Data and code for: Exploring the role of body mass in temperature-driven changes in metabolic rates of Arctic copepods

As Arctic sea temperatures rise and sea ice declines, boreal species are becoming more abundant in these waters. Generally, both inter- and intra-species variations show larger body sizes at higher latitudes and in colder climates. Continued Arctic amplification may lead to shifts in the size and composition of marine plankton, with cascading effects throughout the ecosystem. This study examines the metabolic rates of three common zooplankton species, Calanus finmarchicus, C. glacialis, and Metridia longa, across different temperatures (0, 3, and 6 °C) to understand these dynamics. Results showed a distinct decrease in aerobic scope with rising temperatures for all three copepod species, indicating potential fitness reductions in warmer waters. Larger copepods exhibited higher aerobic scopes than smaller ones at all temperatures; however, this advantage diminished at 6 °C, suggesting that smaller body sizes may confer metabolic benefits at higher temperatures. Conversely, larger sizes are favored in colder waters. These findings help explain the increase of smaller boreal species in warming Arctic seas and why colder Arctic conditions favor larger individuals.