Shifts in an epibenthic trophic web across a marine frontal area in the Southwestern Atlantic (Argentina) A. Cecilia Mauna a, ⁎, Florencia Botto b, d , Barbara Franco c , J. Matías Schwartz a , E. Marcelo Acha a, b, d , Mario L. Lasta a , Oscar O. Iribarne b, d a Instituto Nacional de Investigación y Desarrollo Pesquero (INIDEP), Paseo V. Ocampo No. 1, Mar del Plata, B7602HSA, Argentina b Consejo Nacional de Investigaciones Cientíﬁcas y Técnicas (CONICET), Rivadavia 1906, Buenos Aires, 1033, Argentina c Departamento Oceanografía, Servicio de Hidrografía Naval (SHN), Av. Montes de Oca 2124, Buenos Aires, D1270ABV, Argentina d Instituto de Investigaciones Marinas y Costeras (Universidad Nacional de Mar del Plata y Consejo Nacional de Investigaciones Cientíﬁcas y Técnicas), CC 573 Correo Central, B7600WAG Mar del Plata, Argentina abstract article info Article history: Received 6 April 2011 Received in revised form 26 July 2011 Accepted 27 August 2011 Available online 9 September 2011 Keywords: Epibenthos Food web Macroinvertebrate diet stable isotope Marine front SW Atlantic Marine benthic trophic relationships and food web structures may be inﬂuenced by benthic–pelagic coupling processes, which could also be intensiﬁed by the physical dynamics of marine fronts. In this work, we employed stable isotope (δ 13 C and δ 15 N) analysis to investigate the inﬂuence of the Southwest (SW) Atlantic shelf-break front (SBF; 38–39°S, 55–56°W; Argentina) on an epibenthic trophic web. Epibenthic organisms were sampled, at depths of ~ 100 m, with a non-selective dredge from a sandy bottom community located in frontal (F) and marginal (M) areas. The SBF position and the chlorophyll-a (chl-a) concentrations were in- ferred using satellite data of the sea surface temperature (SST) and satellite chl-a concentration, respectively. The most noticeable shifts in stable isotopes between the sampled areas were those of the Patagonian scallop, Zygochlamys patagonica (δ 13 C), and those of the sea urchin, Sterechinus agassizi (δ 15 N). Diet analyses inferred from stable isotopes and mixing models demonstrated that the dominant component of this community, Z. patagonica, had variable contributions to higher trophic levels between areas. More importantly, the epibenthic assemblage in F areas showed δ 13 C-enriched and δ 15 N-depleted isotopic signatures with respect to the M areas. Collectively, this evidence suggests that frontal dynamics promotes the accumulation of δ 13 C-enriched phytoplankton in the seabed in F areas, while in M areas the more degraded organic matter becomes more important in the trophic web, decreasing the δ 15 N isotopic signature of the assemblage. Therefore, the trophic web was sustained by fresher food in F areas than in M areas, demonstrating the role of frontal dynamics in the shaping of these communities. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Trophic relationships between organisms, or even the complete food web structure in marine benthic communities, can be inﬂuenced by benthic–pelagic coupling (Dauwe et al., 1998; Menge et al., 1997; Norkko et al., 2007). This coupling is absolutely necessary for communi- ties located at considerable depths because it allows the phytoplankton that are produced in euphotic zones to reach such depths (Graf, 1992). Once near or on the seaﬂoor, the sedimented phytoplankton is consumed by many trophic guilds. Phytoplankton is often initially consumed by suspension feeders or by surface deposit feeders before becoming incorporated into the sediment (Josefson and Conley, 1997). Then, the food remains are ingested by sediment-inhabiting bacteria (Lochte and Turley, 1988) and/or by detritivores of a variety of sizes (Graf, 1992). This general pattern may be inﬂuenced by ocean- ographic conditions that are able to alter phytoplankton sedimentation rates (Allan et al., 2010; Dauwe et al., 1998). As a result, environments with intermittent, strong currents and abundant, suspended sediment allow for high densities of suspension feeders (Dauwe et al., 1998); in contrast, in environments where ﬂows can cause the rapid burial of organic-rich sediments, the concentration of subsurface deposit-feeders tends to increase (Shields and Hughes, 2009). Thus, all evidence suggests that food supply through pelagic–benthic connections can affect the properties of benthic communities' structures and ecosystems (Rooney et al., 2006). Marine fronts can greatly increase the benthic–pelagic coupling, playing an important role in structuring benthic communities (Dewicke et al., 2002; Josefson and Conley, 1997). These fronts are usually characterized by high biological production (e.g., Carroll et al., 2008; Mann and Lazier, 1996), they offer feeding and/or reproduc- tive habitats for many taxa (e.g., Bakum, 2006; Dewicke et al., 2002), they act as larval retention areas of benthic species (e.g., Shanks et al., Journal of Sea Research 66 (2011) 248–255 ⁎ Corresponding author. Tel.: + 54 223 4862586; fax: + 54 223 4861850. E-mail address: cmauna-fuentes@inidep.edu.ar (A.C. Mauna). 1385-1101/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.seares.2011.08.005 Contents lists available at SciVerse ScienceDirect Journal of Sea Research journal homepage: www.elsevier.com/locate/seares