ABSTRAC
The crawling behavior of Lottia gigantea was
studied. Animals moved most when.8m to lm above tidal
level with a decline in movement observed by limpets at
levels below .4m SWL. Animals moved less when the
wave-induced velocities were higher. Animals adhered
less well while crawling, but even then could resist
forces nine times those exerted by the observed waves.
INTRODUCTION
Lottia gigantea inhabits rocks exposed to surf in
the intertidal zone (0.0 to 1.5m above MLLW) (Hewatt,
1937).
These animals characteristically move during high
tide and are stationary at low tide. (Hewatt, 1937.
Abbott 1956, Stimson 1976). However, the organisms are
subjected to maximal hydrodynamic forces at high tide
therefore, in this respect high tide is not an optimal
time for crawling. I wanted to examine whether these
hydrodynamic forces were great enough, relative to
Lottia's ability to adhere to the rock, to cause the
animals to restrict their crawling behavior.
MATERIAL AND METHODS
I
Observation of Crawling Behavior:
This study was conducted in the intertidal zone of
Hopkins Marine Station, Pacific Grove, California. The
study area was established on a vertical rock face
which extends twenty-meters from the shoreline in a
northwesternly direction. Two separate square grids
(3/4m by 3/4m) each composed of sixteen points, twen¬
ty-five om apart were painted onto the vertical surface
of rock using fluorescent paint. This rock is inhabi-
ted by numerous Lottia gigantea ranging in size from
3.5 cm to 7.0 cm. A wave height scale of six incre¬
ments, 50 cm apart was labeled in the area between the
sites. The lowest mark was 1.0 meter above MLLW.
Due to the exposed nature of the sites, observa¬
tions of limpet movement were conducted from the shore
with the assistance of a telescope (25x). Field re¬
cordings were made on five days (May 6, 7, 11, 16 and
17). Sixteen Lottia (eight in each site) were labeled
by painting flourescent numbers on their shells. A dot
was painted over each animal's apex so recordings would
be from a uniform location.
The distance individuals moved was determined by
periodically recording the position of each individual
on the grid. Observation was initiated two hours
before high tide and positions recorded for each indi-
vidual every 1/2 hour until two hours after high tide.
Records of position were compared from one time to the
next to calculate the net distance moved for each
individual during each particular 1/2 hour.
II Water Velocities
The water velocity in the vicinity of the experi¬
mental organisms was estimated as follows: The maximum
water velocity associated with a breaking wave is the
crest velocity. Here I assume that the crest velocity
is an estimate of the maximum velocity experienced by
Lottia. The crest velocity
u - Vogh
(Denny, 1985)
where u is velocity and h is significant wave height
trough to crest at breaking (Shore Protection Manuel).
For this calculation significant wave height was de-
termined by measuring the height of thirty successive
waves during high tide using the wave height scale on
the rock face. hg is the average of the largest 1/3
waves.
III Limpet Tenacity
Measurements of adhesive tenacity were made in the
field. Paperclips were glued to the limpet's shells
using splash zone compound (Koppers 8-788). A record¬
ing spring scale was then attached to the clip and the
limpet was pulled from the rock at a 45° angle to the
substratum. This angle was chosen because it approxi¬
mates the direction of the vector sum of the forces of
lift and drag felt by a limpet in moving water.
Tenacities were measured for twenty Lottia.
Before testing, ten were hand touched on the apex until
they were firmly clamped down. The other ten were
pulled while crawling.
IV Determinations of Lift and Drag Coefficients
Coefficients of lift (Cp) and drag (Cp) were de¬
termined in a flow tank similar to that described by
Vogel (1981). Lift and drag forces were measured for
three different Lottia shells using lift and drag
transducers. Flow speeds varied from 0.0 to 3.58 m/s
recorded values of lift, drag, and water velocity were
used to calculate C, and Cp.
D  2r
esU
and
27
espU
(Vogel, 1981)
Where Fy and Fp are the actual forces measured at
velocity u, S, is area projected laterally of the
shell, Sp is the basal area of the shell, and p is the
density of seawater.
RESULTS
In figure 1 movement in a 1/2 hour period is
compared to an individuals height above tidal level.
Lottia are most active when .8m to 1.0m above tidal
level. At the higher and lower elevation (relative to
tidal level) activity declined. The decrease in move¬
ment at the highest levels can be explained by the
organisms being outside the splash zone thus avoiding
desiccation. Limpet movement in dry regions increases
the likelihood of body fluid loss, hence possible
desiccation. In the lower regions wave interaction
appears to have significantly decreased movement.
Using hy as an indicator of average wave height
an average water velocity at the site was calculated
for each day. The square of the velocity is propor¬
tional to the force exerted on the experimental.
Lottia.
212
F =V/2 ecsu2)2 + (1/2 ec,Sgu,
(Vogel, 1981)
Figure 2 compares u to total distance moved for
all individuals for each day of observation. There is
a significant negative correlation (b = -6.3, N - 5, r'
- .97). Lottia moved less at higher water velocities,
presumably because of the hydrodynamic force exerted on
it.
The average tenacity for stationary Lottia was
1.38 x 10° N/m2 (Sp+ 2.4 x 104N/m2) while moving indi-
viduals tenacity averaged 3.9 x 10' N/m2 (SD 7.5 x 10
N/m"). Observed wave forces were compared to limpet
tenacities. The minimum observed crawling adhesion
2.82 x 10' N/me was used in the comparison.
The
maximum calculated hydrodynamic force is
F mag V1/2 egp Cpnag
u'max)2 4 (1/2 espCtmax
umax)
with Cpmax and Crax set at the maximum lift and drag
coefficients determined in flow tank (Fig. 3). max is
the largest calculated field measurement. The safety
factor is 9.0.
DISCUSSION
At least two factors appear to affect movement of
Lottia: position relative to sea water level and the
intensity of wave force.
My observations show that
Lottia prefer to move when they are .8m to 1.Om above
tidal level. The lack of activity at levels higher
than 1.bm above sea water level maybe due to the need
for Lottia to be in a water splash zone while moving
(Abbott, 1956). If they aren't, then movement is
minimal to avoid desiccation. In contrast at levels
of .5m above SWL and below where wave activity is the
greatest individuals showed significantly less move¬
ment.
Also on days where the wave force was highest
individuals had a large decrease in total movement.
Therefore animals appear to be adjusting their behaivor
in response to the wave force environment.
A difference in tenacity was observed between
moving and stationary individuals with moving indi-
viduals adhering less well.
However, even the low
tenacity exhibited by Lottia when crawling far exceeded
the forces generated by waves during my observations.
This is not surprising when one considers such
factors as fatigue which could reduce tenacity, and
increased suseptibility to dislodgement due to terri¬
torial interactions and periodic awkward positioning on
substrate formations.
It would be interesting to examine crawling again
comparing tenacity before and after high tide to see if
any reduction in adhesion occurred due to fatique.
Other future studies would be to epoxy plates across
their shells thereby increasing drag or using videotape
from a position horizontal to the Lottia and examine
behavior during wave action.
SUMMARY
Crawling behavior in Lottia gigantea is affected
by position relative to sea water level. Greatest
movement occurs while limpets are .8m to 1 m above
tidal level. Animals .4 m above MLLW and lower
(where greatest wave activity is occurring) and
levels greater than 1.5 m above MLLW (areas of
possible desiccation stress) showed limited move-
ment.
Increased wave force inhibits total movement of
Lottia during high tide.
Significant differences exist between the tena¬
cities while clamped down and crawling.
4.
A safety factor of 9.0 was determined by comparing
the minimal force of crawling vs maximal observed
forces.
ACKNOWLEDGEMENT
I would like to thank DA. Mark Denny, Tom Hahn and
Mark Shibata for their assistance during the quarter.
Especially Dr. Denny whose influence I found conducive
for good learning.
1.
12
BIBLIOGRAPHY
1. Abbott, D. (1956) Water Circulation in the Mantle
cavity of the owl limpet, Lottia gigantea, Nautlis
69, 79-87.
Denny, M.W. (1985) Wave Forces on Intertidal
Organisms: A Case Study.
Limology and
Oceanography (In Press).
Hewatt, W.G. (1937) Ecological Studies on Selected
Marine Intertidal Communities of Monterey Bay,
Shore Protection, California. The American
Midland Naturalist 18, 161-206.
Stimson, J. (1973) Territorial Behavior of the Owl
Limpet, Lottia gigantea. Ecology 54, 1020-1030.
U.S.Army Coastal Engineering (1977) Shore
Protection Manual. Washington: U.S. Government
Printing Office.
Vogel, S. (1978) Life in Moving Fluids.
Massachusetts: Willard Grant Press, 352 pp.
FIGURES LEGEND
Figure 1: Distance moved per 1/2 hours as a function
of position relative to SWL.
Figure 2:
Velocity vs Distance moved per day,
Increased velocity (proportional to force)
results in lower total distance moved.
Figure 3:
Maximum lift and drag coefficients of three
lottia shells (apex orientated at 90° to
flow) with velocity ranging from 0.0 to 3.5
m/s.
8
.6
1.O
TERRITORY POSITION-SWL (M)
1.2
1.5
20
1.O
5
1.5
2.0
TOTAL DISTANCE MOVED (M)
*

igene 3
MAX. COEFFICIENTS OF LIFT & DRAG


O
9