Temporal pattern of desiccation and
recovery in the high intertidal
limpet, Co
isellad
gitalis
Carol Marzuola
Hopkins Marine Station, Pacific Grove
June 1935
ABSTRAC
This study focused on the temporal pattern of recovery from
desiccation stress in the high intertidal limpet, Collisella
digitalis. Experiments were done on the effects of cumulative
desiccation on groups of limpets with different submergence
periods in between exposure periods. Results showed that
limpets submerged for : .5 hours between repeated desiccation
periods had an increased rate of weight loss after a series
of 5 exposures. Limpets submerged for 4 hours between stresses
exhibited weight gain during the experiment while 2 hours
of submergence resulted in no significant weight changes.
When limpets with a desiccation stress of 157 weight loss
were allowed to equilibrate with sea water, a period of 2
hours was required for osmotic equilibration of the body
fluid. More prolonged submergence of desiccated individuals
results in an overshoot of weight recovery at osmotic equili¬
bration. The data suggests that not only does recovery
time play an important role in determining the upper limits
of the intertidal distribution of C. digitalis, but may also
determine the lower limits as well.
INTRODUCTION
The high intertidal limpet, Collisella digitalis, has
often been cited for its remarkable ability to withstand long
periods of desiccation. Research done by Wolcott (1973) reveals
that this limpet can survive a loss of 80% total water when
desiccated under moderate conditions. Information such as
this is useful when comparing C. digitalis' tolerance to desic
cation with lower intertidal limpets and trying to explain
limpet zonation. However, often in the field, it is not just
one day or one short stretch of days with unusually warm weather
and/or low low tidesthat cause kills, but a series of days of
moderate stresses that accumulatively weaken the organism
(Branch, 1981). C. digitalis is certainly found in areas where
it could be subjected to these types of stresses,
With this in mind, it should be pointed out that along with
C. digitalis' remarkable ability to withstand long periods of
desiccation, it must also possess an equally remarkable ability
to recover safely and rapidly from water loss. Experiments
were designed to examine the patterns of water balance with
sets of repeated desiccation stress of 20 hours followed by
different periods of submergence for recovery. The time course
for equilibration of the osmotic concentration of the body
fluids after a desiccation stress was also evaluated. Equili-
bration was monitored for two sets of limpets, one continuously
submerged and another removed to air after .7 hours of sub¬
mergence.
Little research has been done in assessing recovery time.
but its importance is cited by several authors (Branch 1981
Davies 1969). Results from this study reveal that there seems
to be an ideal recovery time for a given total weight loss and
that longer submergence time does not necessarily result in
better recovery. Perhaps the time it takes C. digitalis and
other limpets to recover is more important in determining loca¬
tion in the high intertidal than had previously been emphasized.
MATERIALS AND METHODS
Experiment 1:
Forty limpets were collected at Still Water Cove, Monterey
County, California, and placed in separate plastic petri dishes
two days before experimenting began. During this time, all
limpets received, on average, three hours of submergence daily
to insure that none were stressed due to desiccation. The
limpets were separated into four groups of ten (Groups O. .5
2, and 4). All groups had limpets of similar sizes, ranging
from a mean radius of 9.8 mm. to 13.3 mm (Mean radius - limpet
length + width/2).
A period of exposure of 20 hours was selected to approximate
times of exposure normally found in the field when C. digitalis
is wet only by the high high tides. To simulate a desiccation
stress, experimental limpets were placed in air circulated by an
electrical fan and under lamps that maintained the temperature
at about 21°C. These conditions are not abnormal for the high
intertidal limpet and were not expected to cause any other harm
(i.e. heat stress) to the limpets.
2 -
All limpets were submerged for 4 hours before the first
period of exposure. Following this, the limpets were exposed
for 5 periods of desiccation with different submergence times,
Group .5 limpets were submerged .5 hours after each 20 hour
desiccation period. Group 2 limpets were submerged 2 hours
after each 20 hour period. Group 4 limpets were submerged
4 hours after each 20 hour period. Group O limpets were not r
submerged following the first submergence until 116 hours after
the exposure.
The limpets were submerged by placing the petri dishes
in a bath of running sea water. Following each submergence,
the dish and the limpet were blotted dry and weighed on a
Mettler balance to one hundredth of a gram. The initial
weight W(i) was the weight of the limpets following the first
submergence. During the time of exposure the limpets were
weighed periodically until the next time of submergence,
Period 5 was the last exposure period for Groups ,5, 2.
and 4. Weight loss of limpets was then followed for 60 hours,
After 116 hours of desiccation, Group 0 limpets were submerged
in water and their weight gain was measured over 24 hours.
Weight loss for each group was analyzed by taking the
fraction of weight left after a period of time, W/W(i), where
W(i) is the initial weight at time O of the first period of -
exposure. Since heat absorption and hence, evaporation rate,
is proportional to the surface area of the limpet (Branch, 1981).
W/W(i) was then normalized with respect to the total surface
area (Total surface area - Trr2 + h2 + Ir2). This method takes
into account the perimeter of the shell through which water is
3
lost (Wolcott, 1973). The method is:
) (Normalized) - Wo - aw
3/W(i)
Wo is the weight of the limpet at time O at the beginning of
each exposure period, AW is the water weight loss, S, is the
average surface area of the limpets and Si is the surface area
of a given limpet. The mean of this W/W(i) was then determined
at each time and plotted,
Since weight loss during period 1 was the same for all
groups, their rates were pooled together. Using least square
fit, the values for the slopes (rate of desiccation) for the
exponential weight loss were determined. Slopes for period 1.
pooled and by group, are given in Results.
Experiment 2:
Limpets of similar sizes were collected at Pt. Pinos.
Monterey County, California, and desiccated to 13-15% total
weight loss. At that time mantle and body water was collected
from 6 limpets to determine osmolarity. The limpets were then
submerged in a bath of running sea water for .7 hours. Body
and mantle water samples were collected again from 6 limpets.
Half of the population was then removed from water and left at
room temperature. The other half was left in the sea water,
Samples were collected periodically from both populations for
10 hours.
Mantle water was extracted by gently squeezing the foot.
Body fluid was obtained by slitting the bottom of the foot and
extracting fluid with a microhematocrit capillary tube, These
- 4 -
samples were centrifuged to settle out particulates and the
osmolarity of the supernatant was determined with a Precisions
System Microsmometer that utilizes freezing point depression.
RES
Experiment 1:
Figure 1 depicts theweight loss of Group 4 following 5
days of repeated 20 hour exposures with 4 hour submergence
time. As expected, rate of weight loss is high during the
first few hours and then begins to level out with time (Wolcott
1973). Least square fit values reveal the slope (Rate of desic¬
cation) for period 1 to equal .011f.0013 (group 4 alone) /
.0093f.001 (pooled) and the slope of period 5 to equal .Ollt.0019,
Rates of desiccation, thus, were not significantly different,
There is a significant difference between W/W(i) at time O for
each period: limpets at time O in period 5 weighed an average of
1.056:.026 x their original weight, W/W(i).
The pattern of weight loss for Group 4 is shown in Figure
2. Weight gain during their 4 hour submergence showed a gradual
increase over successive periods of exposure. Period 3 shows the
limpets gaining, on average, 1.017t.0075 x their initial weight.
Figure 3 shows that the 2 hour submergence group (Group 2)
also changed little in the rate of weight loss between periods
I and 5 (mj-.0084.0005 (group 2 alone)/.00932.001 (pooled),
m5-.0091.0012). Unlike the limpets in Group 4, these limpets
showed little fluctuations from their initial weights, W(i),
at the beginning of each period.
5 -
Limpets submerged for .5 hours/20 hours (Figure 4) showed
a significant increase in the rate of weight loss during period 5
(mj-.010f.0007 (group .5 alone)/.0093 t.001 (pooled), mg-.0174.0023).
Weight at time 0/period 5 was slightly lower than t-o /period 1:
limpets, on average, weighed .984t.013 x lower than their initial
weight, W(i).
Figure 5 compares the pooled weight loss of period 1 for
all groups, including Group 0, and the extended time of period 5
of Groups .5, 2, and 4. The rate of desiccation of Group ,5 is
clearly greater than the other groups as described above. The high
standard deviation of the mean of this group can be accounted
for by 2 limpets that had died as their time of exposure increased.
This, too, was evaluated as a sign of accumulative stress. The
rate of weight loss of period 5 of Groups 2 and 4, as discussed:
above, are not significantly different from period 1.
Group O limpets that were placed in sea water following
hours of desiccation showed increases in weight up to 1.0574.016 x
their original weight after 10 hours submergence,
Experiment 2:
Osmolarity for limpets following 13-157 total weight loss
was high as expected (1450 mOsm/1 H20). Following .7 hours of
submergence, mantle water was 970 mOsm/1 H90 (sea water) and
body water osmolarity had dropped to 1100 mOsm/ 1 H20. The
body osmolarity of the population removed from sea water staved
at around 1100 mOsm/1 H20 and the mantle water rose to 1150 mOsm/
1 H20.
The body water of the population in sea water kept dropping,
but had not reached sea water osmolarity at 1.3 hours. Body osmo¬
- 6 -
larity equilibrated with sea water between 1.3 and 2.3 hours
after submergence. After this time, body osmolarity dropped
slightly below sea water osmolarity.
DISCUSSION
It is helpful to think of the groups as occupying different
positions in the intertidal, starting with Group 4 in the lowest
position, Group 2 in the middle, and Group .5 in the highest.
Presumably as one goes higher into the intertidal, time for
recovery decreases and chances for longer periods of desiccation
increase (Davies, 1969). Above the level of the low high tide
to the neap high tide, there is not much difference in the
increased exposure time for desiccation but this study shows
there to be a great impact in the different, times of submergence
with respect to water and salt balance. In assessing recovery.
it is important to look at both the way the limpets regain weight
after a period of exposure and how theyosmotically equilibrate
after a certain weight loss. Without the full time for recovery.
one would expect a gradual increase in weight loss.
Group .5 nicely supports this prediction. If sea water
equilibration time lies somewhere between 1.3 and 2.3 hours.
than Group .5 did not have quite enough time to either equilibrate
or regain the weight lost over a series of exposures. This, in
turn, had a marked effect on the final period of prolonged expo-
sure when the rate of weight loss was significantly increased.
Although 4 hour submergence is enough time in which to
equilibrate with sea water, Group 4 appears to regain too much
weight during this time. The limpets, following repeated desic-
cations, exhibited a bloating of 1.06 x their original weight.
One author attributes this process ofswelling to a rapid intake
of water through the gut in Notoacmae scutum and suggests that
this form of uptake allows a more rapid recovery to normal
volume (Webber 1969). Possibly the bloating is due to the
high concentration difference between body osmolarity and sea
water at the time of submergence. In either case, the rapid
weight gain would seem to add a second stress. In the field.
this swelling could create a loss of tenacity on the substrate
(Boggs, 1985). Since the lower limits of C. digitalis do not
seem to fall below an intertidal height where more than 4 hours
of submergence are experienced daily, it would appear that
digitalis' lower limits are being set by this factor, a sug
gestion first made by Hoffman (1976).
The weight gain of Group 2 did not significantly rise or
fall below the initial weight. This group would have had time
to both equilibrate and regain lost water. Their rate of weight
loss did not change from one period to the next, and, unlike
Group 4, this group did not experience the excessive swelling
of Group 4. The 2 hour period of submersion would appear
close to the ideal time for these limpets following 13-157
total weight loss. In fact, a study done on another mid inter-
tidal' limpet, Patella vulgata, showed that after 1.9% water
loss, it took 1.8 hours for the species to recover water (Davies,
1969). With only a slight loss of water, these limpets took
nearly the same time to recover as the digitalis in the previous
experiments where water loss was five to ten times as great.
It is unclear whether this recovery time included osmotic
equilibration, but it certainly suggests that recovery time,
like tolerance to desiccation, must play an important role
in choosing a limpet's habitat (Branch, 1981).
One author points out that desiccation times in the lab
are generally longer than any time that is seen in the field
(Underwood, 1979). This is certainly true for the C. digitalis
tested in my lab. They survived up to 116 hours without water
and it is rare that they would be subjected to this length of
exposure in the field. During their 20 hours of exposure.
these limpets performed well. Death seemed to occur in the
limpets at about 20-257 total weight loss but the most these
limpets experienced during one 20 hour exposure was 10-157 weight
loss. However, during period 5 when the limpets were exposed
for longer than 20 hours, these limits were clearly approached
by Group .5 limpets. Following repetitive exposure with only
a minimal amount of water, the effects of cumulative stress
became evidently detrimental to these limpets.
In thinking about what could happen in nature, one could
imagine a period of time in which high intertidal limpets re-
ceived only one half hour of water daily and then suddenly re-
ceived less or no water for a period of time. Kills reported
in the field were often preceded by warm weather, or,more....
importantly, low surf, and usually involved those limpets at
the upper limits of their ranges (Wolcott, 1973). Limpets
in these cases seemed to have overestimated their tolerance to
a series of exposures. Windless weather and low surf would
provide little or no water in which to recover.
It is also possible to imagine limpets receiving no water
for a period of time and then suddenly receiving 2 to 4 hours
of submergence by either high tides or wash by waves. If the
rate of water gain is rapid and uncontrollable, than the bloating
could also become dangerous. The problems associated with des¬
iccation could entail new problems with recovery. When Group O
limpets were finally submerged following 116 hours of exposure,
none exhibited rapid and normal recovery. They swelled up to
1.05x their original weight within 4 hours and did not return
to normal weight until approximately 15-20 hours after submer-
gence. Most of the limpets seemed severely weakened; by this
I mean that none of the limpets left their petri dishes when
placed in the water, as is normal, and four out of six of them
died two days later. It appears as though simply submerging
the limpets for a long period of time after an extensive exposure
does not lead to recovery. Rather, there seems to be an ideal
time of water submergence for C. digitalis which could further
explain their ranges in the intertidal zone,
More experiments of this type are needed to support these
findings. Limpets could be stressed for longer periods of time,
Osmotic and volume equilibration with sea water also needs
further testing because of the problems associated with deter¬
mining osmolarity of viscous body fluids. However, these
observations do tend to support the idea that an interactfon
between desiccation tolerated and recovery time is important
in determining the intertidal position of C. digitalis (Branch
1981, Davies 1969). It appears that C. digitalis has developed
a unique recovery ability which not only dictates how high they
are found in the intertidal, but how low as well.
REFERENCES
Loggs, David. 1985. Submergence as osmotic stress and its role in
habitat selection in the high intertidal limpet, Collisella
digitalis. unpublished MS. on reserve at the Hopkins Marine
Station Library.
Branch, G.M. 1981. The biology of limpets: Physical factors, energy
flow, and ecological interactions. Jceanogr. Mar. Biol. Ann.
Rev. 19, 235-380.
Davies, S. 1969. Physiological ecology of Patella. Mar. Biol. Ass. U.K.
49, 291-309.
Hoffman, R.S. 1976. Intertidal distribution and movement in Collisella
strigatella. West. Soc. Malac. Ann. Rep. 9, 18.
Underwood, A.J. 1979. The ecology of intertidal gastropods. Adv. Mar.
Bio. 16, 111-210.
Nebber, H.H. 1969. Uptake of sea water into the fluid spaces of the
prosobranch gastropod, Acmaea scutum. Veliger. 12, 417-420,
Wolcott, T.G. 1973. Physiological ecology and intertidal zonation in
limpets (Acmaea): A critical look at "limiting factors". Biol.
Bull. 145, 389-422.
APPRECIATION
In preparing this study I owe many thanks to many people:
Dr. William Gilly for entrusting me with his sacred Osmometer
and spatulas, Dr. Mark Denny for the use of his computer and
his enthusiasm all along, Mr. Thomas Hahn for his help in
collecting limpets and improving my vocabulary, Mr. Peter
Thompson for his analytical abilities and high tolerance /
rapid recovery to my abuse, Charles Baxter for his suggestions
and patience and chili, and all those other spring class
whim-pets that made 175H really worth it.
FIGURES
Weight loss vs. time of period 1 and Group 4/ period 5.
W/W(i) represents the fraction of the initial weight at
any given time. Each period of weight loss follows a 4
hour submergence. (correlation coefficient, r2 (period 1) -
79, r2 (period 5) = .93).
2. Weight loss vs. time of period 1 and Group 4/periods 3 and
5, showing, the progression of weight loss over.5 exposure
periods (r(period 3) -.97).
3. Weight loss vs. time of period 1 and Group 2/period 5.
Period 5 weight loss follows a 2 hour submergence. (r2 period
5 -.97).
4.Weight loss vs. time of period 1 and Group .5/period 5.
Period 5 weight loss follows a .5 hour submergence. (r2 period
5 = .97).
5. Weight loss vs. time of period 1 and Groups .5, 2, and 4/
period 5 with extended time to show significant difference
of period 1 and Group .5/period 5.
6. Osmotic equilibration of digit
lis with sea water after
a 13-15% total weight loss. Removal of half the population
from sea water occurred at .7 hours.
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