Download Foragin Behavior of the Leather Seastar, Dermasterias imbricata

FORAGING BEHAVIOR OF THE LEATHER SEASTAR,
DERMASTERIAS IMERICATA (GRUBE),
IN MONTEREY BAY, CALIFORNIA
A Thesis Presented to
the Faculty of the Department of Biology
San Jose State University
In Partial Satisfaction
of the Requirements for the Degree of
MASTERS
OF
ARTS
by
Cynthia Ann Annett
August 1982
ABSTRACT.-Foraging behavior and prey choice of
masterias
imbricata,
from 1979 to 1981.
revealed
a
which
leather
sea
star,
De~-
investigated in the Monterey Bay area, California
were
stomach content analysis of
diet
the
consisted
mainly
of
290
free-ranging leather stars
the
corallimorphian anemone,
Corynactis californica. A survey of potential prey at the Monterey Coast Guard
Breakwater
showed
that
californica is the only locally abundant anemone
C•
which occurs in the same depth range as
was
found
in
presented
found within the
with a choice between
c.
californica
regardless
of previous diet.
study
site.
However,
cali£ornica and Anthopleura elegan­
tissima in the lab, 23 leather stars initiated
first,
corynactis
2
2
85% of 52 randomly placed 1/4 m quadrats and 96% of 45 1/4 m
quadrats placed around D. imbricata
when
£. imbricata.
feeding
on
A.
elegantissima
Leather stars also initiated feeding on
Anthopleura xanthogrammica first when given a choice between
~.
and
elegantiss~a,
C.
californica.
In
single
prey
presentations,
A.
xanthogrammica
xanthogrammica, and Metridium senile were all taken readily within
the
~.
first
day; in contrast leather stars presented with C. californica initially avoided
this species and 40% did not feed within 3 days.
individual
prey
behavior~
The effects of
species
and
differences, nematocyst sizes, and prey abundance
on leather star foraging behavior are discussed.
3
LIST OF TABLES
TABLE
1. Summary of prey reported in the diets
of D. imbricata in the field
2. Description of ~. eleqantissima­
£. californica experiments
3.
Number of C. caJ.ifornica found under
everted stomachs of feeding Q. imbricata
~ imbricata intiating feeding
on each prey species
7
16
22
4. Number of
26
5. Previous diet and subsequent prey choice of
~. imbricata when presented with £. californica
and !. eleqantiss~ simultaneously
28
6.
Number of anemones consumed in the laboratory
during three sets of three day observation
periods
7. Number of
~. imbricata initiating feeding on
anemones when presented with !. xanthoqrammica
and f. californica simultaneously
8. Summary of anemone behavior observed during
contact with D. imbricata in the lab
30
32
36
4
LIST OF FIGURES
FIGURE
1. Map of the Monterey
study areas
Peninsu~a
and
2. Identification photograph of D.
10
~ricata
3. Laboratory Set up
4.Prey taken by Q.
13
15
:in the fieJ.d
20
5. Percent cover of C. californica at the
breakwater
25
6. Time to initiation of feeding for Q.
33
~ricata
~ricata
presented with single prey species
of D.
irritation
7. Reaction
~ricata
to mechanical
40
5
ACKNOWLEDGMENTS
I
am grateful to the many persons who contributed their help to the
cessful
completion
of
this
University of California Long
space,
without
which
this
project.
Marine
project
Dr. John Pearse and the staff of the
Laboratory
provided
extensive
and
field work.
lab
the
throughout
Moss
Landing
aquaria
my
committee
Shilo
Drs.
and
I give my
Etter,
Barbara
Marine Lab divers who painfully endured the
Dr. Raymond Pierotti provided comments, discussions, text editing,
assistance,
research.
on
discussion and help in editing the manuscript.
heart-felt thanks to my diving buddies, Ken Nicholson,
Pierson,
valuable
could not have been accomplished.
James Nybakken, John Pearse, and Michael Foster served
provided
SllC­
and
emotional support which were invaluable
I would like to thank my parents
my studies.
for
thro~ghout
encouragement "and
My thanks to Lyn McMasters who prepared the
tiona in this manuscript. Finally Dr.
Ann
Hurley,
whose
this
guidance
i~lustra­
encouragement
and
advice helped me to begin this project.
This investigation was partially funded by a grant
Lucille Packard Foundation.
from
the
David
and
6
INTRODUCTION
The biology of the leather
Asteroidea,
order
star,
Spinulosida),
has
Dermasterias
imbricata
mode.
emphasize
three
main
1857 i
not been extensively studied.
researchers have reported dietary information for D. imbricata.
reports
(Grube
Several
All of
these
characteristics of the leather star's feeding
First, leather stars are capable of
feeding
on
a
variety
of
prey.
Mauzey et al(1968) report a diet consisting of at least 15 spp. in three phyla
and Rosenthal and Chess(1972) list at
Second,
despite
thi.s
varied
13
prey
spp.
in
five
phyla.
diet, most leathar stars in any given area are
found to be feeding on only one or
leather
least
two
prey
species
(Table
1).
Pinally,
stars feed a1most exclusively on sedentary or sessile prey, mainly in
the phyla Cnidaria and Echinodermata, especially those
wh~ch
occur
in
high
densities.
From this information, it is unclear whether D.
preference in the type of prey taken.
imbricata
exhibits
any
In any given area, leather stars may be
characterized as local specialists (Fox and Morrow
198~).
In
fact,
leather
stars may be specializing more on a limited number of prey types (e.g. sessile
or sedentary, dense, aggregating, etc.) rather than a limited number
species.
prey
However, even amongst closely related prey species there may be sub­
tle di£ferences in behavior
included
of
in
which
determine
whether
the
species
will
be
or excluded from the diet of the predator (see Moitoza and Phil­
lips 1979 for a pertinent example).
My study of the predatory behavior
parts.
of
D.
imbricata
consisted
of
two
First, I conducted an investigation of the diet of the leather star in
an area not previously investigated (central California). Second, a series
investigations
into
the
feeding
of
behavior of D. imbricata in the laboratory
Table 1:
Summary of pre:' renorted in the diet of
D. imbricata in the field.
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CD
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(1)
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CO
t-j ct>
~c"t
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M­
0
rt
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J-I
::s
It
I-'
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.......,
f\)
'--'
0
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........,
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.....
0.
•• :s
I-'
f\)
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J-I
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::1
:s
'l
rt
'--'
c.o
0..
C
o.:s
'--'
II
t-j
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:s
J--ooJ
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c:
CD 0
W
Q')
Ul
(l)
to
'-J
Q..
~~
J--ooJUl
p.l 0
:s
:sIt
to
..... OQ
J-I
•• P>
......
tde:
'-JC12
'..:I .....
.....
0')
~~
II
:s
OQ
.
It:j
.....
0
C1
'1
0
Leucilla nuttingi
3
0
unidentified
sponge
}-Ie
0
P'
Abietinaria spp.
0
nP'
+
+
0
+
0
0
0
Ptilosarcus gurneyi
Eoiactis orolifera
•
A. ele gantissima
A. xanthogramrnica
0
tolj
0
M. senile
0
::0
t'1j
to<
Tealia sp.
0
0
0
Tealia coriacea
en
t-tJ
t:J:j
Q
H
t:tj
Q
0
Tonicella lineata
0
Mopalia sp_
Q
Balanus carioslls
+
Cue umaria lubrica
0
Psolus sp.
+
0
Astrornetis sertulifera
•
s.
0
'~
0
•
0
purpuratus
unidentified urochodat
detritus
en
8
were conducted. The lab studies focused on the interaction between
cata
and
various
species
were examined in detail:
of anemone prey.
various species of prey.
2)
imbri­
Two aspects of this interaction
1) The effect of recent experience of
on subsequent prey choice, and
D.
the
predator
the behavioral responses of the predator and
9
METHODS AND MATERIALS
study Site Description
Observations on predator-prey interactions, distributions of D. imbricata
and
their
prey,
and stomach contents of D. imbricata were made at two major
sites, the Monterey Coast Guard Breakwater (1210 53'N, 360 36' W) and Stillwa­
ter
Cove in Carmel (121° 57'N, 36° 34' W).
Incidental observations were made
in several additional areas, including Cannery Row in
Monterey,
the
Hopkins
Marine Life Refuge in Pacific Grove, and the Carmel River Beach (Figure 1).
Twenty hours of underwater observations were conducted using
at
gear
the Monterey Coast Guard Breakwater (henceforth referred to as "the break­
water") between September and December 1981.
half
way
The main study area was
located
along the breakwater on the seaward side (Figure 1) and was identi­
fied on the surface from landmarks on the breakwater itself.
was
SCUBA
The
study
area
a loosely defined 50 meter area extending from the surface to the base of
the rocks at about 10 meters depth where the boulders and cobbles ended
in
a
sand plain.
Fifteen hours of underwater observations
Cove
between April and July
of
the
cliffs
in
Stillwater­
Dermasterias imbricata were found in three
(2
to
~).
the
10
Each of these areas were characterized by either
meters
in
height)
or large boulders, and were
strictly subtidal. Dermasterias imbricata were relatively rare in other
of the cove.
in
cove, and 3) at the base of a washrock located at the seaward
edge of the cove (Figure
vertical
conducted
1) Arrowhead Point, 2) on a large table mount
areas within the cove:
center
~980.
were
areas
Figure 1:
Map of the Monterey Peninsula showing
the location of the study areas.
II
stomach Contents Survey
In order to determine the prey species consumed by
Q.
imbricata
in
the
area
the
stomach contents of leather stars found in my study areas
were examined.
~l
D. Imbricata found during an extensive search of the study
Monterey
areas
were
checked
for prey.
If the leather star's stomach was
was usually the case) the stomach and substratum directly
below
checked for the presence of partially digested prey.
were
eve~ed
the
(as
stomach
If the stomach was
not everted, I forced the stomach and any prey out through the mouth by gently
pressing
on
the
aboral
surface near the anus.
found, as well as the size
and
location
of
the
The identity of any prey so
leather
star,
were
then
recorded on a plastic slate.
Prey Distribution
The percent cover of subtidal anemones was estimated at the breakwater in
order
to
stars.
determine
the
type and abundance of prey available to the leather
The percent cover of anemones occurring in 1/4 square
quadrats
was visually estimated and recorded on plastic slates.
were placed in one of two ways, either randomly or around D.
locations
of
random~y
random
distance
along
a
horizont~
vertica~
study area. Quadrats placed around
leather
~uminum
The quadrats
imbricata.
The
placed quadrats were determined by placing them at ran­
domly chosen distances along a
a
meter
star was in the center.
D.
meter tape which had been placed
at
meter tape located at the center of the
imbricata
were
placed
Quadrats were placed around
found within the study area during one day of diving.
~l
so
that
the
D. imbricata
Individual
}~rking
and
J.2
~easurement
Organisms were brought into the laboratory
for
more
detailed
observa­
A total of 46 Q. imbricata (Appendix I) were collected from the break­
tions.
water and kept in aquaria at the
University
of
California
Joseph
the aboral surface from the center of the disc to the end of each
was
then
photographed
and
(1972)
leather star.
length
of
Each
was
modified
from
Rosenthal
and
of attaching small colored plastic beads to the
A heavy duty embroidery needle
was
used
to
a
insert
short
12 lb. test monofilament fishing line under the epidermis near the
madreporite.
ously
consisted
arm.
(Figure 2) and tagged for identification.
The method used for tagging leather stars
Chess
Long
The leather stars were measured with a flexible meter tape along
Laboratory.
individual
M.
The
colored
fishi~g
small
line was then tied in a loop near the base and vari­
plastic
craft
beads were held in place by a second
beads were strung on the two ends.
kno.~
tied in the end
of
the
line.
The
In
this way, the leather stars were individually identified by their unique color
combination (see Figure 2 for an example).
the
leather
stars in any way.
I
These tags did not appear to
never found any wounds around the tags, any
obvious changes in the leather stars' behavior, or any behavioral
between
tagged
leather
harm
differences
stars and the five individually recognizable leather
stars used as controls.
Anemone prey were collected at several
with
Corynactis
californica
locations.
Small
rocks
covered
were collected at the breakwater (Appendix II).
Anthopleura elegantissima were collected from the Moss Landing Harbor, Terrace
Point
( Santa
Cruz) ,
and Davenport Landing (Santa Cruz County).
xanthogrammica were collected off mussels gathered
Cruz County).
at
Panther
Anthopleura
Beach
(santa
Metridium senile were obtained from a holding tank and had been
kept in the lab for an unknown period of time.
The oral disc diameters of all anemones except
ured.
Because
were measured.
of
the large number
£.
The oral disc diameters
f. californica were
meas­
californica used, only 40 individuals
(exclusive
of
tentacles)
of
fUlly
expanded anemones were measured underwater with a small plastic ruler.
elegantissima, A. xanthogrammica, and
by
a
number
floor.
~l
written
a
with
~.
senile were
individually
All A.
identified
grease pencil near their bases on the aquaria
c. californica on each rock were counted at the beginning and end
of each experiment.
Individual rocks were identified by numbered plastic tags
attached by a short length of monofilament.
The wet weight for six
six
groups
biomasses.
~.
elegantissima (1.0 em oral disc
diameter)
and
of five C. californica were measured as an indication of relative
Anemones were carefully removed from rocks and
scraped
clean
of
all adhering debris, then blotted dry before weighing.
Laboratory Observations
To
determine
behavior,
D.
the
effects
imbricata
were
of
recent
dietary
experience
on
feeding
kept in the lab for two weeks and then divided
into three groups maintained on restricted diets before experiments were
ducted.
Indiv~dua~s
was placed in a
tained
were
c~rcular
random~y ~~ocated
tank (1.5 meter diameter by 60 em
on a diet of chopped bait squid.
depth)
One group
and
This
group
of
leather
stars
referred to as "squid tank") were kept away from all anemones for
six weeks. The other two groups, consisting of seven leather stars each,
put
main­
Approximately 500 grams of squid was
placed in the bottom of the tank every week.
(henceforth
into the treatments.
con­
were
in each half of another circular tank which had been divided with a plas­
tic screen (Figure 3a).
The leather stars in one half of this tank were main­
Figure 3: Laboratory set up. A. Anthopleura and
Corynactis tank.
Note the plastic screen
in the center which acted as a divider.
B. Water table containinq C. californica
and A. eleqantissima. c.~ Divided water
table used for con~rolled prey presentations.
15
tained
on
tank n
while the leather stars in
),
a
elegantissima
diet
of
C. californica (henceforth referred to as "corynactis
(henceforth
the
referred
other
to
as
half
were
maintained
"Anthopleura
tank").
on
A.
Both the
anemone and squid tank were provided with flowing coarsely filtered sea
water
c.
at 15°
After being kept in the circular tanks on restricted diets for six weeks,
24
imbricata were used in a series of experiments on prey choice.
D.
these leather stars had been collected at the same time
same
manner.
and
treated
All of
in
the
Dermasterias imbricata used in later experiments were collected
at different times and maintained on sqUid diets for one to two weeks prior to
to experimental observations (Appendices I and III).
Prey choice experiments were conducted in a water table (2m x
~
x 20
em
deep) equipped with running sea water and a constant light cycle (12 hrs light
12 hrs dark; Figure 3b).
A.
elegantissima
as
Three replicates were run using C.
prey (Table 2).
In each
exper~ent,
californica
and
leather stars were
chosen from the circular tanks by assigning a random number to each individual
and
allocating
table.
them
according to the listing obtained from a random numbers
A similar technique was
used
to
allocate
individuals
to
rando~y
chosen parts of the water table at the beginning of each experiment.
Observations were made continuously for
experiment
and
first
two
hours
of
each
then for at least one hour a day until the termination of the
experiment.
Since the leather stars usually
feeding
inactivity
or
the
after
the
settled
into
long
periods
of
first two hours, constant observation was
deemed unnecessary, and instead the position and actiVity of all leather stars
and
prey were recorded at one to twelve hour intervals throughout the experi­
ments.
In total 25 hours of continuous observation
and
28
periodic
checks
Table 2: Description of ~.elegantissima/f. californica
choice experiments
Experiment #
2a
21:>
10/25/81-10/30/81
10/31/81-11/3/81
1
date
10/14/81-10/16/81
number
of leather stars
diet)
diet)
15 (12 from #2a
3 from squid tank)
X radius
9.52 em
(sd=1.S4cm)
9.22 em
(sd=1.26cm)
(sd=1.13cm)
number of
A. elegantissima
21
39
26
X
oral disc
diameter
1.9 em (sd=1.14 em)
2.1 (sd=O.78 em)
3.0 em (sd=O.71 em)
number of
californica
863 on 12 rocks
586 on 10 rocks
696 on 12 rocks
X oral disc
0.55 em (sd=O.22)
0.55(sd=O.22 em)
0.55 (sd=O.22 em)
9 (3
from
each
12 (4
from
each
9.23 em
c.
1.7
were made during the I I days of these experiments.
Further experiments on predator-prey interactions were conducted on
Q. imbricata presented with a variety of anemone prey.
lated
vations the water table was
f~erglass
inserting
screen (Figure 3C).
allowed
to
divided
p~itions
or
interact
Small M. senile (X-l.8 em
sd=1.15
em)
dividing
30
cm
2
elegantissima,
either~.
either
sd~O.27
alone
comp~ments
comp~ment
comp~ment.
~.
by
and
The prey
xanthogrammica,
M.
or in combination (Appendix III).
em) and small A. xanthogrammica
(X-1..94
em
were used so that their size range was similar to that of the A.
elegantissima used in the experiments (x-2 ..5 em sd-l.23 em).
the
For these obser­
these with strips of plastic
with and feed on the prey in the
californica,
C.
and
fifteen
One D. imbricata was introduced into each
used in these experiments were
senile
into
iso­
activity
of
the
Observations
on
leather stars were made at five to lS minute intervals
from the time the leather star was introduced until
until three hours elapsed.
it
settled
on
prey
or
Periodic checks were made at one to 12 hour inter­
vals from this time until the termination of the experiment.
Mechanical Irritation
To determine the effects of
tocysts)
on
to pinching
mechanica~
irritation (e.g. stinging by nema­
the behavior of the leather stars the reactions of leather stars
were observed.
Individua~s
were placed in a plastic
screen
box
which was carefully rotated so that they were suspended upside down on the top
and I was able to view their oral surfaces while pinching them with metal for­
ceps
( similar
to Barnes et al 1970).
One tube foot on each arm was pinched.
Then a piece of squid was placed on the screen near the mouth, and the leather
stars were allowed to evert their stomachs on the squid. At this time the tube
18
feet were again pinched, as well as the stomach lobes.
dermis
and
In addition, the
epi­
dermal papillae of leather stars in the squid tank which were not
used in feeding experiments were pinched.
19
RESULTS
stomach Contents of Dermasterias in the field
A total of 109 different leather stars were examined at
and 134 different leather stars at the breakwater.
at each location.
cora~limorphian
The most commonly taken prey
Stillwater
Of these, 66% were feeding
at
both
corynactis californica (Figure 4).
locations
feeding on C. californica.
~.
(~,
too far.
prey
item.
determine
the
californica leave no hard parts) a rough
estimate can be calculated from the few stomachs in which
progressed
the
imbricata examined at Stillwater Cove were
Although it was often difficult to
number of anemones in the stomach
was
At the breakwater, 84% of
the 92 feeding leather stars contained C. californica as the main
Similarly, 62% of the 73 feeding
Cove
The median number of C.
digestion
had
not
californica eaten per D. imbri­
cata was 10 at the breakwater (range - 5-44) and 5.5 at stillwater cove (range
=
(Table
1-22)
3).
This difference in meal size may be due in part to the
smaller size of the leather stars at Stillwater Cove and to the lower
density
of C. californica (pers. obs.).
A number of other prey species were
At the breakwater the D. imbricata ate A.
a~so
taken at each site
elegantiss~a
(Figure
(5\ of observations),
hydroids (3% of observations), bryozoans (3% of observations), and
ous
A.
items
such as crab molts or barnacles (totaling
4\
This clone was located on the top of a boulder in a
area and had five leather stars feeding within it.
mainly
Aglaophenia
sp. and Abietinaria ap.
miscel~ane­
of observations). The
elegantissima were all in the same c10ne found just outside
study area.
4).
of
the
main
very shallow
The hydroids consumed were
These hydroids were found as the
main prey in a few stomachs.
in
the
However, they were also found in
small
of many of the leather stars that were eating
stomachs
amounts
califor­
~.
nica.
Since these hydroids grew in amongst the f.
eaten
exclusively, and made up a very small percentage of the biomass of prey
in the stomachs,
californica,
seldom
were
they were not considered an important prey item.
The
bryo­
zoans consumed were mainly epiphytic on red algae.
Minor prey species consumed at Stillwater Cove were basically similar but
showed
a few important differences.
of the washrock fed mainly on
centrotus
purpuratus).
f.
These
Dermasterias imbricata found at the base
californica and purple
urchins
were trapped in
sions, preventing their escape from the leather stars.
of
the
washrock
urchins
(Strongylo­
sh~low
rock depres­
On the shoreward
side
at a depth of 15 meters the depressions (approx±Mately 3 em
deep and 5 em across) are so numerous that they
cover
the
bottom,
found
feeding
edge
to
edge.
Leather stars at Stillwater Cove were also
on
bryozoans
of observations), the sponge Tethya aurantia (5% of observations), arti­
(10%
culated coralline algae (14% of observations), chitons (1%
of
observations),
and miscellaneous items such as crab claws and dead scyphozoan medusae (total­
ing 4% of observations).
Several dives were made during the fall of 1979 and early in
number
of different locations to compare the diet of D.
Monterey Peninsula.
found
feeding on f.
During september
~979,
twenty of
californica on large rocks off
2~
~ricata
leather
f.
californica, the rest were not feeding.
found three leather stars
feeding
on
C.
at
a
around the
stars
were
Cannery Row in Monterey.
One of seven leather stars examined at Carmel River Beach in
was feeding on
1980
californica
A
at
November,
~979,
few days later, I
the
washrock
in
Table 3: Number of C. californica under the everted stomachs of
feeding Q. imbricata
Monterey Coast Guard Breakwater
radius of longest
arm (em)
number of £. californica
in stomach
6
5
8
6
9
10
10
10
10
25
10
44
stillwater Cove
radius of longest
arm (em)
~
number of C. californica
in stomach
4
1
6
4
6
5
6
6
6
7
7
l.
7
5
7
~2
9
6
10
1.2
23
stillwater Cove
(2~
meters depth) and one which was not feeding.
In January, 1980, I made another dive at the breakwater and found
imbricata feeding on
£.
californica and one not feeding.
made two dives in the Hopkins Marine Life Refuge in
stars
are
rare
l~
During May, 2980,
Pacific
Grove.
D.
I
Leather
in this area, and I was only able to find four D. imbricata.
These were at the base of a large rock covered with C.
but
were
interacting
with
ca~ifornica,
not feeding.
Behavioral Observations in the Field
Dermasterias imbricata were observed
prey
on
several
occasions.
approaching
Three leather stars were seen moving away from
partially digested C. californica at the breakwater.
stars
and
Each
was lifting at least one arm away from neighboring
£.
had attached extruded mesenterial filaments to the leather
face.
I
group of
its
c.
also
observed
a
of
these
californica which
stars'
oral
sur­
leather star at Stillwater Cove approach a small
f. californica, contact the tentacles of the anemones,
arm
leather
rapidly
lif~
and change directions, thereby avoiding any further contact with the
californica.
The solitary coral, Balanophyllia elegans,
response
in
leather stars in the field.
stars encounter
arms
and
~.
alter
also
elicited
elegans at the washrock, and each time quickly
their
avoidance
On two occasions I observed leather
movements to leave the area.
~so,
imbricata in areas of high coral abundance and did not find
corals.
an
lift
their
I seldom found D.
them
feeding
on
On four occasions when I surveyed the distr1bution of D. imbricata at
the table mount in stillwater Cove I found only one or two
leather
the
on the upper three
lower
three
meters
of
the vertical face, but
20-~8
stars
on
24
meters.
Those leather stars on the upper portion were feeding
mainly
on
C.
californica which were absent from the lower portion.
few encounters between Q. imbricata and purple urchins were observed at
A
the
washrock.
diameter urchin.
5 . J. em
humped
imbricata unsuccessfully attack a
The leather star climbed on top
the
of
urchin
and
up the center of its body so that it could surround the urchin without
touching it.
its
I watched a 12 em radius D.
spines
During five minutes of observation I watched the urchin
and
repeatedly
leather star's oral surface.
stomach
and
withdrew
reach
out
with
its pedicellaria and pinch the
The leather star did not attempt
without feeding.
flatten
to
evert
its
I found several D. imbricata in this
area with detached urchin pedicellaria attached to their oral surfaces,
indi­
eating that encounters with urchins may be fairly common.
Size Distribution of Dermasterias
The leather stars examined at the breakwater
than those at stillwater Cove
t-test).
(p=O.OO~i
were
significantly
The mean length of the long­
est arm of 60 leather stars measured at the breakwater was
em)
with
a
range
of
3.3-12.5 em.
8 . 75
em
em).
However,
the
range
( sd=-~. 52
In contrast, the mean arm length of the
longest arm of 45 leather stars measured in Stillwater Cove was only
(sd~1.98
larger
in
sizes
was
s~lar
6.91
em
to the breakwater
leather stars (4.0-13.0 em).
Prey Distribution
Corynactis californica was the only commonly found
both
..
study
•
1
p~acea ~
areas.
subtidal
anemone
corynactis californica occurred in 44 of the 52
m-? quadrats at the breakwater (Figure 5).
Almost
half (21
in
rando~y
25
quadrats)
of
these had over 25% cover.
not found in any of the quadrats. The A.
at
By comparison,
elegantiss~a
elegantissima were
~.
in the intertidal
zone
the breakwater usually occurred on the flat tops of boulders and were spa­
tially separated from the C. californica, which generally were found on verti­
cal
surfaces,
by a band of barren rock, green algae, and barnacles.
Several
large (at least lS em oral disc diameter) A. xanthogrammica were found in
study
the
area
only
but were not found in quadrats.
anemones
found
in
the
the
Corynactis californica were also
quadrats
placed
around
D.
Corynactis californica were found in 43 of 45 of these quadrats.
per cent cover of C. californica in these quadrats
did
not
imbricata.
.However, the
differ
signifi­
cantly from the randomly placed quadrats.
Corynactis californica were also the
Stillwater
Cove.
Large
most
commonly
found
anemones
elegans
However,
£.
imbricata stomachs .
Solitary
corals
( Balanophyllia
and paraeyathis stearnsi) were also found in small numbers within the
study areas.
and
Cove.
generally larger than 10 em oral disc diameter and were
were
not found as prey in
only
Only a few P. stearnsi were found in quadrats at the breakwater,
one
small
group of
~.
elegans were found near the study area.
contrast, B. elegans were more common in the Stillwater Cove study areas,
usually
in
A. xanthgrammica were found subtida.l.ly at Arrowhead
Point, and Tealia spp. were found at all sites in Stillwater
these
anemones
on
lower
portions of the rock walls than ·were occupied by
~.
In
but
imbri­
cata.
Feeding Behavior and Prey Choice in the Laboratory
When given a choice between two or more species of anemones in
the
leather
stars
consistently chose certain species over others.
the
lab,
When the
27
choice was between A. elegantissima and
and
f.
Q.
2b) 22 of 23
f.
californica
imbricata initiated feeding on
(experiments
~.
elegantissima, none on
californica, and one did not feed in 72 hours (Table 4).
as
elegantiss~a
the
first
prey
The choice of
and
Corynactis
separated from the
on
a
diet
of
~.
tanks).
diets
(squid,
It is obvious from the data that being
elegantissima for six weeks and having
squid
A.
consumed was consistent between the three
groups of leather stars which had been maintained on different
Anthopleura,
2a,
1,
been
maintained
or C. californica did not alter the prey choice of the
leather stars (Table 5).
After settling on and consuming their first prey item,
most
of
remained in the same area feeding on neighboring anemones.
imbricata
the
D.
I care­
fully mapped the movements of the leather stars in the second experiment
and
checked their stomach contents on the second day (Appendix IV b).
12 leather stars observed, seven fed on A. elegantissima
together.
These leather stars ate two to five A.
on
A.
elegantissima and then on neighboring
contac~
imbricata had been in
tiss~a
ing on
f.
californica.
from
elegantiss~a
first
~.
other
anemones.
table,
Three
£.
leather
~.
californica.
this
latter
fed
These D.
!. elegan­
elegantissma before initiating feed­
elegantiss~a
which
were
Both of these leather stars consumed the A.
and then moved to another part of the water table,
elegantiss~a
grouped
stars
californica while feeding on
Two D. imbricata fed on A.
which they encountered.
feed during these observations.
water
c.
and did not contact any other
isolated
the
with
were
Of 'the
elegantissima in succession
before moving to another part of the water table.
first
which
(2a)
settling
One leather star did not
Por the first day, after being placed in
leather
star encountered only
other D. imbricata already settled on prey.
on
f.
It then moved to
the
californica or
the
corner
of
29
the
table near the drain and ceased moving for the rest of the experi­
water
ment.
The high rate of feeding by the D.
obvious
from
data
elegantissima and C.
on
number
of
ca~ifornica,
imbricata
prey consumed.
A.
elegantissima
is
When given a choice of A.
the D. imbricata consumed all
available and very few of the C.
tiss~a
on
A.
californica (Table 6).
elegan­
Many of the
leather stars fed on more than one A. elegantissima at the same time (Appendix
IVb).
The feeding rate of the D. imbricata was consistently low for
nica
( 0 . 27-0 . 33
anemones/leather star/day).
the size and density of the C.
imbricata
in
more
Meal sizes
at a time.
In the lab, they typically ate
However, in the lab, no more than 14
£.
The
diameter=O.55 em,
9
A.
wet weight of a single
s.d.=O.22
s.d.=O.059).
size class of
s.d. s O.09).
average
em)
~.
C.
cali.­
only
necessarily
c. californica (x oral disc
0.03
g
(x
of
six
groups
of
In contrast, the average wet weight of the smallest
elegantissima
A large
was
five
elegantissima, (Table 2) and so
a meal of the same number of individuals from each species is not
five~O.166,
D.
ca.lifornica were
Also, the size range of the
was much smaller than that of the A.
equival~nt.
of
the field indicate that leather stars are capable of feeding on
consumed during a three day interval.
fornica
califor­
This is especially evident when
californica is considered.
as many as 44 anemones in a single meal.
or
f.
was
elegantiss~a
0.47
9
(l.O
em
diameter,
x-O.47
9
can weigh much more than this (51 and 67
for two 6.0 em diameter individuals).
The feeding rate of D. imbricata on
and
O. 97
anemones
per
star per day.
~.
elegantissima varied between
0.48
The variability is due in part to the
differences in the number of anemones available in relation to the
number
of
D.
imbricata
in
the
water
table,
and
differences in the sizes of A.
to
elegantissima used (Table 2).
When given a choice between A. xanthogrammica
results
were
similar.
Eight
none on C.
californica.
tained
a
on
diet
of
D.
~ricata
Of these eight
f.
and
C.
californica
settled on A. xanthogrammica and
Q. imbricata, three
had
elegantissima, and two on a diet of nothing but
over
(Appendix III). Since
weeks
from which these
had
not
been
main­
californica, three had been maintained on a diet of
squid and then A.
four
~.
squid
encountered
this
species
this, all eight settled on A.
for
xanthogrammica is rare in the area
imbricata had been collected, i t is very likely that
~.
the
in the field before collection.
xanthogrammica during the first day,
they
Despite
seven
of
these settled within the first hour (Table 7).
When presented with A. xanthogrammica,
three
californica, and
~.
senile, all
O. imbricata settled on the A. xanthogrammica rather than the other two
species.
ments
£.
These D.
because
~ricata
they
differed from the others used in previous experi­
were collected from Arrowhead Point in Stillwater Cove a
week before this experiment was conducted.
However, their behavior was ident­
ical to the sea stars collected from the breakwater.
For a week chitons (Mopalia mucosa) and snails
also
added
to aquaria containing 14 O.
~ricata.
(Calliostoma
No D.
spp.)
~ricata
were
were ever
observed attempting to feed on any of these molluscs.
When individuals were introduced into compartments containing only a sin­
gle
species
of
anemone the behavior of the D.
depending on the species of anemone prey.
tissima,
M.
senile,
and
~ricata
varied considerably
All sea stars settled on
~.
elegan­
A. xanthogrammica shortly after encountering these
species (Figure 6). The median time to the initiation of feeding for
five
D.
34
imbricata
fed
M.
senile
was
60
xanthogrammica was under 60 minutes
leather
stars.
The
median
time
minutes (range=15-120 minutes) and for
(range~60
to
first
imbricata fed A. elegantissima was higher
minutes-120
minutes)
for
~.
six
settlement on prey for five Q.
(median a 120
minutes;
range~15-480
minutes) .
This is similar to the length of time to the initiation of feeding of the
seven
imbricata
D.
originally
introduced to the Anthopleura tank.
Five of
these D. imbricata settled on A. elegantissima in the circular tank within the
first
hour,
and all seven began feeding on A.
elegantiss~a
during the first
12 hours.
This behavior differed from that of D. imbricata presented with
fornica
as the only available prey (Figure 6).
f.
cali­
The median time to first set­
tlement on prey for six of ten leather stars presented with C. ca2ifornica was
48
hours
with
a
range of 10-72 hours.
Pour D. imbricata did not settle in
three days and so were not included in these calculations.
The
D.
imbricata
in these experiments usually moved around the compartment several t1mes, often
encountering the c.
californica and obviously avoiding any prolonged
contact
with them.
The behavior of the seven D. imbricata
Corynactis tank was essentially the same.
origina~ly
introduced
C.
californica for four weeks of observation.
were consistently found on the walls of the
When
tank,
These three D.
away
from
placed on the bottom, each one climbed back up on the
tling on prey.
the
No leather star settled on C. cali­
fornica during the first day and three of the seven were not observed
on
into
the
wa~ls
feeding
imbricata
anemones.
without set­
35
Predator-Prey Interactions in the Laboratory
The defense behaviors used by each species of anemone differed in several
aspects.
The
most
obvious
differences
were
in
senile, which is the only species tested that has these
use
of
mesenterial filaments by
c.
californica.
~.
the use of acontia by
structures,
and
the
other observed differences
in response included whether anemones retracted their
tentacles
or
remained
expanded, and whether anemones released from the substratum after contact with
D. imbricata (Table 8).
I observed four attacks by
the
senile
M.
retracted
£.
their
imbricata on M. senile.
tentacles
columns as the D. imbricata began to
attacks, the D.
settle
and
On
each
occasion
extruded acontia from their
on
them.
In
three
of
these
imbricata touched the anemone's tentacles first, lifted their
arms up, and then proceeded forward with raised
arms
and
settled.
contac~
fourth attack, the leather star tolerated prolonged
In
the
with the tentacles
before settling on the anemone (at which time the anemone retracted its tenta­
cles).
Leather stars were never observed to avoid
Twenty-eight of 32
~.
contac~
with the acontia.
xanthogrammica were seen to contract
by leather stars, while only four remained expanded.
when
touched
The leather stars almost
always settled on
!. xanthogrammica shortly after first encountering them.
eight
the
occasions
leather star moved directly on top of the anemones, and
only four of the 12 observed
from
the
On
£.
imbricata were seen to lift their arms up away
anemones before settling.
substratum after being touched by a
Pour A.
leather
xanthogrammica-~
star
and
released from the
floated
upside
down
tentacles
when
because of their inflated bases.
Anthropleura elegantissima
touched
and
often
remained
did not always retract their
expanded for several hours while underneath the
37
..
stars, which were settled on neighboring anemones.
tissima
were
observed
to
On 15 occasions A. elegan­
remain expanded after being attacked by a leather
star, and several remained open for an hour or more after
On
seven
occasions
the
A.
elegantissima
retracted
being
their
settled
on.
tentacles when
touched.
Q.
Eight
imbricata were observed
elegantissima
without
settling,
encountering the anemone.
to
while
move
away
after
encountering
A.
16 were seen to settle minutes after
The anemones which
were
successful
in
repelling
attacks usually remained open and were able to touch the leather stars' aboral
surface with their tentacles.
leather
disc
fashion.
leather
caused
the
rapid
contraction
of
the
stars' dermal papillae and often the withdrawal of the leather stars'
arm from contact.
oral
This
One!. elegantissima which was exceptionally large (9. 0
diameter)
was
particularly successful at avoiding attack in this
On numerous occasions over a two month
stars
to
contact
surface by the anemone,
ClI\
period
I
observed
various
the base of this anemone, get stung on the aboral
and
withdraw
without
settling.
The
anemone
was
finally eaten by a leather star which approached it from above by moving off a
neighboring rock and on top of the anemone.
several
centimeters
above
the
The leather
star
was
suspended
floor for several minutes before the anemone
contracted its body.
When I examined the stomach contents of the leather stars at the
experiments
I
often
star (Appendix IV).
the
substratum
and
found two or more A.
Usua~ly
been
of
elegantissima in a single leather
one or more of these had apparently released from
carried away by the leather star.
digested anemones were covered in mucus and often had an
ynx.
end
These partially
everted
actinophar­
38
The greatest number of encounters observed were between D.
c.
californica.
This resulted because
c.
During one experiment, I placed four A.
patches
of
C.
californica
imbricata and
californica were often encountered
elegantissima
on
rocks
within
and allowed them to attach to the rock. These A.
elegantissima were the last to be
ea~en
by leather stars.
However, these were
eaten before the C. californica.
On six different occasions I saw leather stars lift their arms away
c.
californica
which
had
extruded
mesenterial filaments.
appeared to penetrate the epidermis and remained attached
moved.
from
These filaments
when
the
arm
was
In each case the leather star had been feeding on neighboring anemones
for several hours.
On only one occasion did I observe a leather
elegantissima
and
C.
californica
simultaneously
star
to
contact
both
A.
and then settle on the C.
39
.
. r
californica.
feeding
on
This leather star had recently
a
neighboring~.
elegantissima.
consumed
C.
californica
while
Ten leather stars settled on A.
elegantissima after encountering both species simultaneously
and
two
others
moved away without settling.
Response to Mechanical Irritation
When the dermal papillae were pinched, five
~ediately
out
of
five
D.
imbricata
withdrew patches of dermal papillae directly around the area that
was stimulated.
This was similar to the response seen in D.
imbricata
con­
tacted on the dermal papillae by other sea stars or by anemones.
When a single tube foot was pinched on the leading arm of moving
stars in the holding tank, two
...
£.
leather
imbricata lifted their arms off the substra­
tum and one continued moving without lifting the arm.
When a tube foot was pinched on each arm
within
of
the screen cage, four responses were noted.
non-feeding
D.
imbricata
Three of the nine leather
stars lifted one or two arms off the substratum away from the source of
tation.
irri­
Three leather stars did not move their arms but instead retracted all
of the tube feet on the arm and closed the opening to the ambulacral groove so
that no tube feet were exposed (Figure 7).
of these three, two exhibited this
reaction with only one of their five arms, and one
exh~ited
the reaction with
two of their five arms.
Seven D. imbricata withdrew the tube feet
tube
foot
that
arms,
adjacent
to
the
was pinched, but did not retract the tube feet on the arm on
either side of the irritation.
'~
~ediately
Of these, one exhibited this reaction on three
three on four arms, and three on all five arms.
to react to this pinching.
No leather star failed
In comparison, after the stomach was everted over squid, only one leather
star
retracted
all of the tube feet on the arm, and then only responded this
way with one of its five arms.
However,
seven
of
the
nine
D.
imbricata
retracted tube feet in the local area of irritation.
When the stomach lobes' were pinched, four D. imbricata withdrew the
at
least partially, while five gave no response at all.
dermis was pinched, none of the D.
is
significant
lobe
When the aboral epi­
imbricata gave a noticeable response.
that none of the nine
It
Q. imbricata moved away from the squid,
even when the tube feet or stomach was pinched.
The reaction instead
was
to
retract the irritated body parts and continue feeding.
Another interesting observation was that five of the nine
which
..
s~ilar
anemones.
These
to that observed in
leather
stars
Q. imbricata feeding
retracted
the
food.
After
a
a
body parts in
urchins
and
cavity
was
formed
period of five to 15 minutes, the leather stars
everted their stomachs so that the stomach lobes filled the
only
on
the tube feet located around the
mouth, and elevated the center of their bodies so that
the
imbricata
were fed squid in this experiment humped their bodies up over the squid
in a manner
around
D.
contac~
cavity
and
were
with the food. Also, the tube feet were never
used to manipulate the stomach lobes.
42
DISCUSSION
Two major patterns are evident from the data. First, Q.
non-random
a
which does not appear to be dependent solely on prey availa­
diet
The consistently low preference for f. californica as compare to
bility.
other
imbricata has
anemones
indicates
food items by the
~.
the
all anemones are not perceived as equivalent
that
Second, Q. imbricata react in consistent
imbricata.
and
obviously different ways depending on the species of prey encountered.
The non-random diet observed
in
the
laboratory
appears
to
interpret in relation to the feeding data from the field (Figure 4).
There is
an obvious inconsistency between the high frequency of feeding on C.
califor­
nica
observed
at the breakwater, Stillwater Cove, and other areas around the
Monterey Bay, and the hesitancy of D. imbricata to feed on C.
,..,
difficult
the
(Tables
lab
4, 5
and
7 and
Figure 6).
not
(e.g.
~.
commonly
found
in
of
anemones
habitats where they occur in central
light
~970,
Porter 1972,
~974,
Ormond et al 1973, 1976,
Using caging and transplantation
that
A.
elegantiss~a
interpreted
exper~ents,
Col~ins
Sebens
et
a~
~970,
1974).
(~977)
demonstrated
are capable of surviving in the subtidal zone if they
are protected from predation.
to
C~ifornia
of studies by Sebens (1977,1981) on Anthopleura sp. and by a number
of researchers on Acanthaster planci-coral interactions (Barnes
Vine
which
elegantiss~a).
These inconsistancies are only apparent, however, and can be
in
in
It also appears unusual that D.
imbricata preferentially feed on species and size classes
are
californica
However, when leather stars were allowed access
the transplants, either because they were introduced into the cages or the
transplants were not caged, the leather stars rapidly consumed
tissima.
In addition, Sebens found D.
the~.
elegan­
imbricata feeding on A. elegantissima
43
on the lower edges of the anemone clones in his study areas.
tions
led
Sebens
to
(1977)
lower distribution of
~
suggest that
These
observa­
Q. imbricata predation limits the
elegantissima in some areas.
This is similar
to
the
in
the
effects of P. ochraceus predation on mussel distribution (Paine 1974).
No large anemones were found in the
field,
although
species
apparently
or
~une
individuals
diameter)~.
imbricata
Because of this, and the
in
elegantissima
aquaria,
my
from D. imbricata predation.
~unity.
First,
imbricata are
~.
usually
by anemones which can use tentacular nematocyts to sting the leather
stars' aboral surfaces.
tracted, that the D.
while feeding.
leather
D.
of anemones may reach a size at which they are
Two factors contribute to this
repelled
of
they did occur in the study areas.
long survival of the large (9 em
some
stomachs
star
Second, some anemones are so large,
when
con­
imbricata cannot touch the substratum with its tube feet
Since tube feet are never used
would
even
to
hold
onto
anemones,
the
be vulnerable to being washed off the anemone by wave or
surge action in this situation.
Another factor which is
response
of
Anthopleura
~portant
to
However,
is
that
of
may
be
very
effective
in this case would be to remove (and
possibly
kill)
the
anemones
exper~ents,
release until after the D. imbricata had settled on them.
for
The end result
from
clones,
have the same affect as predation on the anemone population.
not all Anthopleura individuals released during my
not
in
unsuitable
reattachment (e.g. the sand plain surrounding the breakwater).
may
escape
in many areas, by employing such behavior the anemone might
well be washed away from the clone, and possibly into an area
which
the
spp. Releasing from the substratum and inflation of
the base was ineffective in the aquaria but
field.
consider
and
~so,
many
did
These anemones
44
were often carried off, allowing the leather stars to feed on
individual
simultaneously.
some of the experiments.
more
than
one
This contributed to the high feeding rate seen in
In these cases, the escape behavior of
the
anemone
actually increased the predation rate.
The sharp boundary on the lower edge of A. elegantissima clones
by
Sebens (1977) is similar to what I observed at the breakwater.
observed
The break­
water has an unusually steep slope, changing from high intertidal to 10 meters
of
depth
in
only about 50 meters of horizontal distance.
fairly protected from wave action.
move
between
As a result,
D.
This area is
imbricata
can
a~so
probably
the lower intertidal and the subtidal zone and does not have to
pass over extensive areas of sand or an active wave zone which may act as bar­
riers
to
It is very l1kely that in a situation such as this,
leather stars.
~portant
D. imbricata could be very
elegantissima distribution.
in asexual reproduction
enlarge
during
this
elegantiss~a,
In
addition,~.
and it
may
be
to
elegantissima, small
predation
Chess 1972).
g.
missed
~.xanthogrammica,
al
have been reported as prey in different areas (Mauzey et
and
that
they extend into areas frequented by
Therefore there may be a seasonal component
study.
of
A.
Also Sebens (1977) reports a distinct seasonality
in~.
t~e
at determining the lower boundary
as
clones
imbricata.
during
my
and M. senile
1968,
Rosentha~
Thus the apparent paradox of preferring prey which were not
found to occur in the study area is not a paradox at all.
The other part of the paradox can also be
explained.
C . californica
is
frequently eaten in the field (Figure 4), but is also extremely abundant (Fig­
ure 5).
The observaton that a predator may feed
heavi~y
on a secondarily pre­
ferred prey (Sensu Paine 1969) if it is very abundant while the primarily pre­
ferred prey species is scarce has been made
by
many
researchers
(e.g.
P.
45
ochraceus,
Feder
1959).
Since the diet of D.
imbricata in other areas con­
sists mainly of one or two species of very abundant prey, this observation
is
not wholly unexpected.
The variability in the behavior of D. imbricata when encountering prey is
of
interest,
and
may help to explain the observed feeding preferences.
major differences observed in
species
occur
Q.
imbricata
behavior
toward
four
prey
in the time to first settlement on prey (Figure 6) and in prey
choice when presented with more than one species (Tables 4
observations
the
The
of
the
D.
and
7).
Carefu~
imbricata during the period of initial contact with
prey confirmed that most of the sea stars contacted
C.
californica
as
fre­
quently or more often than they did other prey species presented in the exper­
iments. As a
result,
these
encounters.
Indeed,
D.
t~es
differences
are
not
due
imbricata often encountered C.
to
non-random
prey
californica several
without settling before encountering and settling on Anthopleura spp.
The main reason for the differences in feeding behavior appears to be due
to
an
active
aviodance
of
contact
with
C.
californica by
Approaching leather stars repeatedly withdrew from contact
californica,
but
seldo~y
from
other
difference in behaviors might be that the
anemones. One
g.
with
~.
imbricata.
expanded
C.
explanation for this
imbricata are reacting to irrita­
tion caused by the discharge of nematocysts by the anemones.
Three lines of reasoning support this
hypothesis.
First,
it
is
very
likely that the anemones are using nematocysts as defense since these are well
known as a mechanism used by cnidarians in defense.
tures
Some anemones have struc­
such as acontia and mesentarial filaments which contain nematocysts and
have been reported to be used in interspecific aggressive encounters
2973,
(waters
Choa 1975) and were observed to be used against the leather stars in my
46
experiments (even acrohagi were occasionally used
elegantissima).
by~.
The
anemones would not be everting, inflating, or extruding these structures after
contact by the leather star other than for their use in defense.
c.
Finally,
tocysts
than
1955a and b).
to C.
californica has much larger and perhaps more irritating nema­
the other anemone species used in these
exper~ents
(Hand 1954,
This is consistent with the stronger reaction of leather
stars
californica.
Dermasterias imbricata appears to have well developed
morphological
and
behavioral mechanisms which allow them to avoid contact between sensitive body
parts and discharging nematocysts.
For example, leather
fully
derm~
retract
their tube feet and
after contact with anemones.
papillae in
~so,
the
nudibranch
loc~ized
able
to
areas rapidly
s~liar
to
papillosa (waters ~973).
Aeolidia
be
they are covered with a mucus layer
which may entrap discharging nematocysts in a manner
of
are
Their stomach and epidermis do not appear to
sensitive to mechanical irritation.
defense
stars
imbricata often approached prey with uplifted arms,
and
the
mucus
Dermasterias
assumed
a
domelike
posture over the prey by humping their bodies and contracting their tube feet.
By doing this, the leather star presumably aviods any contact with the prey.
These behaviors and
dation
on
cnidarians
morphologica~
because
they
characteristics may be related to
are
similar
to
those
found in other
asteroids with similar diets but are not necessarily found in those
that
prey
on
molluscs.
Por example, A.
Pisaster
giganteus depend
heavi~y
asteroids
planci avoids using the tube feet
when mounting a coral head (Barnes et al 1970) while pycnopodia
and
pre­
helianthoides
upon their tube feet for prey capture.
This may help to explain why Pisaster spp.
and other
asteroids
won't
climb
~
pilings
which
are
ringed at the base by
c.
californica (Wolfson et al 1979)
47
while Patiria minata (which is very similar in many ways to leather stars) and
D. imbricata are often found amongst
f.
californica (pers. obs.).
Finally, leather stars encountering expanded anemones reacted in the same
way
as
those
that
had
been pinched with metal forceps.
In both cases the
leather stars retracted tube feet and dermal papillae, often only in localized
areas around the source of irritation, and sometimes raised arms away from the
stimulus.
stars
However, similar reactions were also occasionally used
encountering
leather
bait squid or conspecifics, and it is di£icult to explain
As
these latter observations in terms of mechanical irritation.
explanation
by
a
possible
for this odd behavior, it may be that since most prey items eaten
by leather stars in nature have defense mechanisms capable of irritating
sitive
sen­
tube feet that these leather stars use a similar, stereotypic, reponse
to all encounters.
Mechanical irritation by nematocysts does at least partially explain
avoidance of C. californica by Q.
D.
~ricata
were
unavailable.
behaviors
Hence
(e.g.
I
~.
planci (Ormond et al
which
c~ifornica
(~976)
nature
~976).
Also, I did not
found that
see
~ricata
in the lab.
~.
planci kept
in
aquaria
The frequency of the arm lifting response
no different in these experienced
~.
it
is
was
planci, but they appeared much more capa­
ble of overcoming their initial avoidance
However,
in
were initially avoided would accept them at a much higher
rate in prey preference tests.
coral.
californica
reduced arm lifting) which suggested that D.
In comparison, Ormond et al
corals
C.
Unfortunately
have no idea whether this behavior is a learned
became insensitive to contact with C.
with
in the laboratory.
which had not previously encountered
response, as it may be in
any
~ricata
the
and
settling
on
the
unpreferred
significant to note that these researchers were not
58
Appendix IV
Number and size of anemones found in the stomaes of D. imbricata
during laborabory experiments.
Dermasterias
tag sequence
anemone
species
number and
size of
anemones
time (hours from
beginning to
stomach examination)
A. xanthogrammica
(1 ) 8 em
48 hours
(radius in em)
goowb (7.7)
gowbb (7.3)
go099 (6.7)
gobog (7.7)
ggogg (7.8)
( 2 ) 5 em
( 1 ) 2 em
( 5 ) 1 em
( 3 ) 2 em
( 2 ) 2cm
(7 ) 1.5 em
gbgbo (6.2)
gooob (9.2)
bbb (9.0)
A. elegantissima
( 1 ) 1 em
(3 ) 2
(1) 2 em
oobb (9.8)
bbbo (7.5)
em
II
( 2 ) 3 em
(1) 4 em
bwo (10.S)
(1) 1.5 em
( 3 ) 2cm
(1) 2.5 em
bwb (10.5)
( 2 ) 1.5 em
( 1 ) 2.5 em
(1) 4 cm
gowb (8.5)
(1) 1.5 em
(1) 2.0 x 5.5 em
oob (8.2)
(1 ) 4cm
( 2 ) 1.5 em
b (10.2)
(1) 3cm
s-tip
0000
(1~.2)
(8.0)
..
(1) 1cm
(1) 2.5 em
(1) 2 cm
26 hours
48
able to reduce the acceptance rate of preferred corals, even by feeding the A.
planci other prey for two months.
While mechanical irritation alone may explain some of my observations, it
is
~portant
known to be
to
remember that chemical substances liberated by the prey are
~portant
asteroids (Collins
in inducing or inhibiting
~974,
Ormond et al 1976).
feeding
responses
other
in
While nothing is yet known about
the influences of chemicals on the feeding behavior
of
imbricata,
D.
this
cannot be discounted, especially since their anemone prey are known to release
biologically active chemicals into the water (Martin 1968).
The feeding behavior of D. imbricata is similar in many ways to
the
predatory nudibranch Aeolidia papillosa
waters (1973) reported that
..
A.
xanthogrammica,
but
(~ater
to
avoid
C.
for
D.
effectiveness
of
caused
part to the
species,
repelling nudibranchs.
a~
~ricata
and
size of the
and
Prey defensive
result
reported
papillosa would not con­
greater
Whereas acontia did not
they became entangled in the nudibranchs' cerata
obvious damage and irritation.
sma~l
~.
the
of
~974).
elegantissima
senile in the lab. This seemed to be due to the
acontia
obviously damage Q.
and
Unlike
imbricata, waters (1973) found that
sistently feed on M.
on~.
californica.
behavior was used to explain these preferences.
here
1973, Edmunds et al
!. papillosa fed readily
tended
that
~.
However, my results may be due in
senile used, the
the low density of this prey used.
sma~l
sample sizes for
That D.
this
imbricata can sus­
tain damage after contact with some species of anemones is evident from obser­
vations made in the field by R.
Cohen (pers. comm.).
In summary, I have found in this investigation that in the Monterey area,
the
leather
star
(Dermasterias
imbricata)
feeds mainly on C. californica.
49
Corynactis californica is a small, extremely
abundant
anemone
which
has
a
depth range which overlaps extensively with that of the leather star. However,
when other species of anemones are made equally accessible in the lab, leather
stars
consistently choose A.
elegantissima,~.
xanthogrammica, and M. senile
over C. californica.
Dermasterias imbricata do not appear to lose their preference for
pleura spp. when kept on alternate diets for up to
s~
weeks (see Landenberger
1968, Murdoch 1969, and Ormond et al 1976 for other examples of
exhibiting
strong
preferences
which
~.
it
implies that whenever leather stars encounter
xanthogrammica they would feed on them preferentially
nica.
invertebrates
do not switch to secondarily preferred
This is
prey until the preferred prey are completely unavailable).
because
Antho­
~.
~portant
elegantiss~a
or
over the C. califor­
This may reduce the ability of these anemones to extend the lower lim­
its of their distributions into areas
frequented
by
D.
imbricata
( Sebens
1977) .
Also, it is
small
anemones.
l~ely
that
~.
imbricata are limited to feeding on relatively
No large anemones were found in their diet, and the leather
stars in the lab had difficulty capturing large individuals.
few
reports
of
them
There
particularly
also
preying on large anemones and some species may have an
escape in size similar to that reported by Paine (1976) for mussels.
a
are
appealing
hypothesis
This
is
since it helps to explain, at least in
part, the scarcity of small anemones and the persistence of larger individuals
of
the
A.
xanthogrammica were absent from the subtidal zone in washington, but
abundant
same species in the subtidal zone.
Sebens (1981) observed that small
in the intertidal zone on mussles.
ever, adult A. xanthogrammica migrate into the
very
As they reach larger sizes, how­
low
intertidal
and
subtidal
50
zones
which,
imbricata.
important.
in
at
least
some areas, overlaps with the distribution of D.
Thus differential predation on the various
size
classes
may
be
5J..
LITERATURE CITED
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tors.
1974. Interactions between a sea pen and seven of
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preda­
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Rosenthal, R. J., and J. R. Chess.
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53
Appendix
I:
Description of individual £. imbricata and treatments
tag color
sequence
9 0 g09
gbgbo
~~
bwb
gog
orange
gowbo
gowob
go099
ggg
go
gg
g obo 9
bgg
ggogg
gooob
'Wob
bbbb
gowbb
gowb
gb
00
wbo
wwb
bb
000
boo
bo
booo
bbo
oob
six arm
bwbb
owb
bbbo
collection
date
9/81
9/8~
9/8/81
11/11/81
11/1~/81
9/81
9/81
9/81
11/11/81
11/11/81
11/11/81
9/81
9/16/81
9/81
9/81
9/8/81
9/8/81
9/°81
9/16/81
11/11/81
9/8/81
9/8/81
9/8/81
9/8/81
9/8/81
9/8/81
9/8/81
9/8/81
9/8/81
9/8/81
9/8/81
9/8/81
9/8/81
9/8/81
arm radius
x (sd) em
8.2
6.1
10.~
10.5
7.1
7.8
6.5
6.6
7.1
8.7
7.1
7.7
6.3
7.8
9.2
10.4
10.3
7.3
7.9
8.2
10.2
12.1
9.3
10.5
8.1
8.1
8.1
7.9
8.2
8.1
8.4
9.0
9.1
7.2
( 0 .27 )
(0. 3~ )
(0. 40 )
( 0.50 )
( O. 30 )
( 0.23 )
( 0 . 37 )
( 0.23 )
( 0.30 )
( O. 43 )
( 0 . 36 )
( o. 87 )
(0.31)
(0.34)
( 0 . 37 )
( 0.27 )
(0. 2S )
(0.24)
( O. 43 )
(0.47 )
( 0.28 )
( 0 . 42 )
( 0.15 )
(1.0)
(0.29)
(0.15 )
( 0 .13 )
( O. 36 )
(0.31 )
(0 .1~ )
( 0.33 )
( 0.22 )
(0.44 )
(0.25 )
(continued next page)
radius of
longest arm-- ( em )
*treatments
8.5
6.5
10.5
11.0
7.6
8.0
6.9
7.0
7.4
9.2
7.5
8.5
6.7
8.2
9.5
10.7
10.5
7.6
8.5
8.9
10.5
12.5
9.5
10.7
8.5
8.3
8.3
8.3
8.6
8.2
8.9
9.4
9.6
7.5
5,3
s,3
s, 2a, 21:>, 3
s,3
s,3
s,3
5,3
s,3
s,3
s,3
s,3
9,3
9,3
9,3
s,3
s,3
s,3
s,3
s,2a,2b,3
s,3
s,l
e,l
a,l
s,l
e,l
a,l
s,l
e,l
a,l
c,2a,2.b
s,2b
s,2b
s,2.b
s,2a,2b
S4
tag color
collection
date
sequence
b
9/8/81
9/8/81
9/8/81
9/8/81
9/8/81
9/8/81
9/8/81
9/8/81
9/8/81
9/8/81
10/81
oobb
bbb
bwo
I-tip
0
s.a.I.m.
ob
0000
orange arm
goowb
arm radius
x (sd) em.
9.6
9.2
8.5
9.7
10.5
9.4
7.0
8.8
7.8
8.9
7.7
(0.45 )
(0.39)
( 0.30 )
( 0 . 66 )
( O. 46 )
( 0 . 36 )
( 1.03 )
radius of
longest arm (em)
( 0 . 33 )
10.2
9.8
9.0
10.5
11.2
9.7
7.6
9.1
8.0
( O. 81 )
9.4
(0.19)
( a .35 )
8.1
'*'treatments
a, 2a, 2.b
s,2a,2b
a, 2a, 21:>
a, 2a, 21:>
c,2a,2b
c,2a,2b
s,2a,2b
s, ,2b
c,2a,2.b
s
9,3
*treatments;
s=squid tank
a=Anthopleura elegantissima tank
c=Corynactis californica tank
l-first replicate of paired ~. elegantissima/f. californica choice
experiment
2a=second replicate of paired !. elegantissima/f. californica choice
experiment
2b=modified !. elegantissima/£. californica choice experiment
3=single and multiple prey choice experiment (see appendix 2 for
details of prey composition)
55
Appendix II:
Description of £. californica used in experiments
Collection dates: 9/8/81, 9/16/81, 1~/ll/81
oral disc diameter: X=O.55 sd=O.22cm
X
n (measured)=40 Corynactis
Rock dimensions (em)
width
length
30-
34
34
5
22
5
6
29
31
34
38
87
75
27
46
26
27
38
27
36
54
61
42
19
74
22~
44
178
34
24
26
53
36
132
42
28
28
129
24
~
Number of Corynactis
per rock
21
24
32
16
17
28
x=27.9 em
52
36
p37.0 em
64
94
86
39
48
50
81
x=80
corynactis per rock
sd=12.6
sd=14.5
sd-55
56
APpendix III:
Description of Single Prey Species Presentation
leather star
tag color sequence
gowbb
*prey species
squid
Ax/CC
9gog9
squid
Ms
Ax/Cc
Cc
gobog
squid
Ms
Ax/Cc
Cc
go
squid
Cc
Cc
gooob
gbgbo
gb
squid
Ae
Ae
9/81-21/23/81
11/23/81-11/27/81
22/11/81-12/13/81
12/4/81-12/7/81
11/11/81-11/23/81
12/23/81-11/27/81
12/3/81-12/5/81
squid
11/11/81-12/4/81
12/4/81-12/7/81
squid
squid
Ae/cc
squid
squid
Cc
Cc
bwb
9/81-11/23/81
11/23/81-11/27/81
12/11/81-12/13j81
12/4/81-12/7/81
9/81-11/23/81
11/23/81-11/27/81
11/27/81-12/4/81
Cc
gowbo
9/81-12/11/81
12/11/81-12/13/81
squid
Ae
Ae
Cc
orange
exper~ent
Ax/Cc
Cc
gowb
duration of
9/81-11/23/81
11/23/81-11/27/81
11/27/81-12/4/81
12/11/81-12/13/81
Cc
gog
presented
squid
Ae/Cc
11/11/81-12/4/81
12/4/81-12/7/81
9/16/81-10/25/81
10/25/81-11/4/81
12/4/81-12/7/81
11/11/81-12/4/81
12/4/81-12/7/81
9/81-11/23/81
11/23/81-11/27/81
12/3/81-1.2/5/81
9/8/81-10/25/81.
10/25/81-11/4/81
57
Ms
Cc
gogog
goowb
squid
9/8~-1~/23/8l
Ae
Ax/Cc
11/23/81-11/27/81
12/11/81-12/13/81
squid
12/3/81-12/5/81
11/23/81-11/27/81
12/11/81-12/13/81
Cc
Ax/Cc
squid/ms
ggg
Ms
Cc
gg
gowob
11/11/81-11/23/81
11/23/81-11/27/81
12/4/81-12/7/81
squid
11/1~/81-11/23/81
Ae
Cc
11/23/81-11/27/81
12/7/81
squid
Cc
9/81-11/23/81
11/23/81-11/27/81
12/3/81-12/5/81
Cc
squid
googg
11/23/81-11/27/81
12/4/81-12/7/81
Ms
Ax/Cc
Cc
9/81-11/23/81
11/23/81-11/27/81
12/11/81-12/13/81
12/4/81-12/7/81
.~
squid
wob
bbbb
small #1
small #2
Ae
9/8/81-11/23/81
11/23/81-11/27/81
squid
Cc
Cc
9/8/81-11/23/81
11/23/81-11/27/81
12/3/81-12/5/81
squid
Ax/Cc
12/6/81-12/7/81
squid
A:x/Cc
12/6/81-12/7/81
* treatments;
squid~squid tank
Ae=!:. elegantissima
Ax=~. xanthogrammica
Cc~£. californica
Ms=M. senile
Ax/CC=~. xanthogrammic and f. californica presented simultaneously
Ae/Cc=~. elegantissima and £.
californica presented simultaneously
previous experiment (see text)
in