Do food quantity and quality affect food webs in streams polluted by acid mine drainage?
2013
Hogsden, Kristy L. | Winterbourn, Michael J. | Harding, Jon S.
Food influences the structure of consumer communities; however, in polluted streams food resources may be severely reduced and act as an additional stressor. We examined the quantity and quality of basal resources and prey items for invertebrate consumers in 12 streams along an acid mine drainage (AMD) gradient (pH range: 2.7–7.1) and characterised their diets using stable isotope and gut content analyses. Algal and detrital resource quantity (biomass) and quality (C:N ratio) did not differ significantly along the gradient, except algal C:N, which was lower in highly stressed and circumneutral streams. Furthermore, availability, size and diversity of animal prey decreased significantly with increasing stress. Most primary consumers were generalist feeders, but algae became increasingly common in their diets as pH increased. Predators were opportunistic and consumed prey that reflected locally abundant taxa. Generally, these were small-bodied chironomids in highly stressed streams and larger-bodied prey (mayflies, caddisflies, stoneflies) in moderately stressed and circumneutral streams. Our results indicated that acidity and metal toxicity were the primary stressors of communities in streams affected by AMD and that food quantity was unlikely to be limiting for primary consumers. However, food availability may be an additional stressor affecting predators in streams receiving AMD.
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