17
THE ACTIVITY PATTERN OF Tegula funebrali

Mark W. Howe
Hopkins Marine Station, Stanford University
s seat fp
The activity pattern of the black turban snail, Tegula funebralis (A. Adams, 1851)

at Pacific Grove, California, is the subject of this article. Field studies were
carried out to follow the locomotory and feeding activities of individuals of
T. funebralis to determine how much of each animal's time was spent in each of
these activities, and when and under what environmental conditions they occurred.
Field observations of Tegula funebralis in this study were carried out in the
tide pools on the N.E. side of lussel Point at Pacific Grove, California. The
intertidal substrate herd is composed of granite cutcroppings and boulders;
depressions are filled with coarse sand and shell fragments. The vegetation is
primarily Gigartina (Agardhii and leptorhynchos), Peyssonnelia, Ralfsia, and a thin
green algal film. Any heavy surf is broken up before it reaches this area by an
offshore granite reef. Inshore ocean temperatures varied from aboût 11 to 14°0
during the period of observation, 25 April to 1 June, 1963.
Four individual Tegula funebralis were chosen to followy in detail. Their sizes
are given below.
Specimen A—greatest basal diameter- 19m
19mm
Spedimen B
21mm
Specimen C
18m
Specimen D
Each specimen was marked for better visibility by(a) cementing a distinctive geometric
2
Mark Howe
figure made from reflector tape to the shell and (b) by cementing a wire eyelet
to the shell and attaching a 10 cm length of brightly colored thread to this, making
the animal visible even though buried among algae, rocks, or other snails. These
animals were replaced in the same tide pool area from which they had been collected
be
at approzimately 3 feet above mean lower low water, and observed for periods at
frequent intervals.
In organizing the notes taken from these observations, a system for graphing

the information was developed so that important relationships could be more readily
seen. Fig. 1, which covers a complete tidal cycle, is representative of my findings.
It represents a systematic diary of the activities of the animals which could be
followed, and of some of the environmental conditions. Data are recorded as follows.
persod
(à) The exact times of actual observation, are shown by a black line at the top of
Fig. 1.
(b) Meteorological conditions and surf indicate the approximate conditions of sky and
sea during the period of the observation.

(c) The symbols for locomotion indicate occurence of this activity. When at the
beginning of a peroid of observation a given animal occupied a different position
than that noted at the end of the previous observation, locomotion was indicated as
present but not observed.
(d) Feeding activity is also indicated in Fig. 1. It was never easy to det
dack fae
exactly when the animals were feeding and when they were not. Preliminary studies
of animals in laboratory aquaria revealed several different techniques for determining
presence or absence of radular motion and these were used as indications of feeding
s seen
in the field. When ebserving Tegula funebralis from above, the mouth area fan-be-
viewed
observecto spreadswith each stroke of the radula. If ebserving from the side and
a profile of the mouth area is exposed, the movements of the buccal mass produce a
indentation anteriorly on the head at each stroke. Where conditions did not permit
observing the above actions I sometimes had to depend on the rhythmic halting loco¬
motion or rhythmic motion of the shell characteristic of a feeding animal, of on
rhythmic motion of an algal substrate as an indication.
(e) The position symbols show the relative position of the snail on the rock substrate.
(f) The degree of immersion symbols show whether the smail was continuously
submerged, awash, or out of water entirely.
(g) Height of tide is a graphis representation of the tidal curve, based on tide table
predictions and application of the one-quarter-one-tenth rule.
er
One of the first relationships noted was the lafge numbers of animals on submerged
horizontal rock surfaces at high tide. Fig. 2 shows the behavior of three individuals,
indicating their positions onhroeks under various conditions. When out of water
they tend to occupy such sheltered spots as under rocks and in crevids, which Mad
offer some protection from dessication. As shown in Fig. 2, no animals out of water
17
Mart Houe
wick
were found on the tops of rocks, and the single individual whe remained on a vertical
surface was well protedted by Gigartina. However, many snails start to climb
vertical rock faces as soon as the incoming tide submerges them. They follow the water
level,and hence tend to cluster on the tops of rocks submerged at high tide,and in
belts around the sides of rocks not wholly submerged at hégh tide. This tendency
to climb with the tide is borne out by the increasing percentage of time spent on
Sa 8
vertical and horizontal rock surfaces at times when therare submerged. They then
nese
follow the recegding water level badk down the sides of the rocks when they are
awash at the ebb of the tide.
This(Characteristic)massing of Tegula funebralis on submerged horizontal surfaces
is less(tæ during the day than at night, however. Fig. 3 shows the results of an
experiment, conducted in a cloudy day, in a greenhouse aquarium. This aquarium was
Eleven
provided with running seawater and held at a constant water level. -11 animals
(3 large, 2 medium, and 3 small and 3 minute) were individually marked and placed
in the aquarium. Observations were made at half hour intervals and displacement ut
or down since the previous observation was noted by an upward or downward arrow in
Fg.2
the field noted. Each bar represents the sum of the number of times animals were o
observed to have moved upward and downward in a 2 hour period. There appears to
be a correlation between time of day and the upward vs. downward movements of
T. funebralis. The figure indicates a slight but definite downward activity about
Hart fowe
5
sunrise and a corresponding upward activity about sunset. This situation is
nobce
borne out by observations in the field where one can observe large numbers of
the animals on the submerged horizontal surfaces at night but fewer during the
day.
On the sample field record (fig. 1) it is apparent that feeding took place
only when the animals were wet. These and all other field observations on
feeding are shown graphically in Fig. 4, which records the percentage of each
animal's total feeding time which was spent under each degree of immersion.
Most of the time when the animals are feeding they aressubmerged. About one
third of feeding activity occurs while the animals are awash. Feeding activity
out of water onlu occurs immediately following the awash state and is negligible.
waths
In general, in the low tide situations typical for the individuals followede
of any kind
no activity/was present. In contrast, during much of the time the animals
were submerged or amash, they were either moving or feeding or both. There is
an important exception to the above generalizations, however. This occurs
in the special case of the high spring tide. Fig. 5 shows field observations
nade during two spring tides, both over 5 feet. In each case feeding and other
activity ceased during the peak of the tide. The only locomotion shown occurred
when the snail was washed loose and forced to move to regain the rock.
C
Mark Howe
Captions for figures
Fig.1 Behavior of Tegula funebralis under natural conditikns. The symbols
at the bottom of the figure represent environmental situations/ and the
position or redponses of the animals,
Fig. 2. Position of T. funebralis under various degrees of immersion.
Fig. 3. Movements of T. funebralis in an open greenhouse aquarium.
Numbers at top indicate 2-hour intervals startigg from midnight.
Fig. 4. Percent of the total time spent in ffeding which occurred while
the animals were submerged, awash, and exposed.
Fig.5. Activities during two spring tides. Symbols as in Fig.1.
120
.


Fig. I

Legends
Cloudy
No activity
Sun
Activity present
9
Moon (half)
Probably feeding
Denotes bright

Locomotion but
Calm surf
L
not observed
a Medium surf
On top of rock
1
Heavy surf

Jo On side of rock
2hoo o400
2000
1800
2200
0200
0600

Observation

Meteorological
o
Conditions
errerever
Surf
A -
—
Locomotion
Feeding
I1
To-
6  1o+
Position
e
18
Aoongggnraree
Degree of
00
Boodovat
Immersion

Corneoo
2
0800
In crevice
Under rock
Submerged
590
Awash
802 Out of water
1200
1600
1000
1400
1800
6

eee

geggezevees

eeeogred
aeasgerorb
tfft
are
M. Hone

Number
animal
moving
Number
Of
animals
moving
down
Top
rock
P of
rock
Cre¬
vice
Under
rock


A B
A E



Out of wate
A E
8
8 8
E
122
Se
of vater
oatl fesdin
2400
2000
0200
2200


T
e
o
Feeding
0200
1800 2200
0100
200
——— -—
o rvation
Meteorological
8
a
111 1
Conditions
mnn
Surf
Locomotion
HE
D
Feeding
Kr2D
Position
Degree of

Immersion
Howe