TITLE:    Palmer LTER: Grazing by the Antarctic krill, Euphausia superba, on
          Nitschia sp. and Phaeocystis sp. monocultures
AUTHOR:   Karen L Haberman, Robin M Ross, Langdon B Quetin
Palmer LTER Contribution #18
ANJ 1993  V28(5) pg 217-219

Previous studies suggest that growth and reproduction of Antarctic krill are
generally food limited in the Southern Ocean (Ross and Quetin, 1986).  While
Antarctic krill are primarily herbivores, it is not known whether they ingest
and assimilate different types of phytoplankton with similar rates and
efficiencies.  Such knowledge is important if we wish to understand how the
patterns of phytoplankton abundance and species composition affect the krill's
food availability.  In particular, can food availability be accurately
determined from measurements of total chlorophyll, or do we need to use more
detailed measurements of species composition?  The prymnesiophyte Phaeocystis
spp. is a relevant example.  While it periodically occurs in thick blooms and
can dominate the Southern Ocean phytoplankton assemblage at certain places and
times (Prezelin et. al., 1992), the question of its edibility and nutritional
value for various grazers has been the subject of several investigations
(Estep et. al, 1990; Hansen, Tande and Berggreen, 1990; Verity and Smayda,
1989; many others).  Results vary widely between these studies, and none have
been published on euphausiids.  Here we report the results of preliminary
experiments comparing the ingestion rates of krill on diatoms to those on
Phaeocystis sp. in laboratory feeding experiments.