Birds of Indian Subcontinent

Seabird Patchiness in Tropical Oceanic Waters: The Influence of Sargassum "Reefs"

Publication Type:Journal Article
Year of Publication:1986
Authors:J. Haney, C
Journal:The Auk
Date Published:1986
ISBN Number:00048038
Keywords:Alcidae, Atlantic Ocean, Chlidonias, Chlidonias niger, Chlidonias nigra, Fratercula, Fratercula arctica, Haliplana anaethetus, Laridae, Niger, North Atlantic Ocean, Onychoprion, Onychoprion anaethetus, Phaethon, Phaethon lepturus, Phaethontidae, Procellariidae, Puffinus, Puffinus lherminieri, Sterna, Sterna anaethetus, Sterna nigra, Sula, Sula dactylatra, Sulidae, United States
Abstract:The relationships of seabirds to the holopelagic macroalga Sargassum were studied during a 2-yr survey in the South Atlantic Bight off the southeastern United States. Seabirds were significantly more abundant in waters with large (>5 m2) patches of the alga, and mean avian density was 32-43 times greater in waters where Sargassum was present than in adjacent waters without the alga. Seabirds aggregate at Sargassum patches formed by Langmuir circulation, convergence fronts, Gulf Stream eddies, and Gulf Stream warm core rings. Twenty-three seabird species foraged at Sargassum. Significantly more than 50% of White-tailed Tropicbirds (Phaethon lepturus), Masked Boobies (Sula dactylatra), and Bridled Terns (Sterna anaethetus) were observed at algal patches. Species that use aerial-dipping and plunge-diving foraging behaviors displayed the greatest affinity for Sargassum. Large-bodied seabirds (large shearwaters, tropicbirds, and boobies) generally were found at large patches, while small-bodied species (phalaropes and Puffinus lherminieri) occurred at smaller patches. The seasonal abundance of the pelagic Bridled Tern corresponded to seasonal variation in Sargassum abundance. Most seabirds associated with Sargassum for foraging, but Bridled and Black terns (Chlidonias niger) also used large algal mats for roost sites. The highly localized biomass of the pelagic Sargassum community and its associated motile macrofauna (zooplankton and fish) may allow seabirds to forage efficiently for prey in the oligotrophic surface waters of tropical marine environments. The patchy occurrence of Sargassum "reefs" may explain part of the local and mesoscale variation in seabird distribution and abundance in portions of the western North Atlantic Ocean.
Short Title:The Auk
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