Bulletin of Plankton Society of Japan Vol. 30, No. 2, pp. 147-158, 1983
Grazing of Various Developmental Stages of
Pseudodiaptomus marinus (Copepoda : Calanoida)
on Naturally Occurring Particlesl''
Shin-ich工Uye3)
and
Shogoro
Kasahara3)
Faculty of AJ押Iied Biological Science, Hiroshima University,
Fukuyama, Hiroshima, 720
Abstract
Comparative grazing experiments of various developmental stages and sexes of the inshore marine
copepod Pseudodiaptomus marinus on naturally occurring particles were carried out. The feeding
behavior was similar between both sexes of the adult, but digerent between developmental stages.
The adult females were capable of consuming almost all particles from 2.8 to 63.3 /*m diameter,
showing selectivity for larger particles (ca. 50pm) where the peak of particle concentration
occurred. The nauplii consumed mainly smaller particles (<30/im). The consumption by copepodites was intermediate between that of the nauplii and adult females, since they fed upon both
smaller and larger particles. Such intraspeci丘c di庁erences of grazing behavior may lead to the
effective utilization of heterogeneous natural food resources.
The ingestion rates of the adult females increased linearly with the increase of particle
concentrations, without indications of the threshold nor saturation response. The amount of
ingested carbon rarely met the requirement for potential egg production which was observed
for the wild population. Thus, it was surmised that the adult females could ingest su缶cient
food deposited on the sea-bottom during a daytime epibenthic phase to attain predicted egg
production.
Since the copepods are the major constituents of the herbivorous zooplankton, their feeding
behavior has been studied by numerous workers (MARSHALL 1973, CONOVER 1978a, for
review). Despite this, many questions still remain unanswered. One of the questions which
has not been fully answered is how feeding behavior differs between developmental stages and
sexes. Most studies have been conducted with adults, usually adult females. However, younger
stages are usually much more abundant than older stages in natural copepod populations.
Therefore, to estimate their grazing impact, it is necessary to know how grazing behavior
changes through development. The grazing of various developmental stages has been compared for laboratory-reared copepods (MULLIN & BROOKS 1967, 1970, HARRIS & PAFFENhofer 1976, Paffenhofer 1971, Paffenhofer & Harris 1976) fed with cultured phytoplankton. However, no work, to our knowledge, has been performed on the grazing of immature stages of copepods on naturally occurring particles, except for works by ALLAN et al.
(1977) and POULET (1977). The second question is how the feeding rate of copepods is
affected by the change in concentration of available food. Saturation-type feeding (i.e. ingestion rate is proportional to concentration of food up to a certain level, above which it becomes
3 Accepted 24 September 1983 at the authors'own charge for publication.
3 pseudodiaptomus marinus (橿脚亜綱:カラヌス目)の各発育段階での天然懸濁粒子の摂食
3)上 真-・笠原正五郎,広島大学生物生産学部
148
0#7°y
constant
1972,
or "saturated")
has been
FROST 1972).
on natural
and
posed
a linear
natural
Saturation
phytoplankton
(1978b)
VV h y¥å £&>%30%%2%
frequently
observed
of ingestion
assemblages
rate
model
to describe
the
in
laboratory
has also
(PARSONS
MAYZAUD & POULET (1978)
(1983)
been
et al.
have
1967).
criticized
relationship
the
between
studies
(CORNER
observed
for copepods
On
contrary,
the
saturation-type
feeding
rate
et al.
feeding
CONOVER
model,
and food
and
pro-
supply
under
conditions.
The
tions
present
investigation
by examining
the
naturally
occurring
has
grazing
been
of
conducted
the
inshore
marine
Since
our preliminary
(UYE
et al.
sites
data
1982,
ranged
to answer
copepod
above-mentioned
Pseudodiaptomus
ques-
marinus
on
particles.
Materials
from the fall
primarily
1983),
showed
the
population
peak
from 16.8
that
present
and
P. marinus
feeding
is most
experiments
of 1978-1982,
to 22.3°C.
Methods
abundant
when the surface
The
water
in early
were carried
samples
summer and fall
out by using
water temperature
were taken
specimens
at the sampling
at Tomo, Fukuyama,
with
a 6-1 Van Dorn water bottle
at a depth of ca. 5m. Zooplankton
were collected
by vertical
or oblique
tows with a 0.45m
net (330fim
mesh opening)
either
at Tomo or Fukuyama
Harbor,
the
nocturnal
night
distance
migrators,
(VALBONESI
of this
species.
in the
were then
Adult
dites
the
eggs
culture,
cod-end
the
top
of P. marinus
immediately
in these
samples
hundred
GF/C)
Pavlova
They
were
in
(NV
and VI)
were
their
positive
phototaxis,
lutheri,
grazing
that
they
After
after
7-9
(CIII-V)
days
seawater,
The
ca. 30min.
nauplii
a stock
beakers
Thalassiosira
containing
to hatch
filtered
sp. added
as food.
cycle).
by taking
were individually
from
containing
light
of culture
To begin
dishes
were permitted
12L-12D
samples
and copepo-
culture.
2-1 glass
1-1 glass
and
surface
mixed zooplankton
into
nauplii
catch
Zooplankton
screw-capped.
However,
room (20-22°C,
beakers
and copepodites
required
from
to
tertiolecta
temperature
from the
the
transferred
time.
containing
which
are
column at
a sufficient
local
being
were sorted
P. marinus
water
yielded
from the
were obtained
of
in the
before
experiments.
females
Dunaliella
a constant
sorted
laboratory,
were sorted
for
were
bottles
seawater
seawater.
they
adults
collections
2-1 plastic
to the
gravid
filtered
2 days,
nighttime
additional
and males
Since
homogeneously
made from 19 to 22hrs
into
with
transported
of
kept
only
was usually
the
ca. 10km.
rather
were then
(Whatman
with
being
were diluted
to
several
for a period
seawater
sampling
and used
were so rare
glass fiber
distributed
filled
females
pipettes
stock
sites
are
& HARADA 1980),
water and animals
with
these
they
Hence,
concentrated
which
between
i.e.
pipetted
Nauplii
advantage
after
14-17
of
days
of culture.
First,
we examined
and sexes
each
nauplii
glass
of P. marinus
grazing
experiment,
were picked
bottle
containing
out,
differences
in
in response
20 adult
rinsed
natural
with
the
to the
feeding
behavior
same size
females
and
filtered
seawater
seawater
filtered
of various
composition
males,
of the
40 copepodites
developmental
food
and
and each group was placed
through
a 102j«m
sieve
to
stages
particles.
For
several
hundred
into
a 500ml
remove
larger
UYE & KASAHARA: Grazing
particles.
Each
rotating
bottle
was wrapped
at 1-2rpm.
room (20-22°C).
experiments
the
end
At
of
with
analysis
of developmental
of the seawater before
Counter
(Model
B or ZB)
before
and after
size
the
the
seawater.
of several
these
small
aggregate
the
lumps
of the
formation
by
bottles
copepod
after
with
concentration
indicated
in grazing
for survival
with
formalin
The particle
size
with a Coulter
quantity
of particles
particle
concentration
degree
concentrations
glass fiber
oxygen-saturated
data
on egg production
rather
formation
filter
seawater
which
(Whatman
40-45
(UYE
using
seawater,
individuals
for 18-20h
et al.
that
The
to
26.0%
decrease
female,
of particle
concen-
to measure.
particulate
(Yanagimoto
through
organic
Co., Model
a 102/nm
sieve,
rate of adult
BOD bottles
growth
bottles
% of the initial
respiration
dark
The
due to
18.9
was impossible
adult
a CHN analyzer
at 20°C.
caused
in grazing
the
ll
bottles
several
from
agitation
(i.e.
in the
GF/C).
Since
formation
with concentrations
from 3.10 to
formation
was more pronounced
had been prefiltered
into
formation
concentration
ranged
bottles
in grazing
the
chambers.
lump
of particle
arbitrarily
energy
grazing
the
of more water
in control
of ingested
natural
by incubating
with
because
were measured
the
a precombusted
lump
allocation
decrease
no animals)
for the seawater
the aggregate
that
was one half
of the
of the
net,
of P. marinus
concentration
of
observed
in the
mesh
The
We assumed
bottles
with adult
females
rate and particle
we occasionally
a 102p.m
bottles,
activity.
filtering
was measured
with
rate.
the
(POC)
The
of the
wheel
controlled
were checked
diameter.
of 2-3mm diameter
by sieving
(containing
tration),
MT-3),
a temperature
were preserved
the difference
experiment,
bottles
in grazing
carbon
of this
ingestion
feeding
discussion
149
to a grazing
measurement.
was determined
of grazing
experiments
between their ingestion
copepod
than
since
in
animals
140ptva
from
attached
copepods
The
of
in control
concentration
For
and
15-24h
the
net.
orifice
of aggregates
(mean:
22.0%)
of the initial
4.47ppm.
Visual
observations
in control
mesh
an
course
were removed
overestimation
bag
particles
grazing.
During
lumps
experiments,
was calculated
Second, we conducted a series
in order to observe the relationship
the
vinyl
stages and body
length
and after
the experiment
using
group
a dark
marinus on natural
were run for
a 102[im
for later
distribution
consumed for each
with
The
and removed by sieving
of Pseudodiaptomus
rate
(ca.
females
100ml)
filled
was estimated
from
1982).
Results
Six
Grazing of Various Developmental
experiments
were carried
out to examine
grazing
tween nauplii,
females
(Figs.
(Experiments
1 and
periment,
periments.
bimodal
the
copepodites
larger
2).
but
III
The
larger
The
distribution.
particles
and adult
& IV)
and
particle
particles
smaller
females
size
(ca.
particles
Microscopic
and unidentified
between
(Experiments
adult
distribution
50[im
(ca.
of
I & II),
females
the
diameter)
5/um)
Stages and Sexes
differences
in the grazing
and
natural
were
revealed
flagellates
were
most
that
the
males
nauplii
differed
abundant
in
in Experiments
Ditylum
major
brightwellii
constituents
be-
and adult
(Experiments
seawater
were also abundant
observation
between
behavior
V & VI)
in each
ex-
most of the
ex-
II-IV,
showing
constituted
of the
smaller
B&7°7 y? h y^^#^30#^2^
150
(1983)
0.4
o^/-
10
?0"
50 "100
Particle
Fig.
Diameter
(-xi
m)
1. Comparative
feeding
between nauplii,
copepodites
and adult females
of
Pseudodiaptomus
marinus on natural particles.
Particle
size-biomass
distribution before and after
the grazing
is expressed
as filled and open circles,
respectively.
Hatched
area denotes consumption
by grazing.
UYE & KASAHARA:
Grazing
of Pseudodiaptomus
marinus
on natural
151
particles
0.3
E
D
~° 0.2
CL
.^o O^h
fd
~0.4|
c
Eu
0.3]
o
Si 0.2
o
* 0.1
OHh
5
10
20
"50"
Particle
Fig.
particles.
The
2.
total
diameter.
The
adult
indicating
and intermediate
peaks,
with
higher
particles
the
particles.
however,
ca. 50^m
exception
On the other
differed
of
Experiment
hand,
greatly
the
in
Experiment
II,
particles
larger
particles.
higher
where
they
consumed
by
adult
in Experiment
females
did
were abundantly
the
feeding
slight
grazed
of adult
was observed
this
the
peak
was especially
males
in the
consumption
the
The
than
peaks
of smaller
particles
between
few on the peak
of small
were predominantly
those
was not consumed, excepting
in
particles,
as were adult females.
particles
as did
the particles
in Experiment
with
with
II.
same as that
of particles
by the
grazed
that
apparent
was essentially
size and concen-
most abundantly
rates
of smaller
It was also observed
in
Fig.
of adult
12 and
nauplii,
while
biomass
peaks
2 shows that
females,
50p.m
while
diameter
a
in
VI.
We calculated
category
they
it well.
consumed;
behavior
difference
Experiment
II,
not graze
V to 3.297ppm
nauplii
smaller
than ca. 30p.va diameter,
the peak of larger
particles
Experiment
IV.
Copepodites
were able to consume larger
However,
experiments.
from 2.8 to 63.3pm
on particle
grazed
slightly
the
all particles
always
for
at
100
throughout
depending
were
grazed
50
females
and males of PseudoSymbols
as in Fig. 1.
2.263ppm
selectivity
also
20
to consume almost
diameter
feeding
were
10
was abundant
from
were able
consumption,
of
matter
varied
females
particles
females,
particulate
concentration
Adult
Their
tration.
organic
particle
VI.
-5
Urn)
Comparative
feeding
between adult
diaptomus
marinus on natural particles.
Nonliving
Experiment
"100"
Diameter
in terms
the
feeding
of percentage
efficiency,
of the
i.e.
initial
the
particle
rate
of
consumption
concentration
(Fig.
of each
3).
particle
In this
case,
size
the
R^L-fy Vt Y y^^m.^^%^2^
152
feeding
efficiency
stages,
the
certain
size categories.
copepodites,
higher
of the negative
efficiency
but
The
rate
on smaller
efficiencies
consumption
was not homogenous
often
was assumed
spectra,
indicating
higher
on larger
particles
was always
with
particles
the
to be zero.
over the
and intermediate
coincided
(1983)
biomass
for nauplii.
peaks,
but
[Adult
For all developmental
selective
for adult
Fig.
this
feeding
females
3 also
indicates
was not evident
20
50
100
Particle
Fig.
Diameter
females
10
(jum)
20
50
100
3. Comparison
of the feeding
efficiency
of nauplii,
copepodites
adult
females
of Pseudodiaptomus
marinus.
Triangles
denote
position
of peaks of particle
concentration.
and
the
6Or
/
= 6 . 2 6 + 7 . 2 0
( r =
P
0 .7 2 2 )
A0|-
I
o 201・
・
I
・
2
Particle
Fig.
4. Ingestion
rates of an adult
at various particle
concentrations
Ingestion
A total
of 38
ranging
from
where
the total
Rates
grazing
0.66
of Adult
experiments
to 5.02 ppm.
particle
concentrations
Females
were
The
3
A
Concentration
aggregated
by volume)
female of Pseudodiaptomus
marinus
expressed as volume. (See text)
at
Various
performed
were higher
(P:ppm
Particle
in seawater
lump formation
than
2.38
ppm.
Concentrations
with
particle
was observed
In these
concentrations
on 15 occasions,
cases,
and
that
for nauplii.
La*
10
on
the
ingestion
UYE & KASAHARA:
rates
were expressed
in controlls,
the
it is close
d"1)
become
upper
of Pseudodiaptomus
bars
the
(Fig.
lower
concentration
variance
was used
was a linear
of the variance
4).
results
within
the
in ppm)
as the
Ingestion
The
neither
of particle
relationship
carbon
that
Rates
between
concentration
for
this
from the
particle
be expressed
1.07
present
in Relation
volume
in /ugC •EI"1)
from
of the
d"1.
growth
regression
models.
(/, in 106/<m3«
Minimization
of the
The
best
fit
to
basis
the
to carbon
took
concentration
giving
place
for
P. marinus
(P,
and Growth
in ppm)
and particulate
for 34 seawater
the
following
Rates
samples
equation
(Fig.
organic
with
volume
5):
(r=0.923).
data
basis
from
the
grazing
(Fig.
6).
The
experiments
ingestion
were converted
rate
(Ic,
in figC)
can
as:
Assuming
in mature
of the
as
is few,
study.
was determined
to 7.70 ppm,
equation,
volume
respiration
rate
rate
4.
to Respiration
Ic= -0.12+0.0072
The
formation
ingestion
nor cessation
POC=101.8+97.8P
By using
is as abundant
in Fig.
fitness
saturation
Females
particle
(POC,
ranging
between
153
(r=0.722).
feeding
concentration
of Adult
concentration
formation
when aggregate
is shown
criterion
particles
model
rather
than a rectilinear
or curvilinear
model,
although
the
was minor between these models,
given by the following
equation:
indicated
range
but
The relationship
(P,
on natural
aggregate
bar,
7=6.26+7.20P
These
marinus
When
end of the
end of the bar.
and particle
sum of square
the data
difference
as vertical
rate
to the
animal"1
Grazing
rate
the
respiration
was estimated
females.
of an adult
The
female
quotient
from
specific
the
daily
of P. marinus
(RQ)
egg
POC.
is 0.8,
an animal
production
egg
was calculated
since
production
as 2.83 /ilO2«animal"1
respired
somatic
1.21,«gC
growth
rate
at 20°C
6
(P:ppm
by
would
was 0.183
1 000r
POC=101.8*97.8P
(r= 0.923)
j800|
^ 600h
J
<J>
o
EP 400
<-> 200
0'
Fig.
5. Relationship
particle
volume
2
Particle
4
Concentration
between particulate
concentration.
organic
carbon
8
volume)
concentration
and
•Ed"1.
The
be negligible
(UyE
et al.
0#7°7>?
154
h >^£»30#|jl2^-
(1983)
6r
Ic
E 5h
=
- 0 .1 2
( r =
+
0 .0 0 7 2
P O
C
0 .7 2 2 )
? Af-
・
(2 )
・・
°
・
- ** ・
・
2h
・
(1 )
・
・ ・
・
c
*
・
^^
Fig.
1982),
which,
B^ ^ " "^ ^ " !^
30 0
P O C Concentration
200
4
i^
00
500
(POCrju.gr1)
600
6. Ingestion rates of a n adult female of P s e u d o d i a p t o m u s m a r i n u s a t
various particle concentrations expressed as c a r b o n . Lines denote the
estimated food r e q u i r e m e n t s for metabolism (1), and for metabolism
plus predicted
egg production (2).
multiplied
by
the
average
body
carbon weight
of an animal (4.89j«gC),
gives
the daily egg production rate:
0.89/*gC •Eanimal""1 d"1. The ingestion rates which would be
needed for metabolism, and metabolism plus predicted
egg production w e r e calculated using an
assimilation
efficiency of 0.7 as 1.73 and 3.00//gC •Eanimal"1, respectively.
These t o w v a l u e s
are indicated
by horizontal
lines in Fig. 6. The ingestion rates w e r e usually higher than the
requirement
did
for metabolism,
not meet that
egg production
animal ingested
but in 9 experiments
requirement.
The ingestion
w e r e observed in ll
experiments
m o r e than for metabolism,
at lower concentrations,
rates
the ingestion
m o r e than estimated
at higher
but less than
concentrations.
for potential
rates
to be necessary
for
In most cases, the
egg production.
Discussion
Grazing of Various Developmental Stages a n d S e x e s
There w a s n o discernible
difference
P . m a r i n u s , while the difference
In studies
females
using
laboratory
of copepods
Richman & Rogers
attributed
to a better
filter
1969,
in
cultures
larger
behavior
at higher
Paffenhofer
efficiency
1971,
for
between adult
between developmental
of algae,
cells
retention
N l V A L 1976, FROST 1977).
(POULET 1973, 1974), adult
grazing
w a s apparent
m a n y investigators
Frost
1972,
particles
1977).
and males of
(Figs.
have reported
rates than the smaller
larger
females
stages
cells
This
by filtering
1 & 2).
that adult
(MULLIN 1963,
fact is commonly
setae (NlVAL &
However, in studies using natural particle assemblages of seawater
females of Pseudocalanus minutus w e r e able to c o n s u m e p a r t i c l e s
between 4 and 100//m diameter,
eaten than the larger particles.
but on the average intermediate particles
were more readily
They opportunistically
shifted
their
grazing pressure from
o n e size range to another depending
on where the particle
peak occurred.
R l C H M A Net al.
Uye & KASAHARA: Grazing of Pseudodiaptomus
{1977)
also
investigated
A. clausi
the
on natural
capabilities
for
as well
as biomass
suggested
that
grazing
grazing
of
over a broad
peaks.
the
The
copepods
always
The
the
particle
showed
higher
shift
of grazing
Since
copepodites
that
for them
than
as those
Acartia
strated
for
of
of copepodites
smaller
copepodites
than
adult
copepodites
minutus
diameter).
species
with
they
feeding
et al.
observed
in the
MULLIN
& BROOKS (1967)
Calanus
adults.
experiments
natural
particles,
change
marinus
of feeding
for
nauplii
i.e.
of different
(1977),
but
appeared
range
to
the
grazed
most by them.
pacificus,
The
at
to handle
Selective
using
its nauplii
not
feeding
cultured
adults
(Fig.
mainly
of
suggested
on particles
3) is also
on larger
for
smaller
common for
could
not
categories
the
Eurytemora
any
grazing
by the
consume larger
diatoms
the
was also reported
plastic
nauplii
on certain
peaks
nauplii
size
on
to
was rejected
rates
by
of P.
categories
were not always
by FERNANDEZ (1979b)
pollen
spp.
capability
since
biomass
beads,
fed
nauplius
in comparative
in their
investigation
higher
However,
from
affinis and Acartia
difference
by copepod
present
(Figs.
same difference
On the contrary,
of
phytoplankton,
the most striking
size
observed
observe
selective
3).
consisting
occur by metamorphosis
disproportionately
(Fig.
the
as demonthe grazing
was also
of P. marinus,
is convincing.
was supported
consume
capable
and adults
copepodites
sizes.
this
particles,
study
adults
as
POULET 1977).
changes
did
the
more
appendages
examined
particles
than
present
of grazing
behavior
and
of fine
than
is
were
feeding
(1977)
FERNANDEZ (1979a)
morphological
ALLAN et al. (1977)
within
of Calanus
and
they
behavior
particles
the
mesh size
occurring
was incapability
pacificus,
As great
consume particles
ALLAN et al.
nauplii
1977,
to
since
grazing
intermediate
more food
of copepodites
switched
peak also occurred.
their
POULET
in the
feeding
1 & 3).
laboratory-reared
obtained
(ALLAN
the
particles,
smaller
importance
observed
successively
of P. marinus
may possess
on naturally
The
particles
distributions
ones was not obvious.
and
but
of other
feeding
smaller
have
and
similar
on larger
where the biomass
Copepodites
they
selection
on multiple-peak
females
to smaller
adults,
since
adult
consume larger
However,
tonsa
demonstrated
and then
particles,
particles
by NlVAL & NlVAL (1976).
species
the
for
clausi
selective
to copepodite,
particles
155
affinis, Acartia
species
with
particles
phenomenon can not be explained
solely
by
of the feeding
appendages.
In the present
of the
The
upon by the
size,
adults.
difference
of
larger
This
sieve
could
three
experiment
for the
of this
In comparison
particle
for large-sized
females.
(<22/zm
10p-xa.
on
from larger
of Pseudocalanus
particles
fed
of P. marinus
important
of
of the grazing
categories.
by a fixed
selectivity
of Eurytemora
These
was most important
pressure
more like
functional
range
first
size
females
particles.
results
biomass peaks of smaller
size
the simple
mechanical
filtering
experiment,
of adult
distributions
marinus on natural
grains
for nauplii
and detritus
as
food.
In natural
tration
change
biomass
the
conditions
the
particle
distribution
is
change in space and time.
In such a dynamic
of particle
distribution.
Obviously,
the selective
peaks
dominance
may convey advantage
of certain
size
categories
in
maximizing
(POULET
heterogeneous,
energy
1973,
i.e.
system,
copepods
grazing
on larger
1974).
intake
Since
the
size
and lead
the
and
concen-
may adapt to the
particles
as well as
copepod
to minimizing
community
156
0#7°y
consists
of various
competition
species
for the
of five
copepod
Acartia
clausi
species
reported
the
that
Calanus
and the
data
nauplii,
copepodites
size
competition
revealed
that feeding
the natural
In the
Ingestion
Rates of Adult Females
experiment,
the seawater
for
taken
at Tomo.
dictory
from the
same
ingestion
rates
indication
when fed with
inconsistency
linear
particle
location.
data
that
P. marinus
Thalassiosira
to the
However,
digestive
system
from
minutus
study
and
(Figs.
are separated
1-3)
between
can be utilized
change
effectively
showed
of
five
natural
of time
for
food
4).
copepod
without
was contra-
saturation-type
species
They
Harbor
environment
This
antiqua.
were
functional
The reason for this
They
found
and naturally
criticized
the
a
occurring
saturation-type
an artifact
resulting
from too sudden exposure
source.
The planktonic
copepods
were capable
food
(18-20h)
(MAYZAUD & POULET 1978).
by REEVE & WALTER (1977)
Fukuyama
concentration
(Fig.
a typical
investigations.
of heterogeneous
period
particle
response
grazers
and MAYZAUD& POULET (1978).
rate
a year-course
a short
from
of natural
sp. and Chattonella
suggesting
that it was perhaps
the amount of a single
food
adapting
change
on the
nor saturation
ingestion
from
activity.
present
niches
P. marinus
to the
dependent
threshold
cultured
between
concentration
of feeding,
increasing
in the
food resources
However,
was given by CONOVER (1978b)
relationship
partitioning,
Pseudocalanus
at Various Particle
Concentrations
food suspension
and experimental
from Tomo and
were totally
of the
to our unpublished
response
pressure
HARRIS (1982)
competition.
to P. marinus
Its
any apparent
grazing
in resource
evidence
Therefore,
their
was important
behavior
the
herdmani,
similarly
competition.
grazing
provide
females
reacted
by shifting
The
adult
copepods
interspecific
of small-sized
and adults.
similarly
spectrum
and interspecific
Eurytemora
these
behavior
intraspecific
behaved
All
grazing
pacificus.
intraco-existing
Temora longicornis,
severe
by reducing
not always
consider
compared
of the
of POULET (1977)
present
we should
particles.
indicating
interspecific
examination
minutus,
of particle
another,
(1983)
POULET (1978)
on natural
change
to
the
comparative
large-sized
similis)
to the
stages,
resources.
{Pseudocalanus
and Oithona
from one size range
also
and developmental
same food
and simultaneously
yV \ y^^MM>30#02^
Acartia
by regulating
was
their
not enough
Similarly,
digestive
for
nonsaturated
enzyme
acclimation
feeding
tonsa and by HUNTLEY (1981)
for
to
of
of
the
was reported
three
species
of
the genus Calanus
on natural
particles
covering
the whole range of the annual fluctuation.
The particle
concentration
used in the present study did not cover the whole range encountered
in nature
occurs
by P. marinus.
in
nature.
meaningless
at
ppm (=166
The
rarely
the
exceeded
ingested
suggest
least
that
our previous
the
within
and 593//gC
present
We therefore
However,
the
was not
growth
findings
conclude
that
a critical
of the
demonstrated
the requirement
the
range
not
of
the
concentration
particle
saturated
feeding
may be
concentration
between
0.66
never
ecologically
and 5.02
•EI"1).
experiment
carbon
can
concept
rate
did
not
that
for predicted
enough
even
the
egg
for
amount
production
metabolic
of P. marinus
is dependent
support
We found
this.
of carbon
(Fig.
6).
requirement
on food supply
that
in situ
egg
ingested
by P. marinus
On several
(Fig.
6).
in nature.
production
occasions,
These
data
However,
rates
were
UYE & KASAHARA: Grazing of Pseudodiaptomus
temperature-dependent
field
populations
(UYE et al.
equal
bably,
rather
than
1982).
numbers
phase
We gratefully
thanks
There
is
pellets
the
since
populations
no diel
both
can ingest
to attain
fed
feeding
in
plentiful
food
potential
the
with
periodicity
daytime
for
deposited
assistance
57108017.
We would like
to
dedicate
were
on
always
higher
phytoplankton
P. marinus,
the
157
for
ad libitum
since
they
egested
(darkened).
sea-bottom
during
Proa daytime
egg production.
in the
of Education,
this
particles
and nighttime
critical
are also due to Dr. T. ONBE for comments during
from the Ministry
rates
cultured
(illuminated)
Acknowledgements
Dr. M. HUNTLEY for
acknowledge
to Mr. T. KURIHARA for
by grants
food-dependent,
for laboratory
of fecal
P. marinus
epibenthic
than
marinus on natural
feeding
Science
paper
reading
of the
preparation
experiments.
and Culture,
manuscript.
of the
This
Project
Our
manuscript
and
work was supported
No. 511917,
to Dr. R. MARUMOin celebration
56115019,
of his
sixtieth
birthday.
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