Food webs in acidic streams

Posted on October 1, 2014

Freshwater systems in many parts of the world, especially in Europe, North America, China and India, have been drastically altered by industrial acidification. Many studies have recorded reductions in biodiversity and species abundance in acidified waters, but the food web implications of acidification are less well understood. Macroinvertebrate communities in 20 streams across the U.K. were sampled in spring (April-May). The streams varied widely in terms of pH (5.0 – 8.4). Benthic diatoms were sampled by removing the biofilm from rocks and stones and food-web relationships were examined by stable isotope analysis of invertebrates and by examining the contents of their guts. Multivariate techniques (correspondence analyses) were used to compare the invertebrate communities. As the pH of stream water increased, there were trends of increase in the density and diversity of diatoms, the concentration of chlorophyll in biofilms, the richness and density of macroinvertebrate communities, and the complexity of the food web. Generalist consumers of algae and detritus, especially stoneflies, were found in most streams, and were most common in acidic streams that had lost specialist acid-sensitive grazers (e.g., mayflies, snails). The ability of these generalists to use detritus as well as algae may stabilise the dynamics of streams recovering from acidification, resist invasions by specialist algal grazers, and help to explain the slow recovery of biological communities in acidified fresh waters.

Reference: Layer, K., Hildrew, A.G. & Woodward, G. 2013. Grazing and detritivory in 20 stream food webs across a broad pH gradient. Oecologia 171:459–471.