Journal of Plankton Research, Vol 21, 1939-1956, Copyright © 1999 by Oxford University Press
S Beaulieu, M Mullin, V Tang, S Pyne, A King and B Twining
Long time series and/or spatially extensive observations of zooplankton are
needed in order to examine fluctuations in community composition and
biomass. We tested the utility of a laboratory optical plankton counter
(OPC) in determining the size spectra and biomasses of a large number of
preserved zooplankton samples. OPC size measurements of a variety of taxa
from the California Current region were well correlated with visual
measurements (r2 = 0.80). Although organisms
preserved for long time periods may fragment, trends in total biovolumes of
800 samples that were >10 years old were consistent with
displacement volumes measured just weeks after collection. A laboratory
test in which euphausiids were damaged manually indicated that OPC counts
of large zooplankton are robust to moderate fragmentation. The greatest
effect of formalin preservation on crustacean zooplankton was increased
opacity, resulting in an increase of 3-25% over the digital sizes measured
when alive. Formalin preservation significantly reduced the biovolume of
gelatinous zooplankton measured when alive. Formalin preservation
significantly reduced the biovolume of gelatinous zooplankton measured
visually, but did not change the size measured by the OPC due to the
compensating increase in opacity. As examples of the advantage of using the
OPC to analyze a large number of preserved samples, we examined (i) the
positive relationship of biomass to chlorophyll a in
three size classes at >100 stations occupied during a 1984 cruise
and (ii) the longshore pattern of size-fractionated zooplankton biomass in
800 samples from the California Current region in 1981 and 1984.
ORIGINAL ARTICLES
Using an optical plankton counter to determine the size distributions of preserved zooplankton samples
Marine Biology Research Division, Scripps Institution of Oceanography, La Jolla, CA 92093-0202, USA; Marine Life Research Group, Scripps Institution of Oceanography, La Jolla, CA 92093-0218, USA; Present address: MS #9, Applied Ocean Physics and Engineering Department, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA; Present address: Marine Sciences Research Center, State University of New York, Stony Brook, NY 11794-5000, USA
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