TITLE:     Changes in phytoplankton assemblages in response to glacial 
	   melting along the Antarctic Peninsula: Alteration in the food 
	   web due to regional warming?
AUTHOR:    MA Moline, H Claustre, TK Frazer, J Grzymski, KL Haberman, & 
	   O Schofield
DATE:      9-13 February 1998
PLACE:     AGU/ASLO, Ocean Sciences Meeting, San Diego, CA
           Poster

ABSTRACT:
  Mean air temperatures along the Antarctic Peninsula have significantly
increased  (2-3 degs C) over the past 50 years, however, the impacts of this
trend on food web dynamics are poorly understood.  As part of the LTER
program, phytoplankton assemblages were monitored off Anvers Island over a
three year period.  Despite large interannual and seasonal fluctuations in the
water column biomass, resulting from variations in meteorologic and hydrologic
conditions, there was a recurrent dominance of cryptophytes during midsummer.
This dominance was shown to correlate with the decreased salinity from glacial
meltwater.  The transition from a system traditionally dominated by diatoms in
the summer to one dominated by crytophytes represents a fundamental decrease
in the average size of water column phytoplankton.  Smaller size classes are
not efficiently grazed by Antarctic krill (Euphausia superba), the key
Antarctic zooplankton species.  Therefore, an increase in cryptophyte
dominance during the summer months has potentially significant implications
for the food web.  Output from a food web model suggest that decreased grazing
efficiency and shifting zooplankton assemblages in response to increased
cryptophyte dominance can decrease carbon available to higher trophic levels
by as much as 42Continued increase in air temperature will likely increase the
duration and spatial extent of glacial meltwater on the shelf and may increase
the importance of cryptophytes in the Antarctic food web and biogeochemical
cycling.