Impact of early food input on the Arctic benthos activities during the polar night
Résumé
In Arctic areas where benthic primary production does not occur or is not sufficient, the benthos depends on episodic events of food inputs from overlying waters, in particular spring ice algal and phytoplankton blooms. Climate change is expected to lead to earlier ice melts and subsequently to earlier spring blooms and food inputs to the benthos. The goal of the present study was to characterize benthic community structure and activities during the polar night in Rijpfjorden, a high Arctic fjord from Svalbard, and to assess experimentally how earlier climate-induced food inputs can impact these benthic activities. Two concentrations of freeze-dried phytoplankton were added to intact sediment cores, while additional control cores did not receive food addition. Sediment oxygen demand (SOD), nutrient fluxes, bioturbation coefficients (as indicator of benthic activities) and contents of organic matter and pigments in sediments were measured at the beginning of the experiment and 9 days after the addition. In the initial polar night conditions, SOD was similar to 4.2 mmol O-2 m(-2) d(-1), bioturbation coefficients were null for biodiffusion and 1.08 y(-1) for bioadvection, and benthic biomass was 1.36 g 0.1 m(-2). In the cores with food addition, the phytoplankton added was quickly consumed, and after 9 days, SOD and bioturbation were higher in the food treatments compared with the control cores, both being higher with higher food concentration. This study documented a clear and quick response in benthic activities following the food input, suggesting that in winter/early spring, Arctic benthos may depend on early food inputs for its activities. Climate-induced changes in food supply to the seafloor could have drastic consequences for the benthic ecosystem functioning.