Megavertebrate Communities from Two Contrasting Ecosystems in the Western Tropical Atlantic

MARSYS-02299; No of Pages 15 Journal of Marine Systems xxx (2012) xxx–xxx Contents lists available at SciVerse ScienceDirect Journal of Marine Systems journal homepage: www.elsevier.com/locate/jmarsys Megavertebrate communities from two contrasting ecosystems in the western tropical Atlantic Laura Mannocci a,⁎, Pascal Monestiez b, Jaime Bolaños-Jiménez c, Ghislain Dorémus d, Stéphane Jeremie e, Sophie Laran d, Renato Rinaldi f, Olivier Van Canneyt d, Vincent Ridoux a,d a Laboratoire Littoral Environnement et Sociétés, UMR 7266 Université de La Rochelle-CNRS, Institut du Littoral et de l'Environnement, 2 rue Olympe de Gouges, 17000 La Rochelle, France b INRA, UR0546, Unité Biostatistique et Processus Spatiaux, Domaine Saint Paul, Site Agroparc, 84914 Avignon, France c Sociedad Ecológica Venezolana Vida Marina, AP 162, Cagua, Estado Aragua 2122, Venezuela d Observatoire PELAGIS, Systèmes d'Observation pour la Conservation des Mammifères et des Oiseaux Marins, UMS 3462 Université de La Rochelle-CNRS, Pôle analytique, 5 allées de l'Océan, 17000 La Rochelle, France e Société pour l'Etude, la Protection et l'Aménagement de la Nature à la Martinique, MBE 208 Mango Vulcin, 97288 Lamentin Cedex 02, France f Association Evasion Tropicale, rue des palétuviers, 97125 Pigeon Bouillante, France article info abstract Article history: Productivity was shown to structure megavertebrate communities, particularly in tropical oceans where they may Received 25 April 2012 be under selective pressure to maintain their foraging success in these low productivity environments. However, Received in revised form 5 November 2012 overall oligotrophic tropical oceans may encompass contrasting ecosystems. In the western tropical Atlantic, the Accepted 5 November 2012 Antilles and Guiana belong to two different biogeographic provinces and surface chlorophyll concentration is on Available online xxxx average 10 times higher in Guiana. The aim of this study was to document megavertebrate communities in terms of encounter rates, species composition, abundance and spatial distribution and to compare them between Keywords: Megavertebrates these two contrasting regions. As part of an aerial census of cetaceans and other megavertebrates, line transect Cetaceans surveys were conducted across the French Antilles and Guiana. Both distance sampling and geostatistics were Seabirds used to estimate abundance and geostatistics also provided maps of local density. Cetacean encounter rate was Aerial survey 3 times higher in Guiana (1.8 sightings/100 km) compared to the Antilles (0.6 sightings/100 km). Moreover, Antilles small delphinids strongly dominated in Guiana (representing 83% of the odontocete sightings) with a high abun- Guiana dance of bottlenose dolphins (Tursiops truncatus) (34,965 individuals, CV=0.28). Seabird encounter rate was sim- Productivity ilar in both regions (4.7 sightings/100 km in the Antilles and 3.6 sightings/100 km in Guiana). Charadriiformes, Encounter rate mainly represented by terns, were abundant in both regions whereas Pelecaniformes were only abundant in the Community composition Abundance Antilles and represented by frigatebirds, tropicbirds and boobies. Additionally, cetaceans and seabirds were mainly Density distributed close to the islands in the Antilles and were more widely distributed in Guiana. This study provided new information about megavertebrates which are poorly documented in these waters and highlighted differ- ences in communities between these contrasting ecosystems. In particular, odontocete communities appeared to respond to productivity and may be structured by a differential distribution of resources through the water column. © 2012 Elsevier B.V. All rights reserved. 1. Introduction be surveyed across large oceanic regions; it is therefore expected that their species assemblages reveal some of the major properties of the Top marine predators, or upper trophic level predators, refer to large underlying ecosystems. This characteristic is referred to as the indicator marine vertebrates which have no predators of their own (Pimm et al., value (Boyd et al., 2006; Zacharias and Roff, 2001). 1991) and occupy a food's web highest trophic level (Estes et al., Indeed, megavertebrates respond to the variability of the ecosys- 2001). Along with some mid trophic level predators, they form the tems in which they live. Notably, changes in prey abundance are megavertebrates, which include a variety of taxa: marine mammals, sea- thought to affect cetaceans and seabirds in many ecosystems birds, sea turtles, elasmobranches, predatory fishes… Megavertebrates (Furness and Tasker, 2000; MacLeod et al., 2007; Reid et al., 2005; (especially air breathing species), form one of the few components of Soto et al., 2004). However, as extensive sampling of prey is difficult, pelagic biodiversity that can be seen from the surface of the ocean and surface productivity is often used as a proxy for prey abundance over large spatial domains (e.g. Ballance et al., 1997). Surface productivity ⁎ Corresponding author. Tel.: +33 5 46 50 76 48; fax: +33 5 46 50 76 63. has been shown to structure cetacean and seabird communities over E-mail address: [email protected] (L. Mannocci). large spatial scales in the three oceans (Ballance et al., 1997; 0924-7963/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jmarsys.2012.11.002 Please cite this article as: Mannocci, L., et al., Megavertebrate communities from two contrasting ecosystems in the western tropical Atlantic, J. Mar. Syst. (2012), http://dx.doi.org/10.1016/j.jmarsys.2012.11.002 2 L. Mannocci et al. / Journal of Marine Systems xxx (2012) xxx–xxx Hyrenbach et al., 2007; Schick et al., 2011; Smith and Hyrenbach, 2. Material and methods 2003). In the eastern tropical Pacific, seabird communities were structured along a surface productivity gradient (Ballance et al., 2.1. Study regions 1997). In the Indian Ocean, Hyrenbach et al. (2007) observed changes in seabird density and community composition along a latitudinal In Guiana, the French EEZ (4–9°N, 49–54°W), spanning 132,000 km2, gradient; seabird densities being higher in the cooler and productive extends 200NM into the Atlantic Ocean, including a broad continental sub-Antarctic waters compared to the less productive subtropical wa- shelf, a slope, wider on its western part and an abyssal plain where ters. Schick et al. (2011) studied cetacean community structure over depths approach 4500 m (Fig. 1). Several rivers open into these waters three biogeographic provinces in the Atlantic Ocean and described (Approuague, Oyapock,andMaroni)aswellastheAmazonplume.Asa two different groups of cetaceans along a surface chlorophyll consequence, extensive mudflats are present along the coast and coastal gradient. waters are highly turbid (Froidefond et al., 1988). Local oceanography Tropical oceans, which represent 50% of total ocean area, are charac- is strongly influenced by the variability of river discharge, maximum terized by low productivity and hence scarce food resources (Longhurst in May–June and minimum in November. The Amazon plume is and Pauly, 1987). Therefore, tropical species may be under selective retroflected during boreal summer (July to December) when the North pressure to maintain their foraging success in the face of these dimin- Brazilian Current is the strongest (Longhurst, 2007, Fig. 1). Moreover, ished feeding opportunities (Ballance and Pitman, 1999). Unfortunately, wind-driven coastal upwelling occurs, as indicated by the presence of little is known about megavertebrates inhabiting tropical open oceans. cool water in the upper 10 m (Gibbs, 1980). Productivity is highly While some regions have been intensively surveyed in space and time seasonal and maximal during summer. However, chlorophyll biomass (e.g. the eastern tropical Pacific Ballance et al., 1997, 2006; Redfern inferred from remote sensing may be unreliable since the color of the et al., 2008), nearly nothing is known in certain regions (in general water in the river plumes is dominated by dissolved organic matters studies have focused on inshore areas whereas pelagic waters were rather than chlorophyll light absorption (Hu et al., 2004). poorly surveyed). The French EEZ in the Antilles (14–19°N, 57–64°W), spanning The REMMOA program (REcensements des Mammifères marins 143,000 km2, extends from Guadeloupe and Martinique Islands, et autre Mégafaune pélagique par Observation Aérienne, Census of 200NM into the Atlantic Ocean and 80NM into the Caribbean Sea marine mammals and other pelagic megafauna by aerial survey) was and northward around St Barthélemy and St Martin islands (Fig. 1). implemented to establish a baseline knowledge on megavertebrates These volcanic islands are characterized by narrow submarine shelves in French tropical waters. The first dedicated surveys were conducted and a steep dropping of the sea floor, especially in the Caribbean Sea. in 2008, across the Exclusive Economic Zones (EEZs) of the Antilles Despite high biological productivity along the coasts, Caribbean and Guiana, in the western tropical Atlantic. Indeed, apart from the pelagic waters are relatively oligotrophic and characterized by a Gulf of Mexico, where large scale surveys resulted in a basic under- permanent stratification (Longhurst, 2007). The regime of winds, standing of distribution, abundance and habitats of cetaceans and influenced by the displacement of the Intertropical Convergence seabirds (e.g. Baumgartner et al., 2001; Davis et al., 2002; Fulling

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