Taxon-specific contributions to silica production in natural diatom assemblages

Abstract

The metabolic activity and growth of phytoplankton taxa drives their ecological function and contribution to biogeochemical processes. We present the first quantitative, taxon-resolved silica production rates, growth rates, and silica content estimates for co-occurring diatoms along two cross-shelf transects off the California coast using the fluorescent tracer 2-(4-pyridyl)-5-((4-(2-dimethylaminoethylaminocarbamoyl)methoxy)phenyl)oxazole, and confocal microscopy. Taxon contribution to total diatom community silica production was predominantly a function of the surface area (SA) of new frustule that each taxon created as opposed to cell abundance or frustule thickness. The influential role of SA made large diatoms disproportionately important to community silica production over short time scales (< 1 d). In some cases, large taxa that comprised only ∼ 15% of numerical cell abundance accounted for over 50% of total community silica production. Over longer time scales relevant to bloom dynamics, the importance of SA declines and growth rate becomes the dominant influence on contribution to production. The relative importance of SA and growth rate in relation to silica production was modeled as the time needed for a smaller, faster-growing taxon to create more SA than a larger, slower-growing taxon. Differences in growth rate between the taxa effected the model outcome more than differences in SA. Shifts in relative silica production among taxa are time restricted by finite resources that limit the duration of a bloom. These patterns offer clues as to how taxa respond to their environment and the consequences for both species succession and the potential diatom contribution to elemental cycling.