An experimental investigation of interactions in snail-macrophyte-epiphyte systems |
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Authors: | G J C Underwood J D Thomas J H Baker |
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Institution: | (1) School of Biology, University of Sussex, Falmer, BN1 9QG Brighton, Sussex, UK;(2) N.E.R.C., Polaris House, North Star Avenue, SN2 1EU Swindon, Wiltshire, UK;(3) Department of Biology, University of Essex, CO4 3SQ Colchester, Essex, UK |
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Abstract: | Summary An experimental investigation under field conditions of enclosures containing freshwater pulmonate snails, the macrophyteCeratophyllum demersum and epiphytes, produced evidence of beneficial interactions.Ceratophyllum growth, measured in terms of stem length, numbers of leaf-nodes and growing tips and leaf survival was significantly enhanced
in the presence of snails. This effect was attributed to the increased availability of plant nutrients of snail origin, such
as phosphates and ammonia, as well as to the snails' action as “cleaning symbionts” in reducing the density of bacterial and
algal epiphyton potentially deleterious to macrophytes. Principal component analysis revealed both seasonal and treatment
effects of snail grazing on algal epiphyton. Small adnate algal species (e.g.Cocconeis placentula) survived grazing and benefited from the removal of larger, competitor, species. Snail densities increased in all treatments,
despite high (86%) juvenile mortality. It is concluded that freshwater pulmonate snails are strong interactors in lentic habitats,
enhancing the growth ofCeratophyllum and producing characterisic epiphyte communities. This benefits not only the snails, but also the plants and epiphytes that
are associated with them. Thus the interactions between these component parts of the community can be considered as mutualistic. |
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Keywords: | Freshwater snails Macrophytes Grazing Epiphytes Mutualism |
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