Light and nutrient effects on the settling characteristics of the sea ice diatom Nitzschia frigida

Abstract

Sea ice-algae contribute significantly to Arctic primary production and play an important role in the life histories of planktonic and benthic consumers after the algae are released from the sea ice habitat. Following export from the ice, the extent to which fresh algal material is available to planktonic or benthic consumers is dependent on residence time in the water column, initially related to particle settling rate. Laboratory experiments using isolated Nitzschia frigida, a common sea ice diatom, were conducted to ascertain the effects of nutrient (N, P, and Si) and light limitation on settling characteristics of the algal material. While settling characteristics of N- and P-limited cultures were not significantly different from controls grown under light and nutrient-replete conditions, significant differences from the controls were found for light and Si limitation. Differences between treatments were evidenced by changes in the proportion of each population that had particular settling rates, rather than by changes in the range of settling rates measured within a treatment. Thus, fast (> 20 m d-1) and slow-sinking particles (< 2 m d-1) were found in all cultures, but compared to the controls, a larger percentage of fast-sinking particles were observed under Si limitation while a larger percentage of slow-sinking material was observed under light limitation. While N. frigida is just one member of the sea ice algal assemblage, its prevalence in Arctic land-fast sea ice means these results may be representative of the broader Arctic nearshore ice-algae community. As such, abiotic conditions within Arctic sea ice, such as nutrient availability and depth of overlying snow (which affects the light field in the ice), could influence the amount of algae-derived material available to different components of the underlying marine food web.