Dissolved and particulate DNA dynamics during a spring bloom in the Antarctic Peninsula region, 1986–1987

Abstract

Dissolved and particulate DNA (D-DNA and P-DNA, respectively) concentrations were measured at 69 stations in a 25,000 km 2 section of Bransfield Strait, during the austral summer period (December 1986 to March 1987). During the development of the seasonal spring bloom of phytoplankton (December and January), surface water P-DNA (0.2–202μm) exhibited an order-of-magnitude concentration gradient, from values of ≥25 μg DNA I −1 in the productive coastal water near the northern end of Gerlache Strait to ≥4 μg DNA l −1 in the more oligotrophic waters of Drake Passage. P-DNA concentrations were highly correlated with other biochemical indices of microbial biomass (e.g. chlorophyll α and ATP). A majority (≥50%) of the P-DNA was contained in the 0.2–20 μm size category. Estimates derived from DNA:ATP ratios and from direct measurements of bacterial cell abundance suggest that most of the P-DNA during the spring bloom period was associated with living phytoplankton cells, with little, if any, non-living, P-DNA. In contrast to these characteristics of the spring bloom period. P-DNA during post-bloom conditions (March) was low (4–6 μg DNA l −1) and nearly constant throughout our study area, was nearly exclusively (≥80%) contained in the 0.2–20 μm size category, and was nearly exclusively (≥90%) comprised of non-living DNA. D-DNA was ubiquitously distributed in the near-surface waters throughout the RACER study area in December, with concentrations ranging from 6 to 16 μg DNA l −1. However, there was no spatial correlation with either microbial biomass or microbial productivity. By January, surface water D-DNA concentrations had decreased to values ≤10% of the December values (≤1 μg DNA l −1 and by the February to March sampling periods, D-DNA was undectetable throughout our study areas (≤0.1 μg DNA l −1). The dynamics of the D-DNA pools were not well correlated with microbial biomass and production. Rather, the seasonal D-DNA distributions appeared to be controlled by the advection of D-DNA enriched water masses across our study area in December, followed by replacement with D-DNA depleted waters. We hypothesize that the early season D-DNA may be derived from microbial communities in melting ice or from diagenesis in shallow benthic habitats. The results of a box model calculation of P-DNA and D-DNA inventories and fluxes in Bransfield Strait suggest that the northern Gerlache Strait is a major exporter of P-DNA, either as a result of horizontal advection or active transport of macrozooplankton populations.