Macroinvertebrates in the Diet of the Apple Snail Pomacea canaliculata in Its Native Range

Abstract

ABSTRACT The study of diet and how a species obtains food is relevant to understand its role within natural environments. The apple snail Pomacea canaliculata (Lamarck, 1822) is a freshwater dweller that primarily consumes aquatic macrophytes and detritus but also incorporates resources of animal origin in its diet. Our aim was to investigate the ingestion of macroinvertebrates by P. canaliculata in four watercourses from its native range by analyzing its digestive contents. The frequency of occurrence of animal remains in the digestive contents of P. canaliculata snails was 68.50% across different seasons, with values of more than 50% in each of the watercourses studied. The spring-summer contents showed high frequencies of animal remains, whereas in autumn they were recorded only in 10% of the contents from one of the watercourses. The macroinvertebrates ingested belonged to six different insect orders, crustaceans, mites, bivalves, and gastropods. The frequencies of occurrence were higher for arthropods than for mollusks in two watercourses and similar in the other two. In two watercourses, the relative abundances of mollusks were higher than those of arthropods and the opposite was true in the other two. The number of individuals ingested by an average P. canaliculata was highest for the snail Heleobia parchappii, followed by 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 snails and case-bearing insects. Arthropods able to swim or to swiftly escape, such as Amphipoda and nymphs of Odonata and Ephemeroptera, were not detected at all in the digestive contents. Ingestion of macroinvertebrates appears to be opportunistic and even accidental and probably depends more on their microhabitats or behavior than on preferences of P. canaliculata. Notwithstanding, the high frequency of ingestion observed on some species of snails could have a significant negative effect on the abundance of their populations.