Changes in biofilms induced by flow regulation could explain extinctions of aquatic snails in the lower River Murray, Australia

• Published in: Hydrobiologia 1997-03, Vol.347 (1-3), p.97-108
• Main Authors: SHELDON, F, WALKER, K. F
• Format: Article
• Language: English
• Subjects: Algae; Animal and plant ecology; Animal populations; Animal reproduction; Animal, plant and microbial ecology; Animals; Biofilms; Biological and medical sciences; Biomass; Demecology; Detritus; Food resources; Freshwater; Fundamental and applied biological sciences. Psychology; Gastropoda; Mollusks; Nutritive value; Protozoa. Invertebrata; River ecology; Rivers; Turbidity; Water levels; Weirs
• ISSN: 0018-8158; 1573-5117
• DOI: 10.1023/A:1003019302094

Notopala sublineata, Notopala hanleyi(Viviparidae) andThiara balonnensis (Thiaridae) are prosobranchgastropodsthat were once abundant in the lower River Murray. These andothersnail taxa have declined markedly over the last 50 years,coinciding with increased flow regulation by dams and weirs.Inthis paper we speculate that the decline may be linked tochangesin the nature of food resources. Before regulation, most ofthebiofilm biomass in the lower Murray probably was microbial, asfluctuating water levels and high turbidity would havemaintainedthese communities in a state of early succession. Bystabilisingseasonal water levels, we suggest that regulation has promotedthegrowth of filamentous algae, perhaps at the expense ofbacteria.Evidence from gut and faecal pellet analysis, and fromanalysis ofcarbon stable-isotopes, suggests that the gastropod taxa aredetritivores, feeding mainly on amorphous organic detritus.Algaehave a relatively high C:N ratio (low nutritional value) andmay bean inadequate food to maintain female growth and reproduction,especially in viviparous snails.[PUBLICATION ABSTRACT]