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Colony Size of Phaeocystis Antarctica (Prymnesiophyceae) as Influenced by Zooplankton Grazers
Citation:
Tang, K. W., W. O. SMITH, Jr., D. Elliott, AND A. R. SHIELDS. Colony Size of Phaeocystis Antarctica (Prymnesiophyceae) as Influenced by Zooplankton Grazers. JOURNAL OF PHYCOLOGY. Blackwell Publishing, Malden, MA, 44(6):1372-1378, (2008).
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Description:
The haptophyte Phaeocystis antarctica is a dominant phytoplankton species in the Ross Sea, Antarctica, and exists as solitary cells and mucilaginous colonies that differ by several orders of magnitude in size. Recent studies with P. globosa suggested that colony formation and enlargement is a defense mechanism against small grazers. To test if a similar grazer-induced morphological response exists in P. antarctica, we conducted incubation experiments at McMurdo Station during the austral summer using natural P. antarctica and zooplankton assemblages. Dialysis bags were used to separate P. antarctica and zooplankton during incubations, but these allowed exchange of dissolved chemicals. Geometric mean colony size decreased by 35% in the control, but increased by 30% in the presence of grazers (even without physical contact) over the 15-day incubation period. Estimated colonial-to-solitary cell carbon ratio was significantly higher in the grazing treatment. These results suggest that a grazing signal from the indigenous zooplankton community could cause P. antarctica colonies to grow significantly larger, and skew the carbon partitioning significantly toward the colonial phase. While these observations support the notion that colony formation and enlargement is a defense mechanism by P. antarctica against grazing, the cost of such mechanism, as predicted by defense theory, remains unknown.
