while epibiotic associations between macrobenthic invertebrates are common, the role they play in the feeding ecology of intervening species is often incompletely understood. the diets of epibiotic sea anemones allantactis parasitica and their gastropod hosts were analyzed using digestive tract contents, lipid biomarkers and observations of live specimens in an attempt to detect dietary feedback from the facultative association. comparisons were made using symbiotic individuals and asymbiotic counterparts collected at depths of 191-627 m from three neighbouring areas in the northwest atlantic. gastropods carrying one or two epibionts had higher stomach indices than those harbouring three epibionts or no epibiont. the diet of symbiotic gastropods was also more diversified based on stomach contents and lipid analysis. among other things, symbiotic gastropods contained four times more lipids and a greater proportion of sigma n-3 fatty acids. gastrovascular cavity content indices of asymbiotic sea anemones were generally lower than those of symbiotic counterparts. their cavities were more often empty, and their diet less diversified with fewer benthic items, suggesting that foraging of gastropods through the sediments makes more food available to sea anemones living as epibionts. lipid analysis showed some disparities between symbiotic and asymbiotic sea anemones at the regional scale, including in percent phospholipids and in the proportion of certain fatty acids. together these findings indicate that mutual protection against predators leads to prolonged and more efficient foraging for gastropods and increased time spent deployed (feeding) in food-rich areas for sea anemones, thus enabling both partners to fully exploit food resources that may be limited at bathyal depths. (c) 2010 elsevier b.v. all rights reserved.