EFFECTS OF TURBULENCE
ON THE BEHAVIOR
OF TIGRIOPUS CALIFORNICUS
CHRISTOPHER G. FOSTER
HOPKINS MARINE STATION
STANFORD UNIVERSITY
June 1977
INTRODUCTION
Tigriopus californicus (Harpacticoid, Copepoda) is the predominant
inhabitant of the tide pools in the high intertidal zone from Alaska to
Baja, California. The vertical range of Tigriopus extends from tide pools
receiving occasional splash to those inundated by the majority of high
tides. Studies on population stability of Tigriopus in varied locations
are virtually nonexistant. Igarshi (1959) mentioned periodic fluctuations
of Tigriopus japonicus population size in accordance with the tidal
periodicity, but with little quantitative evidence. Vittor (1971) work¬
ing with T. californicus stated that colonization of pools is probably
accomplished via inshore current transport of animals swept from pools
which are essentially permanently populated. But, again, he presents no
data to support his suggestions. There is no literature describing the
reactions of T. californicus to turbulence or their behavior during
periods of wave shock in the tide pools.
This project was undertaken to determine the effects of turbulence,
in the form of wave action, on T. californicus.
MATERIALS AND METHODS (MARK AND RECAPTURE)
Random populations of T. californicus were collected from tide pools
known to be washed during high tide. These animals were marked using a
neutral red solution in the following manner. A saturated solution of
neutral red in 100 ml. of seawater was prepared. 30 ml. of this saturated
solution was added to 70 ml. of fresh seawater containing the Tigriopus.
The animals were kept in this container for 4 to 6 hours and were then
Page 2
rinsed with fresh seawater and placed in fresh seawater for one day. This
method resulted in a death rate of approximately 302 with the surviving
Tigriopus appearing normal, although some were lethargic. Only animals
exhibiting normal swimming behavior were used for the experiments.
A random population of 100 dyed Tigriopus was introduced about 10
hours before high tide into each of 11 separate tide pools all of which
received wash during high tide. All pools were along the coast line of
the Monterey Peninsula. Recapture took place no later than 10 hours
after the high tide, and was accomplished by draining the tide pools
through plankton netting, refilling the pools and draining them again to
extract animals missed the first time. The refilled pools were allowed
to sit about one hour before the second draining. The number of animals
obtained from the second draining was less than half of those extracted
during the initial effort.
RESULTS (MARK AND RECAPTURE)
The mean number of animals recovered from the 11 pools was 10.4,
or 10.42 of the introduced population. (S,= 1.96, range= 0-20). Several
experiments done following the release study showed dyed T. californicus
to be less fit than undyed animals.
When equal numbers of dyed and undyed Tigriopus were put into the
lowest of a series of three artificial tide pools (Fig. 1) with a flow
rate of 40 ml. per minute for 24 hours, 168 undyed T. californicus reached
the upper pool and only 3 dyed animals. Alternately 750 dyed and undyed
individuals were placed in the upper tide pool of Figure 1. Animals were
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allowed to equilibrate for one hour before equal quantities of water
(approximately 5 liters) were poured into the pool. 195 undyed Tigriopus
remained in the pool following this "wave" while only 70 dyed animals
remained. These results indicate that the percentage of undyed T. californicus
not washed away from tide pools affected by high tides is somewhat greater
than the 10.4 per cent of dyed animals calculated from my study.
MATERIALS AND METHODS (FIELD STUDIES)
Three separate types of field studies were conducted. One set of
experiments involved the use of a single type of artificial substrate
placed in the bottom of a tide pool. This substrate was a sand-rock
mixture glued to a 48 x 8.5 mm disposable petri dish. Experiments were
run over a ten hour period including the high tide. Exchange of sub¬
strates was done every hour. Only one petri dish was present at any time.
Although the experiments were run through a high tide, no waves washed
the tide pool. The other field studies involved the use of five different
artificial substrates, also in disposable petri dishes. These substrates
included loose sand, shells, organic material, clay, small rocks and a
plain petri dish. Again, these experiments were conducted over a ten
hour period including the high tide. Every hour six new substrates were
placed in the pool and the previous set was capped and removed. During
the May 24 run no waves washed the tide pool, whereas approximately 3 hours
of wave wash occurred during the May 26 run. The third field experiment
involved the use of many identical small rock substrates simultaneously
placed in the tide pool prior to the first wave wash of the high tide.
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Several of these substrates were replaced during calm periods between
the subsequent three waves. The latter two field studies were carried
out in the tide pool shown in Figure 2, located 400 meters south of
Point Joe. In all cases the individual substrates were examined under
a dissecting microscope to determine the number of animals present.
RESULTS (FIELD STUDIES)
Results of the single substrate experiment are presented in Figure 3.
Results of the differential substrate experiment are presented in Figure 4.
No Tigriopus were found on any of the substrates of the multi-substrate
test. A 50 ml. sample taken from a crevice in the back of the pool,
however, yielded 60 animals. This sample was taken following a wave which
washed the tide pool. No Tigriopus were visible in the water column at
that time. Three separate samples from the same crevice during calm
periods much after high tides yielded only 3, 4 and 7 individuals.
MATERLALS AND METHODS (LAB STUDIES)
Laboratory turbulence studies were conducted using a rectangular
plexiglass container with glass beads as a substrate. The inside dim¬
ensions of the container were 14 x 10 x 2 cm. Approximately 100 randomly
selected Tigriopus from tide pools receiving wave wash were used for the
first three studies. Tigriopus used in the fourth experiment were
collected from a tide pool at about the 25 foot level at Pescadero Point.
Three different lighting conditions were employed: 1) two microscope
lights below the container, 2) two microscope lights above the container,
and 3) constant darkness. The light intensity produced by the two
Page 5
microscope lights was 1,600 lux. The animals were placed in the pelxiglass
container and allowed to acclimate for 40 minutes at one of the three
lightings. Turbulence was introduced in the form of 30 ml. of fresh
seawater being poured into the container from a constant height. Photo¬
graphs were taken of the animals' reaction to this turbulence using a
Nikon F-28 with the motor drive attachment. Photographs in the light
experiments were shot at 2 frames per second. The constant darkness
pictures were shot at one frame per second with lighting from a Vivitar 292
strobe.
RESULTS (LAB STUDIES)
Results of turbulence on Tigriopus lit from above are shown in
Figure 5. The lower graph shows the total number of animals found in the
water column at the indicated times. The upper graph shows the vertical
distribution of the Tigriopus in the water column delineated by the per
cent of animals located in either the upper, middle, or lowest third.
The solid line indicates the percent of animals located in the lowest
third. The dashed line indicates the number of animals in the lowest
two thirds of the water column. Results of turbulence on Tigriopus
illumninated from below are shown in Figure 6, using the same format
employed in Figure 5. Figure 7 shows the results of turbulence on animals
in darkness. Results of turbulence on animals collected from the high
pool at Pescadero Point are shown in Figure 8.
DISCUSSION
The results of the mark and recapture studies indicate that
Page 6
T. californicus have some mechanism enabling them to remain in tide pools
subjected to extreme wave action. This mechanism involves leaving the
water column and relocating in a crack or crevice while the wave is
washing the tide pool. The onset of such behavior could be produced by
one of two things. The first is that T. californicus posses an endogenous
rhythm which is in synchrony with the tidal rhythm. This rhythm would
dictate the percentage of time a given individual spends in the water
column. This percentage would drop drastically concurrent with the onset
of high tide. Thus, during any period of high tide few animals would be
located in the water column and many more clinging in small cracks or
crevices. The second hypothesis is that the mechanism is triggered by
a wave entering the tide pool. This assumes that the immediate reaction
to turbulence is for the animal to leave the water column and thus heighten
its chances of survival. The number of animals located on the artificial
substrates is taken to be a constant fraction of the total number of
animals in the water column at any given time. This assumes that there
are two separate places a Tigriopus may be located: 1) in the water column,
including the substrate or 2) not in the water column, clinging in small
crevices. The single substrate experiment shows no significant decrease
in the number of Tigriopus in the water column during high tides. This
random distribution during two periods of high tide, but no wave wash,
argues against any sort of endogenous rhythm governing the animals behavior.
The results of the differential substrate tests again argue against any
endogenous rhythm synchronous with tidal activity. The study conducted
during a period of high tide only, shows no marked decrease of animals
Page 7
in the water column. The data points fall as random fluctuations about a
mean. The May 26 experiment, however, clearly points out a drastic reduction
of animals in the water column during wave wash. This indicates that
turbulence, or wave action itself, is necessary to stimulate the Tigriopus
to leave the water column. The May 26 study shows where the Tigriopus
are not located, but does not tell one where they moved. The results of
the multi-substrate test, though, offers evidence of where the Tigriopus
are located. Although no animals were seen or retrieved from the water
column, 60 were collected from the back crevice. This is almost ten times
more animals than were collected by three separate samples during calm
periods. This suggests that the onset of waves signals the Tigriopus
to accumulate in the crevice to avoid being washed out of the pool.
The question which now arises is what component of the turbulence
response leads them to that, or any other crevice. Tom Glaser (personal
communication) noted a strong negative phototaxis in response to turbulence.
Figure 8, though, shows that animals lit from below dive in response to
turbulence, in fact the greatest decrese in animals in the water column
with the onset of turbulence is noted with those lit from below. This
suggests a positive geotaxis being produced by the turbulence. With no
light cues (Fig. 9) the animals were again seen to dive, and remove them¬
selves from the water column. This is more evidence toward a positive
geotaxis being produced by turbulence. The study with the animals from
the high pool (Fig. 8) shows that animals that are very rarely subject
to wave action still show the above mentioned turbulence responses. All
animals run in light were also seen to leave the upper third of the water
Page 8
column within two seconds of the turbulence. The number in the bottom
third rose and then fell as if the animals were simply passing through
it to leave the water column. No animals were located in the top third
during the darkness experiment so this decrease was not seen.
SUMMARY
Tigriopus do not have an endogenous rhythm synchronous with the
tidal cycle which regulates the time when they leave the water column.
Their survival behavior to wave action is keyed by the actual turbulence
and involves a positive geotaxis.
Page 9
AKNOWLEDGEMEN
I wish to thank Dr. Robin Burnett for his invaluable assistance
and constant zaniness throughout this project. Special thanks also
to the other members of the Burnett Lab for extended good times and
to Tom Glaser for help with photography. Last but not least I am
greatly indebted to Chuckles Lateef. HERMAN.
Page 10
LITERATURE CITED
Igarshi, S.
1959. On the relationship between the environmental conditions
of tide pool and the Tigriopus population. Bulletin of the
Marine Biological Station of Asamushi. 9,4: 167-171.
Vittor, B.A.
1971. Effects of the environment on fitness-related life
history characters in Tigriopus californicus. Ph. D. Thesis,
University of Oregon.
0
Figure 1. Photograph of artificial tide pools.
1
FIGURE
Figure 2. Photograph of study site for second
and third field experiments. 400 meters
south of Point Joe.
FIGURE 2
Figure 3.
Graph of single substrate experiment.
Number of animals on substrate vs.
time of day.
10
NUMBER
ANIMALS
ON
SUBSTRATE 6
4
2
HIGH TIDE
5/19
20
119

5/20

2400 0200
1300 2000
2200
9400
0100 0300 0500
2300
1900 2100
TIME OF DAY
FIGURE 3
Figure 4. Graph of differential substrate experiment.
Number of animals on substrate vs. time of day.
78

0


I

2
C

T.
—2
2
o


FIGURE 4
Z
2


I
0
Figure 5. Graph of reaction to turpulence
of animals illuminated from above.
1o0
%
ANIMALS
50
NUMBEF
INIMAL
WATEF
M
30
20-
10
UPPER-

-
MIDDLE

OW
TURBULENCE
TIME
8
B
Figure 6. Graph of reaction to turbulence
of animals illuminated from below.
100-
%
OF
ANIMALS
60-
50-
VUMBER
NIMALS
VATER
LOLUM
20
10-
UPPER

MIDDLE
o
LOW

A
TURBULENCE
D
E
B
TIME
Figure 7. Graph of reaction to turbulence
of animals in darkness.
100—  8BEEE—
MIDDLE
r
ANIMAL
Q

50
LOW
40
NUMBER
O
ANIMALS
WATER 20
COLUMN

10-
TURBULENCE
2 TIME
PPER
—
C
Figure 8. Graph of reaction to turbulence
of animals from the high pool when
lit from above.
100-
INIMALS
50-
50-
NUMBEF
ANIMALS
WATER
COLUMN
20-
10
UPPER

MIDDLE

o
LOW
TURBULENCE
TIME
0
2

3