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COLONY SIZE OF PHAEOCYSTIS ANTARCTICA (PRYMNESIOPHYCEAE) AS INFLUENCED BY ZOOPLANKTON GRAZERS1
Authors:Kam W Tang  Walker O Smith Jr  David T Elliott  Amy R Shields
Institution:1. Virginia Institute of Marine Science, College of William and Mary, Gloucester Point, Virginia 23062, USA;2. Author for correspondence: e‐mail .;3. Present address: USEPA, National Risk Management and Research Laboratory, Ada, Oklahoma 74820, USA.
Abstract:The haptophyte Phaeocystis antarctica G. Karst. 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 Phaeocystis globosa suggest that colony formation and enlargement are defense mechanisms against small grazers. To test if a similar grazer‐induced morphological response exists in P. antarctica, we conducted incubation experiments during the austral summer using natural P. antarctica and zooplankton assemblages. Dialysis bags that allowed exchange of dissolved chemicals were used to separate P. antarctica and zooplankton during incubations. 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 d incubation. The estimated colonial‐to‐solitary cell carbon ratio was significantly higher in the grazing treatment. These results suggest that P. antarctica colonies would grow larger in the presence of indigenous zooplankton and skew the carbon partitioning significantly toward the colonial phase. While these observations show that the colony size of P. antarctica was affected by a chemical signal related to grazers, the detailed nature and ecological significance of this signal remain unknown.
Keywords:chemical signal  colony  grazing  Phaeocystis  Southern Ocean
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