the main SEAMAP da¬ 
tabase to form a more manageable data set. The ex¬ 
tracted data set contained 1077 samples of which 1051 
were collected in neuston net tows and 26 in bongo net 
tows. All months of the year and most of the years, 
with the exception of 1982, 1987, and 1988, were rep¬ 
resented in the data set of ichthyoplankton samples 
associated with species of Sargassum. Of the 1077 
samples associated with Sargassum macroalgae, 284 
were collected under the coupling of AMOc and NAOp 
phases and 793 were collected during the coupling of 
AMOw and NAOn phases. Sargassum species occurred 
in samples from January to November during the cou¬ 
pling of AMOc and NAOp phases and from February 
to December during the coupling of AMOw and NAOn 
