2018 seçim sonuçları Movement Capture & Real Numbers!

Limnol. Oceanogr., 26(6), 1981, 1062-1073
Copepod feeding currents: Food capture at
low Reynolds number1
M. A. R. Koehl
Department of Zoology, University of California, Berkeley 94720
J. Rudi Strickler
Australian Institute of Marine Science, Townsville, Queensland, Australia
Abstract
High-speed motion pictures of dye streams around feeding Calanoid copepods revealed
that these important planktonic herbivores do not strain algae out of the water as previously
described. Rather, a copepod flaps four pairs of feeding appendages to propel water past itself
and uses its second maxillae to actively capture parcels of that water containing food particles.
The feeding appendages of Eucalanus pile&us operate at Reynolds numbers of only 1O-2 to
10-l. In the viscous world of a feeding copepod, water flow is laminar, bristled appendages
behave as solid paddles rather then open rakes, particles can neither be scooped up nor left
behind because appendages have thick layers of water adhering to them, and water and
particle movement stops immediately when an animal stops beating its appendages.
Calanoid copepods are abundant
planktonic crustaceans that play a major
role in the transfer of energy through marine
food chains. Copepods are selective
feeders, exhibit a plasticity of feeding behavior
(e.g. Poulet 1974; Richman et al.
1977, 1980; Cowles 1979; Donaghay and
Small 1979; Runge 1980; Skiver 1980),
and can markedly influence the composition
of phytoplankton populations (e.g.
Porter 1973; Poulet 1973; McCauley and
Briand 1979). In spite of the ecological
importance of copepod feeding, the
mechanisms by which these animals capture
particles (such as diatoms and flagellates)
have been poorly understood
due to the technical difficulties involved
in observing feeding appendages only
fractions of a millimeter long that are
moving at rates of 20-80 Hz.
Until now, descriptions of copepod
feeding have been based on careful microscope
observations of currents produced
by copepods in drops of water (e.g.
Cannon 1928; Starch 1929; Marshall and
Orr 1955). The “textbook description”
l This work was supported by grants from the
Natural Sciences and Engineering Research Council
of Canada, the National Science Foundation
(OCE76-01142), and the University of California,
Berkeley (Committee on Research).
(e.g. Russell-Hunter 1979; Barnes 1980)
of copepod feeding based on such observations
is basically as follows: The beating
of the feeding appendages (labeled in
Fig. 1A) pushes water postero-laterally,
forming a large swirl on each side of the
animal (Fig. 1B). Some of this swirling
water is sucked antero-medially by the
outward swing of the maxillipeds. The
inward swing of the maxillipeds then
pushes water between the setae and setules
(bristles on the setae) of the second
maxillae, which sieve particles out of the
water. The filtered water is then expelled
anteriorly by the first maxillae, and the
captured food is transferred to the mouth
by the endites of the first maxillae. We
suspected that the recirculating swirls
were artifacts of the small volume of
water in which the observed copepods
were immersed. Furthermore, we were
puzzled by water flowing between the
closely spaced setae and setules of the
stationary second maxillae rather than
flowing around them along the paths of
least resistance.
Attempts to analyze the feeding behavior
of Calanoid copepods have been based
on the concept that they feed by sieving,
as described above. For example, several
analyses of size-selective feeding by copepods
have focused on the spacing of
the setules on the setae of the second

2018 seçim sonuçları Movement Capture & Real Numbers!
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