Roach (Rutilus rutilus) live in lakes and partly migrate into freshwater tributaries in winter. When most of the population migrates out of the lakes, zooplankton can thrive and control the abundance of phytoplankton, keeping the lake in a clear-water state. However, when most roach stay in the lakes over winter, they feed on zooplankton, reducing its abundance such that phytoplankton can become overabundant and force the lake into a turbid state. This image relates to a paper that appeared in the 4 April, 2014, issue of Science, published by AAAS. The paper, by Silke Bauer at Swiss Ornithological Institute in Sempach, Switzerland, and colleagues was titled, "Migratory Animals Couple Biodiversity and Ecosystem Functioning Worldwide."