Ecosystem age drives food web architecture of glacier retreat-formed fishless ponds in Greenland

Arctic ecosystems are undergoing major changes as a result of climate change that in many cases results in habitat loss for many species. However, glacial retreat also creates new habitats, such as lakes and ponds, providing an opportunity to test how communities and food webs assemble. Here, we studied the topology of the food webs and analyzed potential drivers such as environmental variables in 16 fishless ponds of contrasting age (8 young < 50 years, 8 old > 150 years) located in an area of rapid glacial retreat on the west coast of Greenland. We tested for differences in beta diversity and nestedness of prey and consumers related to the age class of the ponds. Based on gut content analysis of zooplankton and benthic macroinvertebrates we constructed food webs and investigated the extent to which food web metrics related to pond age and environmental variables. The food items of zooplankton and benthic macroinvertebrates in the young ponds represented a subset of those present in the old ponds' food webs. Food webs of old ponds had higher taxonomic richness, higher linkage density and lower connectance, indicating higher stability. Pond age class was the main explanatory factor for most food web metrics followed by productivity, here assessed by proxies, total nitrogen (TN) and phytoplankton chlorophyll-a (Chl-a). Food webs in old ponds did not show any significant association with environmental factors. In contrast, in young ponds, connectance and trophic niche overlap were significantly related to TN and Chl-a. The different complexity patterns indicate that food web topology in newly created ponds becomes more complex and independent of environmental conditions as ponds age. These differences likely make food webs of young ecosystems more unstable and vulnerable to external disturbances than those of older ecosystems.