Carbon partitioning within Phaeocystis antarctica (Prymnesiophyceae) colonies in the Ross Sea, Antarctica

The haptophyte Phaeocystis antarctica Karsten is a dominant species within the seasonal bloom in the Ross Sea. One of the unique characteristics of th is form is that carbon is partitioned between the cells and the colonial ma trix, a relationship that is poorly documented for this region. We combined particulate organic carbon measurements and microscopic analysis of P, ant arctica-dominated samples to assess the contribution of single cells, colon y-associated cells, and mucilage to the carbon concentrations of waters wit h P. antarctica, Two cruises to the Ross Sea were completed, one in austral spring 1994 and one in summer 1995-1996, In 1994 the bloom was dominated b y colonial P, antarctica that contributed up to 96% of the total autotrophi c carbon, whereas in 1995-1996 a mixture of P, antarctica and diatoms occur red. P, antarctica colony volume (V) was related to colonial cell number (N c) by the relationship V = 417 X N-C(1.67). Total colony carbon (C-COL) was calculated as the sum of cell carbon (C-CC) and mucus-related carbon (Chl) . We found the contribution of mucus carbon to be 213 ng C mm(-3) of colony volume. For P, antarctica-dominated assemblages sampled at the peak of the bloom, C, represented a minor fraction (14 +/- 4%) of colony carbon, and d uring early summer conditions C-M was at most 33% of CCOL. This organism pl ays a cardinal role in the carbon cycle of many regions. These results cons train the partitioning of carbon between cellular material and the colony m atrix, information that is necessary to accurately describe the biogeochemi cal, cycles influenced by this species.