TITLE:    Interannual and seasonal variability of the grazing impact of 
	  Euphausia superba in the Palmer Long-Term Ecological Research 
          region west of the Antarctic Peninsula

AUTHORS:  L.B. Quetin, R.M. Ross, K.L. Haberman, M.O. Amsler

MEETING:  Carbon Fluxes and Dynamic Processes in the Southern Ocean:
	  Present and Past

DATES:    28-31 August 1995

PLACE:    Brest, France


ABSTRACT: The Palmer Station Long-Term Ecological Research project (Palmer 
LTER) focuses on the pelagic marine ecosystem and the ecological processes 
which link the extent of annual pack ice with the biological dynamics of
different trophic levels.  A general objective is to document interannual
variability in the bio/physical interactions within the pelagic marine
community west of the Antarctic Peninsula.  One important question to
address is the interaction between the grazers and the primary producers. 
Our focus in this paper is the interannual and seasonal variability in the
flow of carbon from the primary producers through the grazers in the Palmer
LTER study region.  We utilize results from three austral summer cruises
(January/February of 1993, 1994, and 1995) and one sequence of seasonal
cruises (summer, fall and winter 1993) to illustrate seasonal and
interannual variability in the distribution of the dominant
macrozooplankton grazers, Euphausia superba and Salpa thompsoni.  The
relative and absolute abundance of these two grazers varied by at least an
order of magnitude on the spatial and temporal scales observed.  During the
last 3 austral summers the abundance of Antarctic krill varied among years
by a factor of 10.  Only during the summer of 1994 were salps more than an
incidental part of the total catch.  However, in 1993 salps were abundant
in the northern part of the grid in the fall; in the southern part of the
grid Antarctic krill were the dominant grazer.  This variability in the
temporal and spatial distribution of these two grazers leads to variability
in grazing pressure on the same scales.
     Estimates of carbon flow through Antarctic krill are calculated by
integrating grazing parameters from laboratory experiments that show the
dependence of grazing rate on standing stock with estimates of standing
stock in the field (Vernet et al., Brest 1995).  We present temporal and
spatial variability in grazing rates, fecal pellet production and percent
of primary production ingested and egested by Antarctic krill.  Fecal
pellet production and sinking rates as a result of the estimated grazing
rates are derived from published estimates of assimilation efficiency and
fecal pellet sinking rates.  The impact of grazers on primary production is
calculated by comparing our derived grazing rates with primary productivity
estimates on the same space and time scales (Smith, et al., Brest 1995).