Connor
Interactions under Pel
page 2
INTRODUCTION
Chitons and limpets represent two different classes of the phylum
Mollusca; yet they seem to perform very similar functions in the intertidal
community. They are slow-moving, grazing herbivores occurring together
throughout the intertidal. The similarity of their food and habitat
provoked a closer investigation of their apportionment of resources
within the sympatric areas.
In the portion of the intertidal zone of the central California
coast marked by the brown alga Pelvetia fastigiata (J. G. Agardh) DeToni,
two common species each of chitons and limpets can be found: Cyanoplax
hartwegii (Carpenter, 1855) and Mopalia muscosa (Gould, 1846), and
Collisella pelta (Rathke, 1833) and Collisella limatula (Carpenter, 1846).
While Cyanoplax can be found in its greatest abundance in this area
(Ricketts and Calvin, 1968), C. pelta, C. limatula and Mopalia can be
found throughout the intertidal (Test, 1945; Andrua and Legard, 1974).
Eaton (1968) and Craig (1968) distinguished the different food preferences
of Collisella limatula and C. pelta.
To identify habitat differences among these intertidal herbivores,
I conducted a general survey of their spatial distribution and of the
behavioral aspects of resource apportionment. The study was
conducted from April to June, 1974 in the high intertidal of three areas
of Monterey County, California: Mussel Point, Point Pinos and Carmel
Point. All three intertidal areas consist of granite rock outcroppings
surrounded by sand.
CONNOR
DIFFERENCES BETWEEN CYANOPLAX AND MOPALIA HABITATS
Transects were run at Mussel Point and Point Pinos through the
Pelvetia zone. Quadrats 30 cm x 30 cm were placed along the transect
with additional quadrats extending laterally to the entire width of

e rocks touched by the transect. The number of chitons and limpets
inside each quadrat was recorded.
These transects (Figure 1) indicate that Cyanoplax is more
abundant in the areas more protected from wave shock: higher rocks.
crevices and the shoreward side of rocks. Mopalia occurs at the lower
boundary of the Pelvetia zone in regions less protected from waye
action and at a lower tidal level. The limpets are found throughout
the transects.
At Carmel Point a survey was made at the same vertical height on
the protected and open sides of the point. On the protected side of
the point, Cyanoplax can be found at densities of 5-6/m?; while on
the open-coast side of the point, only Mopalia at a density of 1-2/m
1e
can be found under-Peivetia-of a similar tidal height. The sand grain
size on the open side of the point (mdø- -.991) is much larger than
on the protected side (md?-.453) where Cyanoplax is found (Figure 2),
While relative wave motion or wave shock cannot be precisely
determined from differences in grain size (Shepard, 1963), differences
as large as those observed between the two sides of the point indicate
that large differences in wave energy must be present in these two
habitats (Krumbein, 1944-1947).
CONNOR 4
FOOD COMPETITION BETWEEN CYANOPLAX AND COLLISELLA LIMATULA
Chitons in the Pelvetia zone at Mussel Point and Point Pinos
were randomly chosen; their position and the positions of the
chitons and limpets were noted and the body length of each animal
was recorded. Mapping of chiton neighbors (Figure 3) indicated
Collisella limatula to occur significantly further away (- 12.19 cm;
Student's t-test: Pf.05) from Cyanoplax than Cyanoplax was from
itself (x - 10.74 cm). C. pelta showed no such effect (X - 11.49 cm;
.2ePc. 4).
Size studies (Figure 4) demonstrated that Collisella limatula
within 20 cm of Cyanoplax were significantly smaller (X = 1.50 cm;
Pe.Ol) than C. limatula at least 50 cm away from the nearest
Cyanoplax (X = 1.80 cm).
Work by Robb (1974) has indicated that Cyanoplax hartwegii
found under Pelvetia has a diet consisting mostly of Pelvetia and
secondly Hildenbrandia occidentalis Setchell. Collisella limatula
depends mostly on Hildenbrandia and other crustose algae for its
food (Eaton, 1968) while Collisella pelta under Pelvetia eats mostly
Pelvetia and other frondose algae (Craig, 1968). Given the common
ha
elver
occurrence of large stands of thisaga in the intertidal, Pelvetia
is probably not a limiting food, but Hildenbrandia is less abundant
by several orders of magnitude. Food competition, then, may account
for the tendency of Collisella limatula to be further away from
Cyanoplax and to be larger when Cyanoplax is not in its immediate
vicinity.
Connor
page 5
HOMESTTE CONPETITTON BETUEEN CYANOPLAX AVD COLLISELLA PELTA
Data shown in Figure 3 was subjected to statistical analysis to
determine the degree of specific and interspecific aggregation. Clumping
around individuals of Cyanoplax is evident; Cyanoplax apparently occurs
mostly in the vicinity of other Cyanoplax (C-test - 58.3), but Collisella
limatula (G - 14.9) also show a significant tendency to aggregate near
Cyanoplax (P6.001). The difference between Cyanoplax's and C. pelta's
clumping cannot be distinguished (Arcsin transformation of percentages of
the total number of animals within 10 cm of the chiton (Box 16.10, Sokal
and Rohlf, 1969): .18 PC.2); while Cyanoplax shows significantly more
clumping with other Cyanoplax than with C. limatula (.OIC.PK.05).
Evidently there are certain locations on the rocks which are favorite
resting areas for the organisms, but within these favored areas comparative
exclusions can occur. Lyman (1975) has shown different Cyanoplax individuals
to repeatedly use the same set of home areas and these results suggest
that Cyanoplax and Collisella pelta might compete for these specific
home areas. When the number of C. pelta on a rock face also containing
Cyanoplax and C. limatula was experimentally doubled (from 6/ .1 m' to
12/ .1 m') in an area commonly used for homes by Cyanoplax, Cyanoplax
density decreased (Figure 5). Collisella limatula was not affected. When
the C. pelta were removed, the Cyanoplax returned. Observations suggested
that appropriate sites were occupied on a "first come, first served" basis.
CONNOR 6
EXCLUSION BEHAVIOR OF MOPALIA MUSCOSA TOWARDS COLLISELLA PELTA
While the density of Collisella limatula within 20 cm of Cyanoplax
was the same as its density near Mopalia (16.7/m2; see Figure 3),
Collisella pelta was much less dense in the vicinity of Mopalia (10.7/m2)
than around Cyanoplax (21.7/m2; G-test of independence: .Ol«p..025).
C. pelta within 20 cm of Mopalia were significantly smaller (Figure 4;
X = 2.39 cm; P«.05) than those at least 50 cm away from Mopalia (X - 2.75 cm).
In order to test whether Mopalia selectively excludes Collisella
pelta from its immediate area, C. pelta from a similar habitat were
placed one cm from the girdle of a submerged Mopalia. A control
C. pelta was placed on a matched substrate about 20 cm from the Mopalia.
After one hour the distance of the C. pelta from its starting position
was measured. In the ten trials run (Figure 6), the C. pelta near the
Mopalia always moved further (Mann-Whitney U-test: X - 9.8 cm;Pe.001)
than the controls (X - 3.0 cm). Contact did not seem to be a prerequisite
for moving, but in half the cases the chiton was seen to actively push
the limpet away with its girdle. This behavior was also twice observed
naturally in the field. C. pelta was the only animal observed to be
actively excluded by Mopalia. When Cyanoplax and Collisella limatula
were placed next to Mopalia, no reaction occurred.
Feeding studies of Mopalia muscosa (Barnawell, 1954; Boolootian,
1964; Smith, 1974) show that Pelvetia is not a source of food for
M. muscosa. Mopalia must rely on less abundant stands of Gigartina
papillata (C.A. Agardh) J.G. Agardh or Endocladia muricata (Postels
and Ruprecht) J.G. Agardh in the Pelvetia zone. As mentioned earlier,
Collisella pelta in this intertidal zone has been reported to eat
primarily Pelvetia; however, C. pelta in other zones eats both Gigartina
and Endocladia. The incursion of C. pelta, then, could represent a threat
atively limited food supply.
to M
CONNOR
MOVEMENT DIFFERENCES AMONG THE LIMPETS AND CHITONS
In the Mussel Point area, I selected a rocky outcropping covered with
Pelvetia, under which Cyanoplax hartwegii, Mopalia muscosa, Collisella pelta
and Collisella limatula were found. Movement of these animals was observed for
two 24-hour periods, one 48-hour period and one 60-hour period, The moyement
of thirteen Cyanoplax was plotted every hour during the 48-hour and the 60-hour
watches. The movement of eleven C. pelta was plotted over a 36-hour period, and
the movement of five C. limatula was plotted over a 60-hour period. Positions
of all animals were checked every hour (Figure 7).
Field observations of Cyanoplax movement (Lyman, 1974) and Collisella
pelta (using scoring method of Lyman, 1974) movement showed the two species
to be quite similar. Both moved more at night, and more when either awash or
exposed than when submerged (C. pelta average movement- night, 1.2 cy; day,
.3 cy; Pe.001: exposed, 1.1 cw; submerged, .5 cy; Pc.01). Collisella limatula,

on the other hand, moved more when submerged or awash (x - 1.8 cp) than when
dry (x - .3 cy; Pc.001), but moved equally during the night and day (.5cPf.75).
Eaton (1968) has also observed greater submerged movement in C. limatula,
and Smith (1974) observed Mopalia muscosa to move mostly at night when submerged.
While Cyanoplax, Collisella limatula and Collisella pelta all show some
degree of specific homing (Lyman, 1974; Eaton, 1968; and Craig, 1968), Cyanoplax
is the most nomadic of the three species. To quantify this movement, plots
were made of the distance of each animal from its starting point after 24 hours
(Figure 8). The traveling distance of Cyanoplax (X = 13.4 cm) was much greater
than that of either C. pelta (X - 3.8 cm; Mann-Whitney U-test: Pc.001) or
C. limatula (X = 4.3 cm; Pæ.001). No difference could be distinguished between
C. pelta and C. limatula (.4eP.5), which move more erratically within the
same general area. Average movement of the animals during the entire study
was Cyanoplax - 1.3 cm/hr, C. limatula - 1.1 cm/hr, C. pelta - .8 cm/hr; a
difference insufficient to totally cause the above results.
CONNOR 8
DISCUSSION
Hutchinson (1957) has proposed that two sympatric species will
coexist only if each
exploits some aspect of the common environment
in a different way. If limiting, the environment must be partitioned
in terms of food preference, food procurement and the requisite
microhabitats necessary to tolerate physical and biological stresses.
The evidence presented here combined with other findings can be
used to demonstrate that these four intertidal herbivores partition
their environment by food preference, spatial restriction, and temporal
restriction. This evidence is summarized in Table I. In instances of
potential resource competition, mitigating factors separate the niches.
For example, Mopalia and Collisella pelta may be potentlal food
competitors; but their activity varies with submergence, and Mopalia's
aggressive behavior forces C. pelta to occupy different areas. Cyanoplax's
nomadic behavior, as opposed to the home area behavior of the limpets,
spatially limits its disturbance of the food niche of Collisella
limatula, and distinguishes it from C. pelta which retains individual
home areas for longer periods of time than Cyanoplax.
The results of this survey therefore seem to support the generally
accepted ecological principle that congeneric species (Paine, 1962;
Kohn, 1959; Bowers, 1964; Jeffries, 1966; Haven, 1971) and confamilial
species (Magnum, 1964; Croker,1967) will show definite niche separation
despite apparent similarities in habitat and behavior.
CONNOR 9
SUMMARY
Niche partitioning by the chitons Cyanoplax hartwegii and
Mopalia muscosa, and the limpets Collisella limatula and Collisella
pelta, two classes of molluscs with similar functions in the intertidal
community, under the brown alga Pelvetia fastigiata was studied. Cyanoplax
and Mopalia were found to partition a common habitat by different
microhabitat preferences and behavioral patterns. Food niche overlap
with C. pelta was lessened by Mopalia's aggressive behavior. Food
niche overlap with C. limatula and resting area overlap with C. pelta
were lessened by Cyanoplax's nomadic behavior.
CONNOR 10
ACKNOWLEDGMENTS
This project would never have been completed were it not for
Mr. Charles Baxter, whose widespread knowledge of biology and
unfailing interest and support for the project sustained me through
the doldrums that are a part of any hard work. I would also like to
thank the rest of the HMS staff, particularly Dr. Robin Burnett who
worked on this paper as if it were his own.
CONNOR !!
LITERATURE CITED
Andrus, Jon Kim and W. Bill Legard
1974. Description of the habitats of several intertidal chiton
species (Mollusca: Polyplacophora) found along the Monterey
Peninsula of central California. The Veliger
Barnawell, Earl Baker
1954. The biology of the genus Mopalia in San Francisco Bay.
M.A. Thesis. Univ. of California,Dept. of Zoology, Berkeley. 85 pp.; 9 figs.
Boolootian, Richard A.
1964. On growth, feeding and reproduction in the chiton Mopalia muscosa
wiss
of Santa Nonica Bay. Helgoländer Meeresuntersll: 186-199;3 figs. (December 196t)
Bowers, Darl E.
1964. Natural history of two beach hoppers of the genus Orchestoidea
(Crustacea: Amphipoda) with reference to their complemental
distribution. Ecology 454:677-696; 10 figs.
Craig, Peter Christian
1968. The activity pattern and food habits of the limpet Acmaea pelta.
The Veliger 11, Supplement:13-19; 5 figs.; plt. 1
Croker, Robert A.
1967. Niche diversity in five sympatric species of intertidal
amphipods (Crustacea: Haustoriidae). Ecol. Monogr. 37(3): 173-200; 20 figs.
Eaton, Charles Mckendree
1968. The activity and food of the file limpet Acmaea limatula.
The Veliger 11,Supplement: 5-12; 7 figs.
Haven, Stoner Blackman
1971. Niche differences in the intertidal limpets Acmaea scabra and
Acmaea digitalis (Gastropoda) in central California. The Veliger
13(3): 231-248; 10 figs.
Hutchinson, G.E.
1937. Concluding remarks. Cold Spring Harb. Symp. quant. Biol. 22:
115-427
CONNOR 12
Jeffries, H. Perry
1966. Partitioning of the estuarine environment by two species of
Cancer. Ecology 47 (3): 477-481; 5 figs.
Kohn, Alan Jacobs
1959. The ecology of Conus in Hawaii. Ecol. Monogr. 29(1):47-90; 30 figs.
Krumbein, W.C.
1944-47. Shore processes and beach characteristics. U.S. Army Erosion
Board Tech. Mem., (3), 35 pp.
Lyman, Betsy Wentworth
1974. Activity patterns of the chiton Cyanoplax hartwegii (Mollusca:
Polyplacophora). The Veliger
Mangum, Charlotte Preston
1964. Studies on speciation in maldanid polychaetes of the North
American Atlantic Coast. II. Distribution and competitive interaction
of five sympatric species. Limnol. and Oceanogr. 9: 12-26; 3 figs.
Paine, Robert Treat
1962. Ecological diversification in sympatric gastropods of the genus
Busycon. Evolution 16: 515-523; 1 fig. (2 March 1962)
Ricketts, Edward F. and Jack Calvin
1968. Between Pacific tides. 4" ed. Revised by Joel W. Hedgpeth.
xiv + 614 pp.; illus. Stanford, Calif. (Stanford Univ. Press)
CONNOR
13
Robb, Mark F.
1974. The diet and feeding schedule of Cyanoplax hartwegii
(Carpenter, 1855) in various intertidal habitats with remarks on
taxonomy. The Veliger
Shepard, Francis Parker
1963.
Submarine geology. 2nd ed. with chapters by D.L. Inman and
E.D. Goldberg. xviii + 557 pp. New York, N.Y. (Harper and Row
Publishers)
Smith, Suanne Yvonne
1974. Temporal and spatial activity patterns for the intertidal
chiton Mopalia muscosa. The Veliger
Sokal, Robert R. and F. James Rohlf
1969. Biometry. xxi + 776 pp.; illus. San Francisco, Calif.
(W.H. Freeman and Co.)
Test, Avery Ransom (Grant)
1945. Ecology of California Acmaea. Ecology 26 (4): 395-405
CONNOR 14
FIGURE CAPTIONS
Figure 1. Distribution of Cyanoplax and Mopalia along transects run
through the Pelvetia zone. Numerals and bar graphs show number of Cyanoplax
per 30 cm x 30 cm quadrat. Darkened circles represent single Mopalia
individuals.
a, Topographical map of rock at Point Pinos. Contour lines represent four
inches of vertical displacement.
b. & c. Cross-sectional representation of transects at Mussel Point viewed
perpendicular to the surf line. The bars of the graphs represent the number
of Cyanoplax in laterally adjacent quadrats at the same vertical height.
Figure 2. Particle size of sand grains on two sides of Carmel Point.
The Pelvetia zone is at the same vertical height on both sides of the point.
Figure 3. Distance from chitons to all neighbors within 20 cm. Density is
the interpolated density of animals around each chiton (animal number/ m2).
a., b. & c. represent distance from each Cyanoplax to other Cyanoplax (a.),
Collisella limatula (b.) and Collisella pelta (c.).
d. & e. represent distance from each Mopalia to C. limatula (d.) and
C. pelta (e.).
Figure 4. Size frequency of limpets within 20 cm versus those more than
50 cm from the nearest Cyanoplax or Mopalia.
Figure 5. Effects of changing Collisella pelta density on the number of
Cyanoplax in a commonly used home area. Normal C. pelta density was doubled (J),
or all C. pelta were removed (*).
CONNOR 15
Figure 6. Exclusion of Collisella pelta by Mopalia. Abscissa is distance
moved after one hour by C. pelta placed one cm from Mopalia's girdle.
Controls were placed on a matched substrate about 30 cm away.
Figure 7. Movement of Cyanoplax hartwegii, Collisella limatula and
Collisella pelta in relation to tidal cycle and day-night cycle. Observations
were conducted in the field every hour for 60 hours for Cyanoplax and
C. limatula, and 36 hours for C. pelta. Cross-hatched area represents
night. S - submerged; D - dry; and shaded area - awash. Cyanoplax data
collected in conjunction with Lyman (1974).
Figure 8. Distance travelled from starting point after one day for limpets
and Cyanoplax.
CONNOR 16
TABLE LEGEND
Table I: Ecological and behavioral differences in four Pelvetia¬
zone herbivorous molluscs.
2-

00
80
o

0
D.
aa-
0
a-
99999
ataaaa-
8

Seo
(onr-able
ktaa-
—
1
alp
o
N
1/o
O
1 0
7
0
0
3
1
V
8







1F7.
X
He
lan
AlIH

Aleft fransect
4-
-center fansect
1 F.
L
Enght transeet
al,
2. left arsect
Enght fansect
0/

tallki
kl
(onwor
6-
.2-
5-
-
3-
1-
o-Fyyre 2
PeoTectp S
Cyovopnx (51m) under Peletia
moh -.433


19 06 -9 29
30 29
GRAN 5126
OeEN-CORST SiRE
CYANOPIAX RBSENT
Moeauatwote Peivene
d--.90
28 19 09 9 -20
GRAI SI22
15-
10
5-
15-
jo¬
15
5.
J0
10-
5-
DSTANCÉ FRom YANOPX (n:60)
CVANOPLEX
X = 10.74 cm
Pensty- 16-7/m
1o )5 20
b.
OCMREP UMPT
22 12. 19 o

Denstty-16.7/m

—
5 10 15 20
Rempen PeT
ot
X - I.4
Penshy- 21. 7/m
5 10 | 15 20
DISTANCE FROm VOPRE
OemRER Um
5-13.07

Denzty-16.7/m
Fon
5 | 10 15 20
X=12.00
Rempen PeR
Pnsty-10.7

E

one-pgre
jo-
jo-
5.
)0
5-
10-
5-
Coneyre
Pemaea lmatola
(rear Cyansplas)
X-1.502
LAn
6 10 14 18 72 2.6
(250 em from Cpla)
X-1.805
Al allnl
6 10 14 1.8 21
5126 (cm)
Gemaea pelfe
(near Mogalia
L HE
16 10 2.7 2.8 32
(250em from Vopalia)
Lanna
16 20 27 28 3.2 3.6
Sie (cn)
2

Day

8 10 12 17
Conro e
§ 2
ge 6
Aemaen pelta ohted
near Vpal
-Control
1Aata
I
15
DTANCÉ MOVED AFTER ONÉ POOR
(om)
S44.6
a0
ao¬
2.0
4
2

51
101 3 I0
.


I
1
U
l
952
CnOP

L
PemDEA LIMDTDIN

Hemnen Pen
CYRNOPIA
10
X =13.4 o
L
—
30
20
Pempen Ptn
10
X -3.80m
M
10
30
20
10-
Remeen um
X - 4.3cm

L
10
20
30
DSTRNCE TRRVELED FRom
SPRTNE POMT RETER 24 hrs.
(om)
(onnot-fqe 8