Intraspecific diet shift in Talitrus saltator inhabiting exposed sandy beaches Celia Olabarria a , Mo ´ nica Incera b, * , Josefina Garrido a , Iva ´n F. Rodil a , Francesca Rossi c a Departamento de Ecologı ´a y Biologı ´a Animal, Universidad de Vigo, 36310 Vigo, Spain b Centro Tecnolo ´gico del Mar-Fundacio ´n CETMAR, 36208 Vigo, Spain c IMAR – CMA Marine and Environmental Research Centre University of Coimbra, Coimbra, Portugal article info Article history: Received 26 February 2009 Accepted 22 June 2009 Available online 27 June 2009 Keywords: stable isotopes stranded algae food sources diet shift sandy beaches Talitrus saltator Sargassum muticum Galician coast abstract Talitrid amphipods are the most abundant herbivores on exposed sandy beaches. Despite their important role as trophic intermediates between macrophytes and higher levels (i.e. insect and bird) of beach food webs, very little information is available on their feeding patterns. The main aim of this study was to investigate intraspecific differences in the feeding behaviour of Talitrus saltator . We tested the hypotheses that: (1) adult females and males showed different isotope signatures and therefore relied on different sources of food; and (2) patterns of variation of isotope signatures of juveniles differed from those of adult specimens, evidencing a diet shift during the development. We used stable isotope signatures and tested for differences upon the level on the shore, times of the year and beaches experiencing similar morpho-dynamic and environmental conditions. Finally, we investigated the trophic significance of macrophyte detritus in the diet of males, females and juveniles. Results showed that adult males had a more variable diet than females and juveniles (inferred from d 13 C and d 15 N values). Dual-isotope graphs suggested that Sargassum muticum and Cystoseira baccata wrack could be among the main food sources for both juvenile and adult stage. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction On exposed sandy beaches of temperate regions, the major sources of food are often marine macrophytes (macroalgae, sea- grasses) because little primary production occurs on the beach itself (e.g. Brown and McLachlan, 1990; Dugan et al., 2003). Hence, macrofaunal assemblages of exposed sandy beaches depend largely upon allochthonous inputs from the coastal ocean that arrive as stranded wrack (e.g. Kirkman and Kendrick, 1997; Colombini and Chelazzi, 2003; Lastra et al., 2008). This benefit may also extend beyond the beach itself. For example, wrack deposited along shorelines is consumed by detritivores and scavengers, which in turn are important food sources for vertebrate predators such as shorebirds, seabirds, lizards, rodents, marine mammals, and fishes (Polis et al., 1997). Despite the role of wrack as food subsidy for the macrofauna inhabiting sandy beaches, its trophic significance has proved difficult to evaluate in the field (e.g. Griffiths and Stenton- Dozey, 1981; Jedrzejczak, 2002). Talitrid amphipods are some of the most abundant sand inhabitants on exposed beaches (e.g. Dugan et al., 2003; Lastra et al., 2006) and important consumers of wrack (Dugan et al., 2003). Their rate of consumption may be affected by several processes, such as competition with other consumers, physico- chemical and morphological characteristics of the macrophyte species, and availability of wrack (Van Alstyne et al., 2001; Orr et al., 2005). For instance, abundance, and identity of the consumers and the spatial and temporal variability of wrack composition could influence the processing and availability of macrophyte wrack and as a consequence, abundance and feeding behaviour of amphipods (Dugan et al., 2003). Accumulating evidences suggest that benthic invertebrates might change their diet as they grow (Bergman and Greenberg, 1994; Polis et al., 1997; Hentschel, 1998; Rossi et al., 2004). Onto- genetic shifts in diets can have dramatic effects on the structure and composition of benthic assemblages (e.g. Cohen et al., 1993; Hentschel, 1998). For example, size-specific competition for food resources may limit population densities of deposit-feeding species (Hentschel and Jumars, 1994). Thus when an ontogenetic change in diet occurs, descriptions of food webs should distinguish among the size classes or life cycle stages on that species (Cohen et al., 1993). In addition, sex-related differences in diet have been reported as a fairly common phenomenon in marine organisms * Corresponding author. E-mail addresses: colabarria@uvigo.es (C. Olabarria), mincera@cetmar.org (M. Incera), f_rossi@zoo.uc.pt (F. Rossi). Contents lists available at ScienceDirect Estuarine, Coastal and Shelf Science journal homepage: www.elsevier.com/locate/ecss 0272-7714/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.ecss.2009.06.021 Estuarine, Coastal and Shelf Science 84 (2009) 282–288