RESEARCH ARTICLE T. Erin Cox Æ Steven N. Murray Feeding preferences and the relationships between food choice and assimilation efficiency in the herbivorous marine snail Lithopoma undosum (Turbinidae) Received: 19 July 2004 / Accepted: 6 October 2005 / Published online: 2 December 2005 Ó Springer-Verlag 2005 Abstract Preference rankings for 13 macrophytes were established for the subtidal herbivorous snail Lithopoma undosum using two-choice laboratory experiments and consumption rates. L. undosum did not discriminate among three kelp foods (Egregia menziesii, Eisenia ar- borea and Macrocystis pyrifera) but ate kelp preferen- tially and more rapidly over all but Ulva spp. among tested macrophytes. Secondary preferences were estab- lished for the red alga Pterocladiella capillacea, followed by the coralline Lithothrix aspergillum, whereas the brown seaweeds Zonaria farlowii and Halidrys dioica and the seagrass Phyllospadix torreyi were the least preferred macrophytes. Fastest consumption rates (1.91 g day 1 ) were measured in trials consisting only of kelp foods. These results indicate that L. undosum exhibits clear feeding preferences even when given less- preferred, non-kelp macrophytes. Using an ash-marker technique, we determined total organic, carbon, and nitrogen assimilation efficiencies (AE%) for six macro- algae used in preference trials. Tested macrophytes were assimilated at different efficiencies but a pattern was not detected between AE (%) and a macrophyte’s position in L. undosum’s preference hierarchy. Highest total or- ganic AEs were found for P. capillacea (61.2%) and H. dioica (59.4%); lowest AEs were detected for E. menziesii (34.9%), a preferred dietary item. Nitrogen was assimilated from red algae with higher efficiencies (74.9–84.3%) than from brown or green algae. These data suggest that the digestive capabilities of L. undosum are better suited for assimilating organic material and nitrogen from less-preferred, non-kelp foods. This sup- ports the hypothesis that factors besides nutritional composition and digestive optimization have played a role in the evolution of feeding preferences in L. undo- sum and probably other herbivorous snails associated with northeastern Pacific kelp beds. Introduction Several species of herbivorous macro-invertebrates have been shown to choose certain macrophyte species as foods over others (Leighton 1966; Vadas 1977; Steinberg 1985; McShane et al. 1995; Wakefield and Murray 1998). Macrophyte characteristics such as morphology (Littler and Littler 1980; Padilla 1985) and the presence of deterrent chemicals (Steinberg 1985; Hay and Fenical 1988; Van Alstyne et al. 1999) influence these choices by affecting the edibility and palatability of potential foods. Because an animal’s performance is based on obtaining sufficient energy and nutrients, the nutritional compo- nents of a food item, in particular its nitrogen content (Mattson 1980; White 1985), also may be important determinants of food choice (Pyke 1984). Most studies (Nicotri 1980; Jensen 1983; McShane et al. 1995; Wakefield and Murray 1998; Arrontes 1999), however, have failed to show a consistent correlation between the nutritional content of consumed macrophytes and their place in a benthic herbivore’s dietary preferences. In the northeastern Pacific and other temperate wa- ters supporting kelp beds, many macro-invertebrate herbivores appear to feed preferentially on kelps over other macrophytes as evidenced by faster rates of kelp consumption (Vadas 1977; Watanabe 1984a) and results of choice experiments (Leighton 1966; Steinberg 1985; Wakefield and Murray 1998). Many molluscan (Schmitt et al. 1983; Watanabe 1984a) and small benthic crusta- cean (Duffy and Hay 1991, 1994) herbivores have low mobility and suffer high predation rates when removed from macrophyte food resources. This relationship Communicated by P.W. Sammarco, Chauvin T. E. Cox (&) Botany Department, University of Hawaii at Manoa, 3190 Maile Way, Room 101, Honolulu, HI 96822, USA E-mail: erincox@hawaii.edu Tel.: +1-808-956-3923 Fax: +1-808-9568389 S. N. Murray Department of Biological Science, California State University, P.O. Box 6850, Fullerton, CA 92834-6850, USA Marine Biology (2006) 148: 1295–1306 DOI 10.1007/s00227-005-0166-3