TITLE:     Selective grazing by the Antarctic krill, euphausia superba, in
           mixed phytoplankton assemblages
AUTHOR:    KL Haberman, RM Ross, LB Quetin
DATE:      9-13 February 1998
PLACE:     AGU/ASLO, Ocean Sciences Meeting, San Diego, CA
           Poster

ABSTRACT:
  Antarctic krill are known to exploit phytoplankton blooms in the austral
spring and summer to fuel their growth and reproduction.  While diatoms are
recognized as a primary food source for the krill, the contribution of other
types of phytoplankton to their diet is not well understood.  In particular,
prymnesiophytes (Phaeocystis sp.) and cryptomonads comprise a significant
proportion of the phtyoplankton community in regions of the Antarctic with
high krill biomass.  This study examines whether krill differentially ingest
particular phtyoplankton taxa within mixed assemblages.
  We conducted laboratory grazing experiments on field-collected and cultured
phytoplankton mixtures to compare the ingestion of each phytoplankton type
relative to its presence within the mixture.  HPLC analysis of taxonomic
marker pigments from water samples collected during the experiments showed
that diatoms were selectively grazed over cyrptomonads and Phaeocystis.
This was true even when Phaeocystis was in its colonial phase, with colony
sizes comparable to the diatoms.
  To further investigate whether krill significantly graze Phaeocystis in
the field, we are developing an immunochemical method to detect
Phaeocystis within the krill digestive system.  Preliminary results using
this antibody assay on field-collected krill are presented.