Are Hotspots Always Hotspots? The Relationship between Diversity, Resource and Ecosystem Functions in the Arctic

The diversity-ecosystem function relationship is an important topic in ecology but has not received much attention in Arctic environments, and has rarely been tested for its stability in time. We studied the temporal variability of benthic ecosystem functioning at hotspots (sites with high benthic boundary fluxes) and coldspots (sites with lower fluxes) across two years in the Canadian Arctic. Benthic remineralisation function was measured as fluxes of oxygen, silicic acid, phosphate, nitrate and nitrite at the sediment-water interface. In addition we determined sediment pigment concentration and taxonomic and functional macrobenthic diversity. To separate temporal from spatial variability, we sampled the same nine sites from the Mackenzie Shelf to Baffin Bay during the same season (summer or fall) in 2008 and 2009. We observed that temporal variability of benthic remineralisation function at hotspots is higher than at coldspots and that taxonomic and functional macrobenthic diversity did not change significantly between years. Temporal variability of food availability (i.e., sediment surface pigment concentration) seemed higher at coldspot than at hotspot areas. Sediment chlorophyll a (Chl a) concentration, taxonomic richness, total abundance, water depth and abundance of the largest gallery-burrowing polychaete Lumbrineris tetraura together explained 42% of the total variation in fluxes. Food supply proxies (i.e., sediment Chl a and depth) split hot- from coldspot stations and explained variation on the axis of temporal variability, and macrofaunal community parameters explained variation mostly along the axis separating eastern from western sites with hot- or coldspot regimes. We conclude that variability in benthic remineralisation function, food supply and diversity will react to climate change on different time scales, and that their interactive effects may hide the detection of progressive change, particularly at hotspots. Time-series of benthic functions and its related parameters should be conducted at both hot- and coldspots to produce reliable predictive models

Changes in Arctic Benthos

The shift towards a seasonally ice-free Arctic Ocean raises many questions related to the future of productivity and function of Arctic ecosystems. The highly productive marginal ice zone is dragged closer towards the center of the Arctic, and the ongoing thinning of sea ice and increased light penetration to the surface ocean may change spatio-temporal patterns of under- ice productivity. As under-ice processes are hard to monitor we study the dynamics on (and in) the Arctic seafloor, particularly the macrobenthos, as a proxy for pelagic change. We use biological trait analysis (BTA) to study the benthic functions and responses as this method links species, environment and ecosystem processes (Bremner 2005). Although benthos data from the Arctic and especially from the Arctic deep sea are scarce, international cooperation enables us to compile a dataset ranging over the past twenty years up to today. Based on this dataset we show that benthic functional traits like secondary production are correlated to Arctic sea ice and its associated dynamics. We give a regional example where benthic community functions have changed already over the last twenty years and highlight the areas of the Arctic Ocean that are most prone to these effects. Finally we want to stress the importance of international cooperation in the process of integrating existing data and knowledge to build up a spatially explicit Arctic trait database. Such a database would provide the scientific base to classify the Arctic into clearly defined “eco-function” regions. This functional atlas can then be used by the scientific community to correlate observed environmental trends and predict upcoming changes in ecosystem functioning accordingly

Revisiting the footprints of climate change in Arctic marine food webs: An assessment of knowledge gained since 2010

In 2011, a first comprehensive assessment of the footprints of climate change on Arctic marine ecosystems (such as altered distribution ranges, abundances, growth and body conditions, behaviours and phenologies, as well as community and regime shifts) was published. Here, we re-assess the climate-driven impacts reported since then, to elucidate to which extent and how observed ecological footprints have changed in the following decade (2011 to 2021). In total, 98 footprints have been described and analysed. Most of those impacts reported in the 2011 assessment are reconfirmed and can, hence, be assumed as continuing trends. In addition, novel footprints (behavioural changes, diet changes, altered competition and pathogen load) are described. As in 2011, most reported footprints are related to changes in distribution ranges, abundances, biomass and production. Range shifts have mostly been observed for fish species, while behavioural changes have mainly been reported for mammals. Primary production has been observed to further increase in Arctic seas. The footprints on pelagic herbivores, particularly the key species Calanus spp., are less clear. In comparison to 2011, more complex, cascading effects of climate change, such as increased bowhead whale body conditions due to increased primary production, have been reported. The observed footprints, and the trends that they indicate, strongly suggest that due to further northward range shifts of sub-Arctic and boreal species Arctic seas are likely to experience increasing species richness in the future. However, a tipping point may be reached, characterized by subsequent biodiversity decline, when Arctic-endemic species will go extinct as ocean warming and/or acidification will exceed their physiological adaptation capacity.Overall, the future Arctic Ocean will very likely experience increasing numbers and intensities of climate-change footprints