Environmental and habitat controls on non-marine ostracod distribution in Greenlandic Arctic lakes

The Arctic is warming almost four times faster than the global average. Lakes in the Arctic are a prominent feature of the landscape and are consequently undergoing limnological and ecological change such as shifts in algal productivity, water column mixing depths, and ice persistence. Most recently, the nutrient-colour paradigm has been associated with extensive loss of benthic habitat. Ostracods (small aquatic crustaceans) are a significant contributor to the benthic biomass of shallow to mid-depth lakes (< 20 m) and there is great potential to use fossil ostracods to reconstruct past environmental change and predict future ecosystem states in these lake-rich regions. However, relative to mid-latitude regions, little is known of the ecological traits of ostracods in the Arctic. Here we present the first systematic survey of ostracod species and ecological preferences for the Kangerlussuaq region of southwest Greenland, the largest ice-free margin of Greenland. Twenty-four lakes (< 16 m deep) were surveyed in July 2021 in a SW-NE gradient from the Greenland Ice Sheet. Electrical conductivity in the lakes ranged from 0.01 to 4.1 mS cm−1. All lakes were ultra-oligotrophic to mesotrophic; soluble reactive phosphorus ranged from 1.9 to 49.7 µg L−1 and nitrate concentrations from below detection limit to 12.3 µg L−1. In total, thirteen species of ostracods were recorded across the study lakes. Candona candida is a generalist species in the Kangerlussuaq region, being present in deeper lakes and at the higher end of the bioavailable phosphorus and nitrate gradients. These traits suggest that C. candida will become abundant in the Greenlandic ostracod fauna, and potentially across the Arctic. For some species, particularly Cypris pubera, bioavailable nutrient concentrations are a dominant control on distribution. Nutrient status of water appears to be a significant control on ostracod presence and abundance and should be included in future ecological studies globally.