Detritus from Ice and Plankton Algae as an Important Food Source for Macroinfaunal Communities in the Canadian Arctic

Abstract

Most deep-sea organisms feed on the organic matter produced in surface waters and settleon the seafloor. In polar regions, sea ice algal detritus and phytoplankton detritus are the main foodsources for benthic fauna that reach the seafloor in pulses. Climate change affects the extension andduration of sea ice cover, which may affect the quantity and quality of food reaching the seafloor,resulting in less ice algae and more phytoplankton biomass. We conducted onboard pulse-chaseexperiments using sediment cores collected from Baffin Bay, Amundsen Gulf, and the Beaufort Sea tostudy how macroinfaunal communities in the Canadian Arctic use both food sources. Dual-labeled(13C and 15N) diatoms, Thalassiosira nordenskioeldii (phytoplankton treatment) and Synedra hyperborea(ice algae treatment), were used as tracers of food consumption by macroinfaunal groups. Communitystructure was analyzed in each region and differences were found among sites. The total uptakeof both food sources was higher in Baffin Bay; the macroinfaunal biomass was the highest, withfacultative filter/surface-deposit feeders accounting for more than 70% of the total biomass. TheBaffin Bay station was the only location where there were notable variations in the biomass-specificuptake of ice algae and phytoplankton detritus by the bivalves and polychaetes, as well as by thecommunity as a whole. At the same time, both food sources were consumed in equal quantities atthe Amundsen Gulf and Beaufort Sea stations. This suggests that ice algae are not preferentiallyuptaken, and macroinfaunal communities may be resilient to a decrease in ice algal input to theseafloor inflicted by sea ice reduction.