THE INTERACTIONS BETWEEN THE TIDEPOOL AS AN
ORGANISM AND TWO COTTID SPECIES CLINOCOTTUS
ANALIS AND OLIGOCOTTUS SNYDERI
Kelly E. Jensen
Biology 175H
June 9, 1989
ABSTRACT
This study describes the tidepool environment along the
shore of Hopkins Marine Station of Stanford University and relates
it to the population and distribution of the cottid species
Clinocottus analis and Oligocottus snyderi . The relationship
between the cottid mass per tidepool volume and the percent of
oxygen consumed by cottids in a tidepool is approximated by the
equation: 202-0.0023* (mass/vol) 60/ where oxygen is expressed
in grams, but algae seems to be the primary consumer of oxygen.
It is suggested that a potential problem for fish is having algae in
the same tidepool as a means of protection and as a competing
oxygen consumer. In addition, tidepool height, volume and range
in temperature are discussed as they relate to the cottid
population.
INTRODUCTION
Tidepool ecology is especially interesting due to the great
fluctuations in tidepool environmental factors during the course of
à tide. Every time a tidepool is separated from the ocean, it is
subject to changes in temperature, oxygen levels, salinity, pH, and
the affects of different organisms that entered it during the
previous high tide. In addition, tidepools generally have a rich
diversity of species related to their small area, a situation that
could lead to potential competition for any of a number of
resources: oxygen, nutrients, food sources, space, and light. This
study raises the question; what role do these physical factors play
in determining the species composition and abundance in
tidepools?
The family cottidae (sculpins) was chosen as the subject of
this study because of the abundance of these fish in the tidepool
and nearshore areas of the California coast (Bolin, 1944 and
Eshmeyer, 1983). This study is designed to describe the cottid
population and the tidepool environment along the coast of
Hopkins Marine Station and to use this description to illustrate a
number of factors that might be affecting where cottids live. The
investigation focuses its attention on specific tidepool parameters
that provide possible explanations for the cottid distribution, and
these explanations are presented with the idea that tidepools and
cottids are two interacting organisms.
MATERIALS AND METHODS
The study site at Hopkins Marine Station of Stanford
University (36 38' N,121 56' W) consisted of fifteen tidepools
which were chosen based on the following characteristics: complete
isolation from the ocean at low tide, difference in gross
morphology, and the ease with which an investigator could
measure the physical characteristics of the pool.
The heights of the pools in relation to mean low low water
were measured using a transit.
Tidepool surface areas were
estimated by dividing the top of the pools into rough polygons and
calculating the sum of the areas of these polygons. Volumes were
measured by bailing part of the pools and siphoning the rest of the
water. A marked bucket and a 500 milliliter graduated cylinder
were used to record the amount of water actually removed from
the tidepools, and the volume of any residual was visually
estimated. The water removed was immediately replaced with
fresh water.
Carbon dioxide was bubbled through the pools for fifteen to
twenty seconds to stun fish, which were then collected with
dipnets. Fish were taken into the lab for length, mass and species
determination and, in most cases, were immediately released into
the tidepool in which they were captured. Fish from three
tidepools were kept in the lab so that a recruitment study could be
conducted.
Recruitment was measured in two tidepools. Each was
emptied of cottids when initially censused (May 12, 1989 and May
15, 1989), and subsequent habitation was followed daily and
continued through June 1. 1989. A daily lowtide census was taken
for each pool by capturing fishes with a dipnet, measuring their
length, and determining their species. To reduce the amount of
disturbance, fish were returned to the tidepools immediately
following the census, and no carbon dioxide was used to
anesthetize the fish. The lengths of the fish were converted to
mass by using the empirically determined regression of the log of
cottid length (cm) to the log of cottid mass (grams): LENGTH -
0.0098 * MASS3.10 (R2 - 0.962, p « 0.001), calculated from the
length and mass of each cottid found in the fifteen tidepools
originally censused. The total biomass of fish found at each census
was calculated by adding the single cottid masses.
Physical data were taken for six of the fifteen tidepools;
readings were taken at low, mid, and high tides over a period of
two days (May 1, 1989 to May 3, 1989). Dissolved oxygen and
temperature were measured with a YSI meter (model 54), pH was
measured with a Markson digital pH meter (model 90), and
sälinity was determined by a Wescor 5500 vapor pressure
osmometer. The mean level for each of these parameters was
calculated from the readings taken when the pools were not
inundated with fresh seawater.
Possible relationships between the different parameters for
the tidepools were determined using a linear regression technique.
Single regressions were done to examine the correlation between
two parameters independently from the remaining parameters; a
correlation was considered significant when the R value was
significant at the 0.05 level. The SPSS multiple regression
program was used to determine the independent variables which
most significantly affect one dependent variable. Variables
included: volume, surface area, height, mean oxygen level, mean
temperature, mean phl, mean salinity, number of cottid per pool.
mass of cottid per pool, mean length of cottid per pool, and the
mass of fish/pool volume. One multiple regression was calculated
with number of fish per tidepool as the dependent variable, and
the other with cottid mass per pool volume as the dependent
variable. The relative importance of the independent variables
was determined by examination of the significance of the T test in
the regression output; only variables which produced a significance
greater than or equal to 0.05 were considered in the equation.
The rate of oxygen consumption by the representative
organisms in a tidepool was determined experimentally. 59.54
grams of C analis were placed in a fourteen-liter tank of
sand-filtered seawater. Oxygen readings were taken at intervals of
thirty minutes for four and a half hours. The rate of oxygen
depletion in grams per hour was determined by the following
calculation:
1.umles/liter0.5733timeu 541 r-
0.984). The slope of this regression (-0.5733
umoles/ liter/hour) is the rate of total consumption.
2. umoles,/liters/hr 32 ug/umoles' 1 g/10ug
10° liters/m m of tank -g0 consumed/hour
3. For a given cottid biomass: go, consumed/hour/g
cottid.
The percent of oxygen consumed by cottids in an actual
tidepool was calculated as follows:
1. g 0, consumed/hour/g cottid' g cottid in pool
time interval between readings - g 0, consumed
by cottids.
2. difference between initial and final oxygen
readings umoles/liter * 32 ug/umole * 1 g/10° ug
10°liters/m2 * m2 of tidepool - total g0 consumed
in tide pool.
3. g 0 consumed by cottid/g 0» consumed in
tidepool' 100 - percent of 0, consumed by cottids.
In order to eliminate the complicated effects of
photosynthesis on oxygen consumption, oxygen readings taken at
the beginning and end of one night (3:24pm May 3, 1989 and
4.30am May 4, 1989) were used in the calculations above to
détermine the amount of oxygen consumed by cottids in six
tidepools.
A similar experimental design was used to determine the
oxygen consumption of invertebrates and algae in one of the six
tidepools used in the cottid experiment. The experimental
biomasses were 642.6 grams of invertebrates and 333.1 grams of
algae (Appendix 1). Two, twenty-liter tanks were used, and
readings were taken every three hours for a twelve hour period.
The regression equations for oxygen consumption were
02lumoles/liter - 7.22-0.48333'timehours (R2 - 0.896, p « 0.05)
for invertebrates, and 102lumoles/liter - 8.42-0.495'timepours
(Ré- 0.882, p - 0.05) for algae.
Further oxygen readings were taken in two pools every
hour for a seven hour period on a sunny day. Two readings per
pool were used to calculate the rate of oxygen consumption in
the pools and the percent of oxygen consumed by cottids during
the day as opposed to during the night.
RESULTS
SECTION ONE: THE POPULATION
Table 1 briefly describes tidepools in which fish were and
were not found. Two species of cottid were found in this study;
Clinocottus analis and Oligocottus snyderi (Figure 1). Of the
sixty-nine fish captured, 904 were C analis (Figure 2). Six of the
seven O. snyderi were found in the same tidepool; this tidepool
contained no C. analis
Figure 3 shows the mean lengths of the total cottid
population and of each species separately. The mean lengths do
not differ significantly (p»0.05), but C analis has a much greater
range (1.8-11.7 cm) than O. snyderi (2.6-5.1 cm). The middle
70 of the total population of cottid. C. analis, and Q snyderi fall
in about the same range (3.1-5.1 cm).
The mean mass does not differ significantly (p»»0.05)
between species (Figure 4). The range in mass for C analis is
again much greater than O snyderi and the range in mass for the
middle 70% of O. snyderi (0.5-1.3 g) falls in the lower part of the
range for the middle 702 of C. analis (0.4-1.8 g).
All of the single linear regressions for tidepool parameters
were calculated to determine any independent correlations
between parameters. Many were not significant, but two show
significant correlations. Mean cottid length per tidepool tends to
increase with tidepool volume (Figure 5). The total number of
cottid per tidepool tends to decrease with the height of the
tidepool (Figure 6).
SECTION TWO: PHYSICAL FACTORS
The results of the two multiple regressions calculated are
summarized in Table 2. Mean oxygen level seems to be the most
important variable affecting both the cottid mass/pool volume
and the number of cottids per tidepool, but it appears to be more
closely correlated to mass/pool volume. Figure 7 illustrates the
independent relationship between the mean oxygen level and the
mass of fish/volume of a tidepool.
In Figure 8, the percent of oxygen consumed by cottids in
six tidepools is shown in relation to the cottid mass / pool volume
of those pools. This relationship is approximated by the equation:
« 02 - 0.0023 * MASS/VOLI.47 (r2 - 0.987. p « 0.001) where
oxygen is expressed in grams. The values for cottid oxygen
consumption during the day are also shown in Figure 8. Although
it appears that cottids consume less oxygen during the day, this
difference is probably due to the effects of photosynthesis on
oxygen levels.
The relative amounts of oxygen consumed by sculpins,
invertebrates, and algae during the night in one pool is shown in
Table 3. Algae were apparently the primary consumers of
oxygen; the oxygen consumed by algae was calculated to be
112.74, but this error may be due to the fact that the time points
for the calculation were from two low tides, and the tidepool was
replenished with fresh water and oxygen between those points.
The difference in overall consumption when algae is respiring in
the observed pool is probably still quite large.
SECTION THREE: RECRUITMENT STUDY
The change in total cottid biomass for one pool at daily
intervals over a fifteen day period is shown in Figure 9.
DISCUSSION
This study has attempted to illustrate the enormous scope
of physical and morphological characteristics of tidepools that
could affect the distribution of tidepool sculpins. Although
interaction among different organisms has been discussed in
many contexts in the past, the ways in which tidepool fishes
interact with tidepools as organisms is not well documented.
There are at least two possible scenarios to explain the
relationship that cottids have with the levels of oxygen in a
tidepool. Because the correlation between the fish mass/volume
ratio and the mean oxygen level of a tidepool is negative, a larger
amount of fish in a tidepool corresponds to a lower mean level of
oxygen. This suggests that cottids might be causing the changes in
the amount of oxygen. Alternatively, other organisms in the pool
might be more important in determining the fluctuations in
oxygen level, and this level could be a limiting factor for the fish.
This study shows that as the mass of fish in a tidepool (per pool
volume) increases, the percent of oxygen consumed by fish also
increases. But the fraction of total oxygen consumed by fish is
small and algae appears to be the primary consumer of oxygen in
a tidepool. Thus, I hypothesize that if there is causality in this
correlation, the number of fish are responding to the level of
oxygen rather than causing any change in it.
Although the most stressful time for tidepool fishes in
terms of oxygen availability is probably during the night between
high tides, because algae are respiring and the pools are not
receiving fresh water, it is difficult to state in the context of this
study whether oxygen is the limiting factor for the amount of fish
biomass that occurs in a certain tidepool. Regardless of the fact
that algae and invertebrates use much more of the total oxygen
overnight than cottids, oxygen levels in the tidepools where
these fish reside might never drop to dangerous levels before
they are replenished with fresh sea water or sunlight for
photosynthesis. Further experimental studies are needed to
settle this question.
In the observed tidepool, algae is apparently the primary
oxygen consumer by quite a large margin. If oxygen is in fact a
significant limiting factor, then an interesting situation occurs,
Algae provide an advantage for the fish as a means of protection
from predators, but it also might provide a disadvantage by using
large amounts of oxygen and possibly leaving the cottid with a
less than ideal oxygen level.
The above calculations for oxygen consumption in the
observed tidepool were made using the fish biomass / pool volume
of the unmanipulated pool. This biomass was equal to was the
initial level of this pool while it was used in the recruitment
study. Over the course of this study, biomass reached a
maximum of almost exactly this level before dropping again and
remaining quite low. (Figure 9). This information poses the
question of whether there exists a maximum for cottid biomass in
tidepools in relation to the amount of oxygen available to the fish.
Determining whether different cottid species consume oxygen at
significantly different rates and investigating the occurance of
these species in tidepools with varying amounts of algae would
be useful to answer this question. Further areas of investigation
might include what, if any, mechanism the fish have to detect
such a limit and whether fish are distributed accordingly,
Other correlations between different tidepool parameters
suggest possibilities for explaining the distribution of tidepool
fishes. For example, the positive correlation between tidepool
volume and mean cottid length might be another possible
illustration of the distribution of cottids according to some
limiting factor. Cottid length is related to biomass by the
equation LENGTH - 0.0098 * MASS 3.10. This regression includes
only those pools which contain cottid, which tended to be richer
in algae and invertebrate diversity than those without fish (Table
1). In similar pools, the bigger the pool the more resources it
contains. It follows that larger fish could reside in larger pools.
Included in this explanation of where tidepool fishes occur
is the question of where they do not occur in the intertidal zone,
The negative correlation between tidepool height and number of
13
cottids illustrates that there are tidepools that are probably
difficult for cottids to reach physically. Those pools which only
get splashed occasionally due to their distance from the ocean are
not only difficult to encounter, but may also have characteristics
which are detrimental to tidepool fishes. For instance, one
tidepool in the study area (which contained no fish) receives
fresh seawater only at the highest tides when a large wave sends
water through a small channel to the pool. Not only is the salinity
of this pool higher than that of regular seawater, but algae
growth is poor and the diversity of other organisms is relatively
limited.
Finally, the two species of cottid found in this census did
not reside in the same tidepools. In the context of competition
among similar species, this might suggest that, instead of sharing
the resources in the same tidepool by using them at different
times or by using separate resources (Yoshiyama 1977), these
fishes are simply not residing in the same space. Another
possibility, however, is that the environment affects these species
in different ways. According to Nakamura (1976), O. snyderi
have a lower tolerance of wide temperature extremes than other
cottid species. The fact that the six of the seven Q. snyderi found
in this study area were residing in a tidepool that was almost
always receiving fresh ocean water and had the smallest
temperature range over a tide cycle supports the possibility that
14
the fishes prefer to stay in such a pool.
Because it is generally agreed that there is no single
environmental factor that causes a certain distribution of
intertidal fishes, this study has attempted to record the different
characteristics of tidepools and examine those characteristics that
appeared most important in determining where cottids were
found. The scenarios presented to explain the distribution of
cottids along the rocky intertidal zone of Hopkins Marine Station
were developed with a specific idea in mind: that tidepools might
be usefully observed as interactive organisms as well as
environments.
LITERATURE CITED
Bolin, Rolf L. 1944. Cottid and Myctophid Fishes of California. Natural
History Museum of Stanford University. 3: 67-70, 73-76.
Eschmeyer, William N. Earl S. Herald, Howard Hammann.1983. A Field
Guide to Pacific Coast Fishes of North America. Boston: Houghton
Mifflin Company. pp. 161-185.
Morris, Robert M. 1960. Temperature, salinity, and southern limits of
three species of pacific cottid fishes. Limnology and Oceanography
5: 175-179.
Morris, Robert M. 1961. Distribution and temperature sensitivity of some
eastern pacific cottid fishes. Physiological Zoology, 34: 217-227.
Nakamura, Royden. 1976. Temperature and vertical distribution of two
tidepool fishes. Copeia. 1976: 143-152.
Toshivama, Ronald Masaru. 1977. Competition and Rocky Intertidal Fishes.
PhD thesis University of Michigan. Ann Arbor: Xerox University
Microfilms.
APPENDIX 1: INVERTEBRATES AND ALGAE USED IN OXYGEN
CONSUMPTION EXPERIMENT
INVERTEBRATES 642.6 grams
2 Pachygrapsus crassipes
Stongylocentrotus purpuratus
2 Patiria miniata
38 Tegula funebralis
9 Pagunis samuelis
1 limpet (unknown species
1 Heptacarpus pictus
1 pelagic crustacean
ALGAE 333.1 grams
Pelvetia fastigiata
Gigartina caniliculata
Corallina pinnatifolia
Corallina vancouveriensis
Prionitis cornea
Endocladia muricata
Mastocarpus jardenii
TABLE I. GENERAL TIDEPOOL DESCRIPTIONS
DESCRIPTION
roeoos
TIDEPOOLS
OF Po
WITHNO COTTIO
WITH COTTID
DIVERSITYO
INVERTEBRATES
HIGH
LOW
GRDWTH OE
POOR
RICH
ALGAE
2 1.807m
HEIGUTS
21.682m
MEAN
SALINITY
1050.25 mo/
2070.83 mol/
TABLE 2.
MULTIPLE REGRESSION OUTPUTS
DEPENDENT INDEPENDENT
8
SLOPE
VARIABLES
VARIABLE
-2.85
0.758
NOMBER
MEAN,
OE COTTID
LEVEL
TEMPERATURE 11.24
0.227
-71.44
0.410
MEAN
2. MASS/VOL
RATIO
LEVEL
SICNIFICANCE
ooouc
oouae
o.o021
TABLE 3.
OXYGEN CONSUMPTION IN ONE TIDEPOOL (NIGAT)
ORGANISM
6RAMS O, CONSUMED
%O, CONSUMEO
COTTIOS
2.24
0.452
INVERTEBRATES
637.2
1.144
ALGAE
1589.0
100
FIGURE LEGENDS
Figure 1. Clinocottus analis and Oligocottus snyderi. Bolin, 1944.
pp.125 and 127.
Figure 2. Species of sample population.
Figure 3. Length description of sample cottid population. The range
in lengths for the overall cottid population. C. analis and Q. snyderi
are shown by a bar graph, and the mean lengths for each catagory are
represented with a horizontal line. The shaded portion represents the
middle 704 of each population. The value 702 was chosen because
the Osnyderi population is composed of only seven fish; one fish was
removed from the upper and lower limits.
Figure 4. Mass description of sample cottid population. The upper
and lower limits for the O snyderi population were removed to shoy
the middle 702 of the population (shaded area) and this value was
used in the other populations also.
Figure 5. Tidepool volume versus mean cottid length. The regression
equation and its significance is shown.
Figure 6. Tidepool height versus number of cottid. The regression
equation and its significance is shown.
Figure 7. Mean oxygen level versus cottid mass/volume.
Figure 8. Cottid biomass per pool volume versus 2 oxygen consumed
by cottid. The circles represent oxygen consumed at night, and the
squares represent consumption during the day . The equation of the
curve is approximated by: LENGTH - 0.0023 * MASS/VOL 1.47 (R2 -
0.987, p «0.001) where 0» is expressed in grams.
Figure 9. Cottid recruitment. The initial level represents the amount
of cottid mass found in the initial census of the tidepool studied.
FIGDRE 1.
CLINOCOTTUS ANALIS AND OLIGOCOTTUS SNYDERI










2







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Clinocottus analis (Girard). Q Drau by Rolf L. Bolin.



4

11


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...
Oligocoltus snyderi Creeley. Q Draun by Walter B. Schwarz.
FIGURE 2.
SPECIES OE SAMPLE COTTID POPULATION
00
60
2 20


COTTIO C.ANALIS O. SNYOERI
EIGURE 3.
LENGTH DESCRIPTION OF SAMPLE COTTID POPULATION
10% 01
SAMPLE POPULATION
COTTIO C.ANALIS O. SNYDERI
FIGURE 4.
MASS DESCRIPTION OF SAMPLE COTTID POPULATION
107 0r
SAMPLE POPULATION

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