Casazza and Ross: Fishes associated with pelagic Sargassum and open water off North Carolina 
359 
Sargassum wet weight (kg) 
Figure 4 
Relationships between number of individuals and Sargassu/n wet weight (kg) for five abun- 
dant fish species collected with neuston nets in Sargassum habitat during summer and fall 
of 2000-2003 off North Carolina. Note differences in y-axis scale. 
(Stoner, 1983), the strong association of small fishes with 
Sargassum and their behaviors around the algae indi- 
cates that this habitat provides shelter from predation. 
Schooling of A. monoceros to mimic floating seaweed 
(Crawford and Powers, 1953) and the camouflage color- 
ation of juvenile monacanthids, balistids, and other taxa 
within Sargassum fronds help conceal them from preda- 
tors (Fig. 5, A and D). The increasingly close association 
of fishes to the floating algae with decreasing fish size 
further indicates a strong role of the habitat in mitigat- 
ing predation. Larger fishes, like adult dolphinfishes 
and jacks, aggregating below the weedlines, appeared to 
use Sargassum primarily during feeding (Dooley, 1972; 
Moser et al., 1998; this study). Sargassum habitat seems 
to provide an ecological advantage as illustrated by the 
trend of several species exhibiting larger sizes in Sargas- 
sum habitat compared to open-water habitat, but it is not 
clear if this advantage results from better food resources 
or lack of predation within the algal habitat. 
As a result of intensive sampling, the number of fish 
species known to associate with Sargassum habitat in 
U.S. waters was substantially increased. Eighty fish 
species were collected in association with Sargassum 
in this study, forty-one percent of which had not been 
previously reported in association with pelagic Sargas- 
sum. Mesopelagic fishes spend most of their lives in a 
habitat lacking structure and have not been reported 
to seek structured habitats. Thus, the seven species of 
