Elevation‐mediated cold water refugia in subalpine lakes

Abstract Research on climate change refugia in aquatic systems frequently emphasizes cold‐water habitats and resistance to increasing temperature. Higher‐elevation locations are often identified as important for preserving conditions suitable for cold‐water organisms or communities. However, this concept remains understudied in lentic compared to lotic systems, even as lakes variably experience pronounced climate‐related impacts including ice loss and higher temperatures. Lake responses to climate depend on characteristics such as landscape position, but the role of elevation is not well‐documented and associated biological responses are unclear. Here, we describe spring ice and thermal dynamics in small remote lakes in Maine, USA, ranging from 76 to 955 m above sea level, and how temperature influences zooplankton phenology and community composition. Ice persisted on average 8 days longer in high‐elevation (>500 m) lakes and, after ice breakup, high‐elevation lakes warmed faster (0.3°C/day) than low‐elevation lakes (0.2°C/day), and reached maximum temperatures 45 days earlier on average. Zooplankton phenology was driven by water temperature, but zooplankton taxa varied in response to lake conditions, shaping different zooplankton assemblages in high‐ and low‐elevation sites. This suggests that refugial high‐elevation lakes with prolonged ice and cold spring conditions could present an important regional conservation priority.