Community structure across a large-scale ocean productivity gradient: Marine bird assemblages of the Southern Indian Ocean

David K. Hyrenbach (1) , Richard R. Veit (2) , Henri Weimerskirch (3) , Nicolas Metzl (4) , George L. Hunt Jr. (5)

1 Duke University Marine Laboratory
2 CSI-CUNY
3 CEBC - Centre d'Études Biologiques de Chizé
4 LOCEAN - Laboratoire d'Océanographie et du Climat : Expérimentations et Approches Numériques
5 Department of Ecology and Evolutionary Biology

Our objective was to understand how marine birds respond to oceanographic variability across the Southern Indian Ocean using data collected during an 16-day cruise (4-21 January 2003). We quantified concurrent water mass distributions, ocean productivity patterns, and seabird distributions across a heterogeneous pelagic ecosystem from subtropical to sub-Antarctic waters. We surveyed 5155km and sighted 15,606 birds from 51 species, and used these data to investigate how seabirds respond to spatial variability in the structure and productivity of the ocean. We addressed two spatial scales: the structure of seabird communities across macro-mega scale (1000 s km) biogeographic domains, and their coarse-scale (10 s km) aggregation at hydrographic and bathymetric gradients. Both seabird density and species composition changed with latitudinal and onshore-offshore gradients in depth, water temperature, and chlorophyll-a concentration. The average seabird density increased across the subtropical convergence (STC) from 2.4 birdskm² in subtropical waters to 23.8 birdskm² in sub-Antarctic waters. The composition of the avifauna also differed across biogeographic domains. Prions (Pachyptila spp.) accounted for 57% of all sub-Antarctic birds, wedge-tailed shearwaters (Puffinus pacificus) accounted for 46% of all subtropical birds, and Indian Ocean yellow-nosed albatross (Thallasarche carteri) accounted for 32% of all birds in the STC. While surface feeders were the most abundant foraging guild across the study area, divers were disproportionately more numerous in the sub-Antarctic domain, and plungers were disproportionately more abundant in subtropical waters. Seabird densities were also higher within shallow shelf-slope regions, especially in sub-Antarctic waters, where large numbers of breeding seabirds concentrated. However, we did not find elevated seabird densities along the STC, suggesting that this broad frontal region is not a site of enhanced aggregation.

Mots clés: Crozet Basin; Species assemblages; Remote sensing; Seabirds; Ocean productivity; Oceanic fronts; Community structure; Indian Ocean

Domaines: Biodiversité et Ecologie; Environnement et Société; Milieux et Changements globaux

David K. Hyrenbach, Richard R. Veit, Henri Weimerskirch, Nicolas Metzl, George L. Hunt Jr.. Community structure across a large-scale ocean productivity gradient: Marine bird assemblages of the Southern Indian Ocean. Deep Sea Research Part I: Oceanographic Research Papers, 2007, 54 (7), pp.1129-1145. ⟨10.1016/j.dsr.2007.05.002⟩. ⟨hal-00266841⟩