Macroinvertebrates in the diet of the apple snail Pomacea canaliculata in its native range

Abstract

The study of diet and how a species obtains food is relevant to understand its rolewithin natural environments. The apple snail Pomacea canaliculata (Lamarck, 1822) isa freshwater dweller that primarily consumes aquatic macrophytes and detritus but alsoincorporates resources of animal origin in its diet. Our aim was to investigate the ingestion ofmacroinvertebrates by P. canaliculata in four watercourses from its native range by analyzingits digestive contents. The frequency of occurrence of animal remains in the digestivecontents of P. canaliculata snails was 68.50% across diff erent seasons, with values of morethan 50% in each of the watercourses studied. The spring-summer contents showed highfrequencies of animal remains, whereas in autumn they were recorded only in 10% of thecontents from one of the watercourses. The macroinvertebrates ingested belonged to sixdiff erent insect orders, crustaceans, mites, bivalves, and gastropods. The frequencies ofoccurrence were higher for arthropods than for mollusks in two watercourses and similar inthe other two. In two watercourses, the relative abundances of mollusks were higher thanthose of arthropods and the opposite was true in the other two. The number of individualsingested by an average P. canaliculata was highest for the snail Heleobia parchappii, followedby arthropods, H. parchappii eggs, and the snails Physella acuta and Chilina parchappii.Most ingested macroinvertebrates were small, slow or with little or no mobility, such as snailsand case-bearing insects. Arthropods able to swim or to swiftly escape, such as Amphipodaand nymphs of Odonata and Ephemeroptera, were not detected at all in the digestivecontents. Ingestion of macroinvertebrates appears to be opportunistic and even accidentaland probably depends more on their microhabitats or behavior than on preferences of P.canaliculata. Notwithstanding, the high frequency of ingestion observed on some species ofsnails could have a signifi cant negative effect on the abundance of their populations.