Microbial dynamics in coastal waters of East Antarctica: Plankton production and respiration

Abstract

The rates of plankton community production and respiration were determined from in vitro changes in dissolved inorganic carbon and dissolved oxygen and the incorporation of NaH14CO3 at a coastal site in East Antarctica between 16 December 1993 and 12 February 1994. The breakout of seasonal fast ice was associated with a succession of dominant phytoplankton from Cryptomonas to Phaeocystis to a diatom assemblage. Gross production reached 33 mmol C m-3 d-1 and 14C incorporation peaked at 24 mmol C m-3 d-1 on 23 January 1994, at the time of the chlorophyll a maximum (22 mg chl a m-3). Dark community respiration reached its maximum (13 mmol C m-3 d-1) 4 d later. Photosynthetic rates calculated from 14C incorporation were significantly lower (17 to 59%) than rates of gross production. The derivation of plankton processes from changes in both dissolved oxygen and dissolved inorganic carbon allowed the direct measurement of photosynthetic and respiratory quotients. A linear regression of all data gave a photosynthetic quotient of 1.33 ± 0.23 and a respiratory quotient of 0.88 ± 0.14. Concurrent determinations of bacterial, heterotrophic dinoflagellate, nanoflagellate and ciliate respiration could account for 15 to 58 % of measured dark community respiration. This study has improved the sparse data set of plankton respiration measurements, confirmed that heterotrophic respiration is a significant process in the carbon flux of coastal Antarctic waters and achieved a first apportionment of community respiration to the major microbial groups in this region.