Recent Changes in the Zooplankton Communities of Arctic Tundra Ponds in Response to Warmer Temperatures and Nutrient Enrichment

Abstract

Warming is altering Arctic freshwater ecosystems, enriching the water column, increasing primary productivity and shifting the composition, dominance and the timing of emergence and reproduction of zooplankton communities. Historic data from arctic tundra ponds near Utqiaġvik, AK have given us valuable insight into changes that have occurred in recent times. A change of dominance from cyclopoid copepods to Daphnia middendorffiana has occurred over a 40 year period. Daphnia are more common, abundant and larger, which may be explained by increased primary productivity stimulated by nutrient release from permafrost thaw. Copepods and fairy shrimp emerged earlier from the overwintering states, which may be due to warmer spring temperatures. These trends are supported by both lab experiments and regional surveys of enriched ponds in urban and thermokarst areas, which confirm that warming and enrichment are a driver of change in tundra pond zooplankton communities.

In nutrient addition experiments, nutrient additions and the addition of permafrost sediment affected the dominance of algal groups and the growth and reproduction of Daphnia. In water sourced from a tundra pond, phosphorus clearly enhanced Bacillariophyceae density while nitrogen enhanced Cyanophyta abundance. Relative dominance of Daphnia increased due to the presence of algae enriched by phosphorus, and especially that co-enriched from thawing permafrost in our experiments. This further supports previous work showing that arctic Daphnia depend on benthic algae for their nutrition.

Enrichment by human activities, but particularly thermokarsting, are causing substantial changes to the tundra pond environment and their associated zooplankton communities. In a survey of ponds along a gradient including thermokarst, urban ponds, and reference sites, nutrients increased algal biomass and total abundance of zooplankton especially, Daphnia middendorffiana and cyclopoid copepods. This space-for-time subtitution lends support to nutrient enrichment as the driver of increased Daphnia biomass over time. Some new taxonomic records for the region were observed: Bosmina longirostris and harpacticoid copepods. Both urban enrichment and thermokarsting will have important implications for both primary and secondary producers with future warming.

Both historic changes in tundra ponds, as well as observed drivers in thermokarst and urban ponds, can gave us an idea of the future changes due to warming and enrichment in the other ponds in the region. These changes at the level of the zooplankton may have important impacts on other components of the Arctic food web, including algae, as well as upper trophic levels that depend on zooplankton for food. Given that unprecedented warming is occurring, and likely continue into the future, these unique ecosystems must continue to be observed to predict, understand and model future alterations to Arctic ecosystems.