Vulnerability of rotifers and copepod nauplii to predation by Cyclops kolensis (Crustacea, Copepoda) under varying temperatures in Lake Baikal, Siberia

As lakes warm worldwide, temperature may alter plankton community structure and abundance by affecting not only metabolism but also trophic interactions. Siberia’s Lake Baikal presents special opportunity for studying shifting trophic interactions among cryophilic zooplankton species in a rapidly warming lake. To understand how warming may affect trophic interactions among plankton, we studied predator–prey relationships of a copepod predator (Cyclops kolensis) with three prey types: two rotifer species (Gastropus stylifer and Keratella cochlearis) and copepod nauplii. We hypothesized that the less evasive Gastropus and Keratella would be more susceptible to predation than nauplii. We exposed a starved predator to individuals of each prey type and observed encounters, ingestions, and escapes. Contrary to our hypothesis, Keratella were consumed at lower rates than nauplii, due to higher probability of ingestion after encounter with nauplii. In a second experiment, we assessed how predation varied across a thermal gradient, confining all three prey types and one starved predator at 5° temperature increments (5–20°C). Predation outcomes mirrored observational feeding trials, and predation outcomes were independent of temperature. Rotifers’ relatively high reproductive rate may present a mechanism to withstand predation should copepod’s preferred nauplii prey become less abundant in a warmer Baikal.