Effects of particle surface properties on feeding selectivity in the eastern oyster Crassostrea virginica and the blue mussel Mytilus edulis Maria Rosa a, ⁎, J. Evan Ward a , Sandra E. Shumway a , Gary H. Wikfors b , Emmanuelle Pales-Espinosa c , Bassem Allam c a Department of Marine Sciences, University of Connecticut, 1080 Shennecossett Road, Groton, CT 06340, USA b NOAA, National Marine Fisheries Service, Northeast Fisheries Science Center, 212 Rogers Avenue, Milford, CT, USA c School of Marine and Atmospheric Sciences, Stony Brook University, Stony Brook, NY 11794, USA abstract article info Article history: Received 26 November 2012 Received in revised form 16 April 2013 Accepted 17 May 2013 Available online xxxx Keywords: Bivalve feeding Crassostrea virginica Mussel Mytilus edulis Oyster Particle selection The mechanisms by which bivalve molluscs differentiate among particles are not clearly understood. Recent evidence suggests that particle selection by bivalves can be mediated by interactions between carbohydrates attached to a particle's surface and lectins present in the mucus covering the feeding organs. The physico- chemical surface properties of particles have also been proposed as factors contributing to particle selection. In this study, we examined the effects of surface charge and wettability of 10-μm spheres on particle selection by two species of suspension-feeding bivalves: eastern oysters (Crassostrea virginica) and blue mussels (Mytilus edulis). Microspheres were delivered to bivalves in particle-selection assays, and the proportions of spheres rejected as pseudofeces and egested as feces were determined using flow cytometry. Results sug- gest that when given a choice, both mussels and oysters rejected some types of microspheres (e.g., aluminum oxide) and ingested other types (e.g., polystyrene). In some assays, microspheres with very different surface charges or wettabilities were handled similarly, indicating that neither property alone was a qualifier for selection. The differences in surface properties between pairs of microspheres were also considered and used as variables in discriminant analyses. For oysters and mussels, the generated models explained ca. 25% and 72% of the variation in the data, respectively. In both models, wettability was more important than charge in classifying data into their correct group (rejected, preferentially ingested, or not selected). Results from this study support the idea that non-specific physicochemical interactions can play a role in mediating selection in suspension-feeding bivalves. © 2013 Elsevier B.V. All rights reserved. 1. Introduction In estuarine systems, macrobenthic biomass often is dominated by particle-feeding molluscs (see reviews by Dame, 1996; Russell-Hunter, 1983). Suspension-feeding bivalves in particular play a major role in nu- trient cycling, seston modification, and the structuring of benthic food webs (Asmus and Asmus, 1991; Bayne and Newell R.C., 1983; Dame, 1996; Langdon and Newell R.I.E., 1990; Ward and Shumway, 2004). Bi- valves are exposed to large amounts of particulate matter that includes both nutritious and non-nutritious particles (Newell R.C., 1965; Owen, 1966). Consequently, particular attention has been focused on the mech- anisms of feeding in bivalve molluscs. The particle-selection capabilities of bivalves that allow for maximal energy and nutrient uptake have been elucidated in several studies. For example, some bivalves have been shown to: a) discriminate between different algal species (Bougrier et al., 1997; Lesser et al., 1991; Shumway et al., 1985, 1997); b) exhibit strong selection in favor of living particles (Beninger et al., 2007; Kiørboe and Møhlenberg, 1981; Newell R.I.E. and Jordan, 1983; Ward et al., 1997); and c) preferentially ingest particles based upon nutrient content (Bayne et al., 1977; Kiørboe and Møhlenberg, 1981; Levinton et al., 2002; MacDonald and Ward, 1994; Newell R.I.E. and Jordan, 1983; Ward et al., 1997). The exact mechanisms used by suspension-feeding bivalves to determine which particles are ingested and which are rejected as pseudofeces, however, are still unknown. The process of pre-ingestive particle sorting by suspension-feeding bivalves can be described as either passive or active (see reviews by Jørgensen, 1996; Ward and Shumway, 2004). Active selection would be dependent upon a chemosensory response by the cilia or feeding organs to feeding stimuli (Ward and Shumway, 2004), whereas, passive selection is dependent upon the physicochemical interactions between the particles and the feeding organs, with factors such as particle size and shape possibly serving as important contributors to sorting (e.g., larger particles preferentially selected over smaller parti- cles, see Bayne et al., 1977; Riisgård, 1988). Recent work by Pales Espinosa et al. (2009, 2010a, 2010b) has provided evidence for passive selection in bivalves based upon the specific chemical interaction Journal of Experimental Marine Biology and Ecology 446 (2013) 320–327 ⁎ Corresponding author. Tel.: +1 860 405 9062. E-mail address: maria.rosa@uconn.edu (M. Rosa). 0022-0981/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jembe.2013.05.011 Contents lists available at SciVerse ScienceDirect Journal of Experimental Marine Biology and Ecology journal homepage: www.elsevier.com/locate/jembe