348 
Abstract — The community structure 
of fishes associated with pelagic Sar- 
gassum spp. and open water lacking 
Sargassum was examined during 
summer and fall cruises, 1999-2003, 
in the Gulf Stream off North Caro- 
lina. Significantly more individual 
fishes ( n= 18,799), representing at 
least 80 species, were collected from 
samples containing Sargassum habi- 
tat, compared to 60 species (n = 2706 
individuals) collected from open- 
water habitat. The majority (96%) 
of fishes collected in both habitats 
were juveniles, and planehead filefish 
( Stephanolepis hispidus ) dominated 
both habitats. Regardless of sam- 
pling time (day or night), Sargassum 
habitat yielded significantly higher 
numbers of individuals and species 
compared with open-water collections. 
Overall, fishes collected by neuston 
net tows from Sargassum habitat were 
significantly larger in length than 
fishes collected from open-water habi- 
tat with neuston nets. A significant 
positive, linear relationship existed 
between numbers of fishes and the 
quantity of Sargassum collected by 
neuston net. Underwater video record- 
ings indicated a layered structure of 
fishes among and below the algae and 
that smaller fishes were more closely 
associated with the algae than larger 
fishes. Observations of schooling 
behaviors of filefishes (Monacanthi- 
dae), dolphinfish ( Coryphaena hip- 
purus), and jacks (Carangidae), and 
fish-jellyfish associations were also 
recorded with an underwater video 
camera. Our data indicate that Sar- 
gassum provides a substantial nurs- 
ery habitat for many juvenile fishes 
off the U.S. southeast coast. 
Manuscript submitted 12 February 2008. 
Manuscript accepted 6 June 2008. 
Fish. Bull. 106:348-363 (2008). 
The views and opinions expressed or 
implied in this article are those of the 
author and do not necessarily reflect 
the position of the National Marine 
Fisheries Service, NOAA. 
Fishes associated with pelagic Sargassum 
and open water lacking Sargassum 
in the Gulf Stream off North Carolina 
Tara L. Casazza (contact author) 
Steve W. Ross 
Email address for T.L. Casazza: tarac73@juno.com 
Center for Marine Science 
University of North Carolina Wilmington 
5600 Marvin Moss Lane 
Wilmington, North Carolina 28409 
In the western North Atlantic Ocean, 
pelagic brown algae of the genus Sar- 
gassum form a dynamic, floating habi- 
tat that supports a diverse assemblage 
of fishes, invertebrates, sea turtles, 
pelagic birds, and marine mam- 
mals. The pelagic species S. natans 
and S. fluitans provide resources in 
an otherwise nutrient-poor environ- 
ment and serve as a nursery area 
for many juvenile fishes (Wells and 
Rooker, 2004), some of which are com- 
mercially or recreationally important, 
or both (e.g., Coryphaena hippurus 
[dolphinfish], Caranx spp. [jacks], 
Seriola spp. [amberjacks]). Sargas- 
sum habitat appears to be particularly 
important for early survival of some 
fishes because the majority of fishes 
collected from Sargassum habitat in 
the Gulf of Mexico (Bortone et ah, 
1977; Wells and Rooker, 2004) and 
off the southeastern United States 
(Dooley, 1972; Moser et ah, 1998) are 
juveniles. 
The spatial distribution and quan- 
tity of Sargassum are highly variable. 
Sargassum distribution along the U.S. 
east coast depends on the Florida 
Current and the Gulf Stream, which 
entrain pelagic Sargassum from the 
Sargasso Sea and move it northward. 
Aggregations of Sargassum range 
from small, widely dispersed clumps 
to rafts and large weedlines that con- 
tinue for many kilometers, and the 
great variability in the structure of 
this habitat is due to variations in 
Gulf Stream flow, storms, tidal cur- 
rents, and wind-generated waves and 
currents. Although estimates of Sar- 
gassum biomass in the western North 
Atlantic have varied (Howard and 
Menzies, 1969; Butler and Stoner, 
1984), the majority of pelagic Sar- 
gassum has persisted and reproduced 
vegetatively in the western North At- 
lantic Ocean for at least decades and 
probably for hundreds to thousands of 
years (Parr, 1939). 
Sargassum habitat is extremely 
difficult to sample consistently and 
quantitatively, and no single meth- 
od of sampling provides a complete 
view of the Sargassum community. 
Even though Moser et al. (1998) rec- 
ommended using multiple sampling 
methods, especially visual methods, to 
survey this ecosystem, most Sargas- 
sum community studies from the Gulf 
of Mexico (Bortone et al., 1977; Wells 
and Rooker, 2004) and the western 
North Atlantic (Dooley, 1972; Moser et 
al., 1998) have been based on limited 
sampling methods. Kingsford (1995) 
and Dempster and Kingsford (2004) 
suggested that a weakness in previ- 
ous studies was a lack of open-water, 
unvegetated control samples, and to 
date, in only one study (Moser et ah, 
1998) in the western North Atlantic 
have fishes associated with Sargas- 
sum habitat been compared to fishes 
in open-water habitat. Additionally, 
most samples of Sargassum were col- 
lected during daytime only (Dooley, 
1972; Moser et al., 1998; Wells and 
Rooker, 2004) or sampling times were 
not specified (Bortone et ah, 1977; 
Stoner and Greening, 1984). In some 
cases, explicit association of samples 
with Sargassum was unclear because 
samples were not collected within the 
algae (e.g., Settle, 1993). 
