Benthic community composition and faunal stable isotopic signatures differ across small spatial scales in a temperate estuary Ylva S. Olsen a, * , Sophia E. Fox a,1 , Laurie Hofmann b , Ivan Valiela a a The Ecosystems Center, Marine Biological Laboratory, 7 MBL St, Woods Hole, MA 02543, USA b Bremen Marine Ecology Center for Research and Education, University of Bremen, Leobener Str. NW2, 28359 Bremen, Germany article info Article history: Received 5 October 2012 Received in revised form 5 February 2013 Accepted 8 February 2013 Keywords: Benthic ecology Estuaries Habitat Isotopes Zostera marina Vegetation Carbon assimilation Consumers abstract Anthropogenically induced changes to estuaries, including shifts from seagrass to macroalgae-dominated habitats, have led to concerns about the ability of estuaries to support fish and invertebrates. To assess differences in habitat quality of seagrass and macroalgae, we examined faunal community structure and consumer carbon assimilation in adjacent areas of seagrass, macroalgae, and bare sediments in Sage Lot Pond, Waquoit Bay, MA. Vegetation was an important factor controlling abundances, and both seagrass and macroalgae provided suitable habitat for a range of benthic fauna. Differences in consumption and assimilation of carbon of seagrass and macroalgal origin were demonstrated by shifts in d 13 C values of consumers between the seagrass meadow and adjacent macroalgal mats. Overall, consumers generally reflected incorporation of carbon from the dominant producers in the habitat where they were collected although macroalgae was an important carbon source for organisms in this study. These results revealed differences in carbon flow from producers to consumers across very small spatial scales (<10 m) within an estuary. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction The estuarine benthos is heterogeneous and may be made up of a mosaic of different habitats including bare sediment, macroalgal mats and seagrass meadows. Human activities on land have dras- tically altered this subtidal landscape. Eutrophication has fuelled proliferation of macroalgae, which limits light availability for sea- grasses, and can ultimately lead to shifts from seagrass meadows to macroalgae-dominated habitats (McGlathery, 2001; Hauxwell et al., 2003). Changes to subtidal habitats have led to concerns about the ability of estuaries to support fish and invertebrates that are both ecologically and economically important (Valiela et al., 1992; Hauxwell et al., 1998; Hughes et al., 2002). Macrophytes typically support higher densities of fish and invertebrates, and have enhanced diversity and higher rates of survival compared to adjacent unvegetated habitats (Orth et al., 1984; Sogard and Able, 1991; Orth, 1992; Lee et al., 2001). Submerged vegetation plays important roles in providing structured and complex habitat as refugia against predation (Heck and Thoman, 1981; Heck and Wilson, 1987) and food (Orth et al., 1984; Connolly, 1997; Mattila et al., 1999; Heck et al., 2003). Macroalgae are a nutritious food source for many invertebrates and fish, whereas seagrass tends to be less palatable and enter the food web mainly as detritus (Cebrián, 1999). Seagrasses, however, support a diverse epiphyte community that is heavily grazed by small invertebrates (Orth and Van Montfrans, 1984; Neckles et al., 1993). Benthic producers differ in their abilities to support faunal communities. For example, in a temperate estuary, epibenthic fish and some crustaceans were more abundant in eelgrass (Zostera marina) meadows compared to sites where the macroalga Ulva lactuca was the dominant vegeta- tion type, suggesting that macroalgal cover was not an equivalent substitute for eelgrass (Sogard and Able, 1991). Changes in benthic habitat structure and the availability of food and shelter can therefore alter the faunal community in both abundance and taxonomic composition. Changes in the relative abundances and composition of benthic producers and consumers have implications for trophic relation- ships and benthic food webs (Fox et al., 2009; Olsen et al., 2011). To examine trophic relationships among organisms and the origins of organic matter incorporated into food webs, we can use stable isotopes of carbon (d 13 C) and nitrogen (d 15 N) (Peterson and Fry, * Corresponding author. Present address: The Oceans Institute, The University of Western Australia, 35 Stirling Hwy, Crawley, WA 6009, Australia. Tel.: þ61 8 6488 5907. E-mail address: ylva.olsen@uwa.edu.au (Y.S. Olsen). 1 Present address: National Park Service, Cape Cod National Seashore, 99 Marconi Site Road, Wellfleet, MA 02667, USA. Contents lists available at SciVerse ScienceDirect Marine Environmental Research journal homepage: www.elsevier.com/locate/marenvrev 0141-1136/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.marenvres.2013.02.002 Marine Environmental Research 86 (2013) 12e20