Moser and Lee • SARGASSUM REEFS AND SEABIRD FORAGING 
71 
I Numerical percentage (numbers of prey item 
^ divided by the total number of prey items X 100) ol 
V«a«unt-associated fishes in the digestive tracts of 
Chon's Shearwaters (A) (// = 48). Bridled Terns (Bl 
16). and Royal Terns (Cj (n = 8). 
' ■"ntnute daily from Outer Banks nesting colonies 
,IJ forage in Sargassum mats along ihe edge ol 
,hc outer continental shelf, a round trip of up to 
160 km or more (DSL. unpubl. data). Common 
lS,f w hirundo) and Black ( Chlidonias niger ) 
le nis, and Sabine's Gulls seasonally migrate north 
^ south, and likely use rows of Sargassum along 
the western edge of the Gulf Stream and drift lines 
within the Stream to both orient and feed. 
Reduction in the Sargassum community would 
have negative effects on a number of western 
North Atlantic seabirds, based on digestive tract 
analysis and at-sea observations, including five 
tropical species considered to be of conservation 
concern (Schreiber 2000). Observations of Ber¬ 
muda Petrels (Pterodronui t allow) and Roseate 
Terns ( Sterna dougallii) indicated these Endan¬ 
gered Species also use Sargassum to forage. 
Sargassum use by seabirds in the Pacific and 
Indian oceans is unknown, but it is likely that 
many of the same species and their ecological 
counterparts exploit Sargassum reefs in those 
oceans as well. Commercial harvest threatens to 
reduce the standing crop of Sargassum in the 
western North Atlantic (Settle 1997). and there are 
possible negative impacts to Sargassum from oil 
and gas exploration on the outer Continental 
Shelf off the coast of North Carolina (Lee 1999). 
Seabird surveys in the Gulf of Mexico shortly 
after the Deepwater Horizon oil spill (April 2010) 
indicated Sargassum habitat was damaged by this 
event (J. C. Haney and DSL. unpubl. data). Global 
climate change and attendant ocean acidification 
may also affect Sargassum (Porzio et al. 2011). 
Significant reduction in the amount or quality of 
Sargassum habitat could reduce seabird abun¬ 
dance, influence marine distribution, alter season¬ 
al movements, and/or jeopardize the birds 
physiological condition. 
ACKNOWLEDGMENTS 
Wc thank S. W. Ross Cor help with fish identification 
and Cor reviewing an early version ol this manuscript. H. J. 
Porter aided in gastropod identification. .1. M. Butzerin, 
T P. Good. J. C. Haney. W. A. Mackin. R. L. Pitman, and 
an anonymous reviewer provided helpful reviews of this 
manuscript. Funding Cor this study was provided in part by 
Ihe National Marine Fisheries Service, U.S. Fish and 
Wildlife Service. U.S. Army Corps of Engineers, and U.S. 
Department of the Navy. 
LITERATURE CITED 
Asiimole. N. P. 1971. Seabird ecology and the marine 
environment. Pages 223-286 in Avian Biology (D. S. 
Famer and J. R. King. Editors). Volume J. Academic 
Press. New York, USA. 
Casazza. T. L. and S. W. Ross. 2008. Fishes associated 
with pelagic Sargassum and open water Jacking 
Sargassum in the Gulf Stream off North Carolina. 
Fishery Bulletin 106:348-363. 
Dooley. J. K. 1972. Fishes associated with the pelagic 
Sargassum complex, with a discussion of the Sargus- 
