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ADDITIONAL INFORMATION, IF ANY, CONCERNING AUTHORS, ADDRESS, TITLE, OR CITATION DATA
PLEASE TYPE ABSTRACT DOUBLE SPACED BELOW
CRAIG, PETER C. (Hopkins Marine Sta., Pacific Grove, Calif., USA.)
The activity pattern and food habits of the limpet Acmaea pelta (Mollusca:
Gastropoda: Prosobranchia). The Veliger
Most movement and
feeding occurs when individuals are submerged at high tide or splashed
on receding tides. At night populations show a net displacement upward on vertical
rocks when the tide rises and a net displacement downward as the tide recedes.
Feeding is not continuous during periods of submersion and splash, and
individuals do not feed every high tide. A. pelta ingests a variety of
blue-green, green, red, and brown algae, both macroscopic and microscopic,
and diatoms. The most common macroscopic algac eaten are: Rhodoglossum affine
Endocladia muricata, Iridaea sp., Pelvetia fastigiata, and Egregia menziesii.
In habitats where Acmaea pelta occurs with A. limatula, the former eats mainly
larger, erect algae, the latter mainly encrusting and microscopic algae.
PLEASE DO NOT TYPE BELOW THIS LINE
The Activity Pattern and Food Habits
of the Limpet Acmaea pelta
(Mollusca: Gastropoda: Prosobranchia)
By
Peter C. Craig
Hopkins Marine Station of Stanford University
Pacific Grove, California
(5 Text figures; 1 Plate; 1 Table)
Acmaea pelta Eschscholtz, 1833, is abundant in the rocky
intertidal zone along the California coast. Described as the
most eurytopic member of the genus Acmaea by Test (1945).
A. pelta ranges in its intertidal habitat from the higher
Endocladia to the lower Egregia associations at Mussel Point,
Pacific Grove, California. Studies of its biology to date
have been concerned with its general ecology (Test, 1945), the
effects of grazing on diatom populations (Castenholz, 1961).
the reproductive cycle (Fritchman, 1961, 1962), and its eco¬
logical role in the Endocladia zone (Glynn, 1965). The pres-
ent study was conducted to provide more information on the
behavior and foods of A. pelta.
* footnote 1.
108
P. Craig
FIELD STUDIES
In order to determine activity patterns of Acmaea pelta,
l6 limpets were individually marked and observed at hourly
intervals during high tides over a continuous period of four
days. Later, another 10 limpets were observed at 30 minute
or hourly intervals for a 24 hour period. A small mark was
painted on the substrate at each end of each limpet to indi-
cate the animal's original position; at each successive obser-
vation measurement of the distance and angle of the limpet in
relation to this point gave its new position. General move-
ment, feeding activity, and degree of tidal exposure were
noted at each observation. The degree of tidal exposure was
indicated using the descriptive terms of Glynn (1965):
exposed -- periods when the animals were exposed to air with-
out wetting by waves or splash; awash -- when the animals
were wetted by the sea, but not for more than 50% of the time
submerged -- when the animals were wetted more than 50% of
the time by splash or were continually immersed. The behay-
ioral criteria used to determine the occurrence of feeding in
the field were based on observations of Acmaea pelta under
laboratory conditions, and are described later
10
P. Craig
General movement-of the population is shown in Figure 1.
Periods of movement in Acmaea pelta shows a consistent rela-
tionship with the tidal cycle. The limpets remain stationary
when out of water. Movement usually does not occur until the
end of the period when they are awash on an incoming tide.
While only three of the limpets depicted in Figure 1 moved
during the initial awash period of the higher high water, all
moved during the early part of the period of submersion.
During the following period of lower high water (Figure 1),
those animals too high on the rock to be submerged did not
move at all, although they were awash for an extensive period.
In general, A. pelta do not move until they are submerged,
though after being submerged, some were observed to move up-
ward on the rock into the zone still awash, climbing at a
rate equal to that of the incoming tide. A. pelta usually
do not remain active for the high tide period and in several
instances have been observed not to move at all (e.g. limpet
"i", Figure 1). Such stationary individuals usually move
during the following high tide.
Exact paths of movement were not plotted, but net dis-
placement on the rocks between successive observation periods
was noted for each limpet. This provides a measure of minimum
10
P. Craig
distance moved. The amount of movement and the area covered
varies considerably with individuals; one limpet moved no
more than two inches during any high tide period over a span
of four days, another covered a distance of six feet during a
single high tide period.
Figure 2 shows examples of the types of paths taken by
different individuals during a four day observation period,
Path A shows rather random movement with the limpet coming
to rest at a different spot at each exposure period. At some
time during the four day study, 11 of the 16 limpets exhibited
movement patterns like those of path B; they returned at least
ractty ha Sa
once to an-exact location previously occupied. Homing, i.e.
returning to the same exact spot and here adopting the same
orientation (Figure 2, path C), was noted in four of the
limpets. One individual homed after moving three feet away
from its spot. One limpet was observed to move into a spot
and assume the same orientation as another limpet which had
previously occupied that spot. Path D represents a type
often observed. The majority of movement repeatedly occurs
in a particular area, and the limpet returns to the same
small area (approximate diameter one inch) with each exposure
period but does not necessarily settle in the same exact spot
with the same orientation.
P. Craig
VERTICAL MOVEMENT
To test whether there was a general trend of vertical
movement on the rock surface in relation to tidal exposure,
the vertical component of movement of ten limpets was observed
at hourly intervals. The results reveal a specific pattern
(Fig. 3). When the tide rises at night a net upward dis-
placement occurs, followed by a net downward displacement as
the tide recedes. Similar movement patterns have been noted
in Acmaea limatula (Eaton, 1966) and Acmaea scutum (Rogers,
1966). Comparable data are not available for movements during
the day.
FEEDING ACTIVITY
Studies were made to determine the frequency and duration
of feeding periods, and the relation of feeding to tidal
exposure. Acmaea pelta placed in aquaria or on glass plates
covered with an algal film, and arranged so that radular
movements could be seen in ventral view, revealed a charac¬
teristic feeding behavior. The head sways from side to side,
completing a cycle in one to two minutes. This can be detected
in a dorsal view, even in the field, by watching the cephalic
P. Craig
tentacles. The mouth, if visible, is flattened and spread
over the substrate. Forward locomotion is relatively slow.
in one case about one om in five minutes. Feeding behavior
in the field and laboratory, as recorded by patterns scraped
by the radula on larger algae or on alga-covered glass plates,
corresponds with the above description. In such patterns,
produced by radular action as the limpet's head moves from
side to side, each individual rasp of the radula is visible
(Plate 1, B). At greater magnification the marks of indi-
vidual radular teeth can be seen (Plate 1, A). This pattern
of feeding provides a moderately efficient coverage of the
surface.
It was often difficult to tell whether animals were
feeding or not under field conditions, but some information
on the feeding activity of Acmaea pelta was obtained. Of the
limpets shown in Figure 1, three were not observed to feed
during the period of higher high water, and six showed neither
feeding nor other movement at lower high water. While feeding
may have occurred between observations, some limpets taken
from the field as the tide receded had no food in their stomachs
It appears that limpets do not necessarily feed during every
tidal cycle; for much of the period of activity the animals
P. Craig
move about without showing clear evidence of feeding. The
statement by Test (1945, p. 397) that Acmaea pelta "feeds at
any and all times, regardless of whether the tide is in or
out", is not supported by the present study.
FOODS OF ACMAEA PELTA
Since A. pelta is a very eurytopic organism, the question
arises whether it is able to feed on a wide variety of plant
material or feeds on a few forms which are widely distributed
in the intertidal region. Published accounts (Test, 1945;
Fritchman, 1961) indicate that A. pelta eats a variety of
algae, both microscopic and macroscopic, but quantitative
information is lacking. A study was therefore made to deter-
mine the foods available to A. pelta and the foods actually
eaten, and to assess evidences of food selection.
Acmaea pelta are most abundant in mid to upper intertidal
regions that can often be characterized by the presence of
Endocladia, Pelvetia, Egregia, or Postelsia (Figure 4). Four
areas were chosen, each a region where a different one of the
above algae predominated. Since any alga present might repre-
sent a possible food source for A. pelta, an attempt was made
to estimate the relative quantities of the different macro-
scopic algae present (Figure 5). Estimates are crude, for it
10
P. Craig
is difficult to compare the availability of an alga with a
thallus many feet long with the availability of encrusting
forms. The abundance of microscopic algae was not determined.
These forms, consisting of diatoms and unicellular and
filimentous green and blue-green algae, occurred on otherwise
bare rock surfaces and as epiphytes on many of the larger
algae in all four areas. Very small juvenile individuals of
larger algae were included with the larger algae.
Twenty five Acmaea pelta whose guts retained foodmater-
ials in recognizable states were collected from each of the
four areas. A portion of the material from the stomach of
each animal was microscopically examined. Identifications of
algae in both field environment and stomachs were made with
the kind help of Dr. Isabella A. Abbott of the Hopkins Marine
Station. An attempt was made to assess the relative amount
of each alga present to within 10%. Materials which could
not be identified in microscopic examination are listed as
"unidentified debris". The values obtained from the analyses
of the stomach contents of the 25 A. pelta from each area
were then averaged (Figure 5).
The Endocladia region, between 6.0 and 3.0 feet above
mean lower low water (Smith, 1944; a somewhat greater range
P. Craig
is indicated by Glynn, 1965), is characterized by macroscopic
red algae. In this region Acmaea pelta ingested a variety of
algae (Figure 5, A). Macroscopic algae (55%) were present in
twice the volume of microscopic algae (263). The macroscopic
algae present in the gut are not minute, immature plants but
consist of small fragments of much larger specimens. Field
observation suggests that these are probably obtained from
plants which are growing in small crevices and which have
been grazed repeatedly, and from the holdfasts of larger
plants growing on the open rock surface.
The brown alga Pelvetia characterizes a zone between
4.5 and 2.0 feet above mean lower low water (Smith, 1944).
This plant is the primary food of Acmaea pelta here (Figure
5, B). Most limpets in this region are found in the moist
area under the blades of the Pelvetia, and except for a few
small individuals they are not often seen on the blades
themselves. They apparently feed on the holdfast where
limpets are often observed during a period of submersion.
Pelvetia appeared unusually macerated in the stomach of these
limpets and is thought to constitute a large portion of the
33% of unidentified debris.
10
P. Craig
The Egregia region, occupies the 2.0 - 0.0 foot level in
the intertidal zone (Smith, 1944). Here, too, macroscopic
plants form the major part (62%) of the diet of Acmaea pelta
(Figure 5, C). As in the Pelvetia region, one brown alga
predominates in the environment and in the gut contents.
Limpets are often found directly on the holdfast and stipes
of Egregia plants, and scars apparently caused by extensive
feeding are frequently found beneath them.
This tendency of A. pelta to ingest more macroscopic
than microscopic algae is reversed in the exposed and surf-
swept Postelsia region (4.0 to 1.0 foot intertidal level;
Smith, 1944). Over half the limpets collected in this region
were taken from Postelsia stipes, but Postelsia is not the major
food found in their stomachs. They apparently feed mainly on
diatoms and other epiphytic microscopic algae growing on
Postelsia (Figure 5, D). Limpets not directly on Postelsia
also ingested quantities of Iridaea. Microscopic algae con-
stitutes 45% of the volume of stomach contents and macroscopic
algae only 32% in this zone.
Comparisons of plant foods available and stomach contents
from the four regions shows that A. pelta does not feed at
random but ingests significantly large quantities of macroscopic
/
11
P. Craig
algae. However, all the major phyla of marine plants are
represented in the diet. Jobe (1966) in a study of the
digestive onzymes of A. pelta found amylase activity marked,
and that of fucoidinase and alginase somewhat less. The
variety of foods eaten, shown in the list below, may be.an
important factor influencing the ability of A. pelta to live
in a wide range of intertidal conditions.
Algae Eaten by Acmaea pelta
(and the per cent of the 25 limpets per
region in which each alga was found)
Pos¬
Eg¬
Endo- Pel-
Regions: oladia vetia regia
telsia TOTAL
84%
100% 100%
85%
56%
I. MACROSCOPIC PLANTS
A. Green Algae
1. Prasiola meridionalis
7.12
Enteromorpha intestinalis
Ulva sp.
Cladophora trichotoma
.
B. Rec
Algae
30
Rhodoglossum affine
48
28
22
Endocladia muricata
22
ridaea sp.
12
4. Gelidium sp.
Lithothamnion sp.
12
6. Gigartina sp.
7. Dermatolithon dispar
8. Porphyra perforata
9. Peyssonelia pacifica
Brown Algae
92
1. Pelvetia fastigiata
52
2. Egregia menziesii
3. Postelsia palmaeformis
16
4. Colpomenia peregrina
5. Heterochordaria abietina
D. Flowering Plants
1. Phyllospadix scouleri
32
12
P. Craig
II. MICROSCOPIC ALGAE
1. unicellular green algae
64
84
24
diatoms, blue-green algae
2. Dermocarpa
3. Goniotrichum
sp.
8
4. Entophysalis densta
Ectocarpus sp.
Hapalosponidion gelatinosum
12
7. Pylaiella gardneri
Where different species of the same genus occupy the same
general area and habitat, and are more or less sympatric, the
extent to which they compete for various requirements is always
of interest. Acmaea pelta is often found in company with other
species of Acmaea, especially Acmaea limatula. In a study of
the foods of A. limatula, Eaton (1966) found that A. limatula
ingests primarily the red encrusting algae, Hildenbrandia,
Peyssonelia, Lithothamnion, Lithophyllum. In contrast A. pelta
eats very little of these species. The dictary studies suggest
that in situations where both species occur, there is relatively
little competition for food.
SUMMARY
1.
Most movement and feeding of Acmaea pelta occurs while
the animals are submerged and while they are being
splashed during tidal ebb. At night, the population
13
P. Craig
shows a net upward displacement when the tide rises and
a net downward displacement as the tide recedes. All but
one of l6 limpets observed over a four day period returned
at least once to an exact location previously occupied.
but only four of them consistently homed.
Feeding is not continuous during periods of activity.
2.
and apparently animals do not feed during every tidal
cycle.
3.
Acmaea pelta ingests a wide variety of algae, both
microscopic and macroscopic. The most common macroscopic
plants caten are the red algae Rhodoglossum affine,
Endocladia muricata, and Iridaea sp., and the brown
algae Pelvetia fastigiata and Egregia menziesii
4.
Acmaea pelta and Acmaea limatula often occur in close
proximity. Dietary studies suggest that in such situ-
ations there is relatively little competition for food.
ACKNOWLEDGMENTS
I would like to extend my sincere appreciation to
Drs. Donald P. Abbott and Isabella A. Abbott of the Hopkins
Marine Station for their kind help and dedicated interest.
14
P. Craig
This work was made possible by Grant GY806 from the Under-
graduate Research Participation Program of the National
Science Foundation. The photographs in Plate 1 were taken:
by Mr. S. E. Johnson.
-18-
P. Craig
Litcrature Cited
Castenholz, Richard W.
1961. The effect of grazing on marine littoral diatom
populations. Ecology 42(4): 783-794.
Baton, Charles m.
1966. The activity and foods of the file limpet Acmaea
limatula. The Veliger
Fritchman, Harry K.
1961. A study of the reproductive cycle in the California
Acmaeidac. Part III. The Veliger 4(1): 41-47.0.
1962. A study of the reproductive cycle in the California
Acmeidae. Part IV. The Veliger 4(3): 134-140.
Glynn, Peter W.
1965. Community oomposition, structure, and interrelationships
in the marine intertidal Endocladia muricata - Balanus
glandula association in Monterey Bay, California.
Beaufortia
12(148): 4-196.
.
Jobe, Alan
1966. A study of morphologic variation in the limpet/
Acmaca pelta.
The Veliger
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P. Craig
Rogers, Donald A.
1966. The effects of light and tide on the movement of
the limpet Acmaca scutum. The Veliger ():
Smith, Gilbert M.
1944. Marine algae of the Monterey Peninsula. Stanford
Univ. Press; ix + 622 pp.
Test, Avery R.
1945.
Ecology of California Acmaca. Ecology 26(4): 395-405.
Footnote, page 1.
Permanent address!
19
P. Craig
Plate 1
A.
B.
(8
P. Graig
Plate Caption
Dhetegrephe-byS.1Johnsen)
Radula pattern of Acmaca pelta produced by a limpet
feeding on a glass plate covered with a film of
microscopic green algac and diatoms.
Portion of a blade of Iridaca taken in the field.
An A. pelta was found on top of the radular marks, and
lridaca was almost exclusively present in its stomach.
-19-
P. Craig
Figure Captions
Figure 1
Movement and feeding activity of ten Acmaea pelta observed
at thirty minute or hourly intervals over a period of 24 hours,
May 4-5, 1966. Limpets are indicated in order of their vertical
positions on the rock surface; individuals lower on the rock were
awash and submerged for longer periods. The extended time during
which the two highest limpets were awash on the receding higher
high water was due to downward movement of these aimals on the rock.
Figure 2
Representative tracks of four individual Acmaea pelta on a
vertical rock surface over a period of three days, May 26-28.
1966. For cach track, each type of line represents movement during
one complete tidal cycle, and the limpets were exposed only at
lower low water. Points enclosed by small squares are the places
where the limpets remained stationary during periods of low water.
Consistent homing behavior is indicated by the track in Figure 2. C.
Figure 3
Net vertical displacement of the ten limpets in Figure 1 at
successive intervals during one nighttime higher high water, May
4-5, 1966. Bach bar represents approximately the movement during
one hour. Differences due to different vertical positions of the
limpets have been compensated for by independently calcufating
the movement each animal underwent during the phases of tide
indicated.
20
P. Craig
Figure captions (conf'd)
Figure 4
Horizontal and vertical distribution on a diagrammatic
transect of a rocky shore, showing the main zones where Acmaea
pelta occurs. Bach zone is characterized by a predominating
species of alga. Vertical ranges of the algae are based on
Smith (1944).
Figure 5
The foods available and the foods caten in four regions.
each characterized by a predominating alga, where Acmaea pelta
is abundant. "No Macro." refers to areas devoid of visible
macroscopic algae. These areas may contribute a portion to
the microscopic algae eaten; other microscopic algae occur as
epiphytes on larger plants.
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