Feeding Ecology and Radular Morphology of the Freshwater Limpet Ferrissia fragilis

Abstract

The understory diatom species of Epithemia made up nearly 55% of the diet of the freshwater limpet Ferrissia fragilis, while these same diatom species made up <20% of the epiphyton assemblage on Nuphar leaves occupied by limpets. Furthermore, the larger, upright overstory diatom species had relatively low electivity values. The apparent selection of understory diatom species by Ferrissia may be a function of both shell morphology and the radular architecture. The close-fitting limpet shell may serve to push the larger upright and stalked diatom cells aside, and the small stout teeth of the radulae, as revealed by scanning electron microscopy, scrape the remaining adnate diatom cells. Observations also indicated that Ferrissia avoided clumps of filamentous green algae and large clusters of stalked diatoms. This study provides evidence for resource partitioning of different growth forms of epiphytic algae by gastropod species that occupy the same submerged macrophytes. It may also imply that vacant niches, containing adnate algal species, are present in those freshwater habitats that lack grazers like Ferrissia.