Trophic relationships between a Patagonian gastropod and its epibiotic anemone revealed by using stable isotopes and direct observations

Abstract

The carnivorous snail Adelomelon ancilla usually carries, attached to its shell, the anemone Antholoba achates, which also lives attached to hard substrates in the same area. Interaction between both species was studied by stable isotopes analyses (SIA), direct observations, and analysis of gut contents. Results did not show evidences of dietary overlap between anemones and snails. A. ancilla consumed mainly bivalves and secondarily gastropods. The diet of A. achates involved sea urchins and echiurids as main prey. The trophic niches of anemones and snails did not overlap; the species had similar d15N values but differences in their d13C values. Sessile and epibiotic anemones also showed differences in their d13C means, revealing access to different resources. Whereas SIA provided information on trophic relationships and structure, observation of feeding events provided details of prey utilization patterns. Combining direct and indirect approaches helps to overtake method weaknesses and greatly improve dietary descriptions.