Chapter 8: Animal Populations in Relation to Wave Action in the Subtidal Region of
Zonation Rock
or
Splendiferous Subtidal Superstars
Isabella Dorfman & Noah Rossen
2013 Chapter 8 pg.1
Chapter 8: Animal Populations in Relation to Wave Action in the Subtidal Region of
Zonation Rock
We counted the animals on each side of Z-rock off the coast of Racing beach, Falmouth, MA to determine whether
wave action had an effect on the population. We hypothesized that greater wave action would correlate with a lower
population. We found that the sides of Z-rock with more intense wave action have higher populations of U.cinerea
and Anachis, and the sides with less intense wave action had higher populations of L. littorea, though the amount of
L. littorea was insignificant. In conflict with the findings on Z-rock, X-rock had a much larger population of
U.cinerea and Anachis on the protected shore side and populations on the west side were very low in comparison.
We found no L. littorea on X-rock. The organisms on X-rock experience much more intense wave action than those
on Z-rock, possibly explaining these conflicting findings. This information is crucial considering the precarious
state of the intertidal ecosystem on many parts of the Cape, which is undergoing increased human interference and
rising sea levels.
Introduction
Z-rock is the ideal location for a thorough investigation into intertidal life, as each of its
four sides are subject to different degrees of weather. The north and west sides take the most
wave action and sunlight while the South and East sides are relatively protected. The results
should give us a clear indication of the effect of wave action on the population of various
creatures. We hypothesize that the side of Z-rock with the most intense wave action will have the
smallest population of creatures because of the harsher environment.
We conducted our experiment in the low intertidal and subtidal zones of Z-rock. The mid
intertidal zone is usually submerged except at the low tides twice a day. Thick algae cover large
portions of this zone. L. littorea inhabit this zone only when it is above water. The low intertidal
zone, right beneath the mid intertidal zone, is also only exposed twice daily at low spring tides.
The subtidal zone is constantly submerged and is host to a number of vertebrates and well as
U.cinerea and Anachis
L. littorea mainly inhabit the upper spray zone, though they do appear in the mid and low
intertidal at low tide. As the tide rises, L. littorea crawl back up to drier zones. They live off a
diet of seaweeds, microorganisms and other detritus. U. cinerea mainly inhabit the lower
intertidal and subtidal zones and feast on a variety of small oysters and shellfish. The genus
Anachis inhabits all zonations.1 2 3
1.
1
"Life in the Intertidal Zone." Life in the Intertidal Zone. N.p., n.d. Web. 04 June 2013
2013 Chapter 8 pg.2
The Intermediate Disturbance Hypothesis states that areas with an intermediate amount
of disturbance have increased species diversity, whereas areas with intense or weak disturbance
are less diverse. This hypothesis states that moderate upheaval to the ecosystem is necessary for
the continuing functioning of diversity. With no disturbance the ecosystem would settle,
uprooting the species that thrive on opportunity and change. Species that compete for space and
resources would become dominant. Moderate disturbance allows for a balance. High disturbance
would be too intense for some species to handle. The harsh environment would not be beneficial
for a diverse population because most species would die or be forced out. An intermediate level
of disturbance allows for a more diverse ecosystem with enough disturbance to keep things
changing without harming the animals.4
While only examining the populations of a single seemingly insignificant rock, our study
helps explain the stresses that might affect these organisms. This information is crucial
considering the precarious state of the intertidal ecosystem on many parts of the Cape, which is
undergoing increased human interference and rising sea levels. This study also examines a new
region of Z-rock, being the lower intertidal and subtidal areas. These areas have not previously
been studied.5
Materials and Methods
For our study we used an Atlantic seashore: a field guide to sponges, jellyfish, sea
urchins, and more identification book, two wetsuits, a waterproof notebook, pencils, plastic
sample bags, goggles, snorkels, a meter stick, a microscope, pipettes, glass and plastic slides, a
point and shoot camera, and 15 X 15cm duct tape quadrat.
Start on the left of the eastside of Z-rock at low-tide. Place the quadrat above the
waterline and count the number of organisms in the quadrant, taking note of species. Record
Fucus coverage. Move the quadrat down two full squares and repeat until the quadrat reaches the
2.
3
4
2
"Tidal Zones." Welcome to Where the Land Meets the Sea! N.p., n.d. Web. 04 June 2013.
"Intertidal Zonation." Intertidal Zonation. N.p., n.d. Web. 04 June 2013
4.
http://academic.research.microsoft.com/Paper/5046872.aspx
5
5.
Below:, To Learn More about Research and Monitoring Efforts Taking Place at Cape Cod National
Seashore Visit the Pages Linked. National Parks Service. National Parks Service, 04 June 2013. Web. 04 June 2013.
2013 Chapter 8 pg.3
base of Z-rock. On the lower intertidal, we measured from 30 cm above the waterline to the
water line. In subtidal , we measured from the water line to -30 cm. In subtidal 2, we measured
from -30 to -60 cm. In subtidal 3, we measured from -60 to -90 cm. Place quadrat to the right of
the first quadrat and repeat procedure until all of the rock has been examined on all sides. Record
daily wave action on all sides of rock. These steps should be repeated on the West and Shore
sides of X-rock, which is located about 30 feet southwest of Z-rock. For X-rock, only examine
the intertidal zone, as the subtidal zone is too harsh to get an accurate count.
Because of frigid water temperatures, poor visibility, and wetsuit buoyancy, we altered
our method. Instead of placing quadrats, we counted the populations in four horizontal strips,
starting quadrat about the waterline at low-tide to the base of the rock.
2013 Chapter 8 pg.4
Results
Total Individuals On Z-rock
160
140
Total Number
120
100
80
Combined Species
60
40
20
0
West
Shore
South
North
Figure 1a: The West side of Z-rock has the most (141) total individuals, the Shore/ East
side has the second most (79), the North side has the third most (75), and the south has
the least (37). A chi test shows that the total individuals are distributed amongst the
sides significantly different than expected. (P-value: 1.88379E-14)
Wave Height Avg.
12
Total Height (cm)
10
8
6
Wave Action Avg.
4
2
0
West
Shore
South
North
Figure 1b: The West side of Z-rock had the highest (12cm) wave height avg., the South and
North side had the second highest (8cm), while the shore side had the lowest (5cm).
2013 Chapter 8 pg.5
Wave Highpoint Fluctuation
80
Total Height (cm)
70
60
50
Day 1
40
Day 2
30
Day 3
20
10
0
West
Shore
South
North
Figures 2a and 2b: The South and the North had the highest high point and highest low
point, the west had the second highest high and low points, and the shore side had the
lowest high and low points. Figures 2a and 2b reflect each other. There are no clear
outliers in the data over the three days. Figure 2a and 2b support the accuracy of
Figure 1b.
Wave Lowpoint Fluctuation
80
Total Height (cm)
70
60
50
Day 1
40
Day 2
30
Day 3
20
10
0
West
Shore
South
North
2013 Chapter 8 pg.6
Species Pop. on Z Rock
160
140
120
Total Number
100
Littorina
80
Oyster Drills
Anachis
60
40
20
0
West
Shore
South
North
Figure 3: The West side of Z-rock has the most Oyster Drills (107), the most
Anachis (34), and is tied for the fewest Littorina (0). The North side has the second
most Oyster Drills (48), the third most Anachis (21) and the most Littorina (6). The
Shore side has the third most Oyster Drills (47), the second most Anachis (27) and
the second most Littorina (5). The South side has the fewest Oyster Drills (18) and
Anachis (19) and is tied for the fewest Littorina (0).
2013 Chapter 8 pg.7
Lower Intertidal (30 cm)-(waterline)
50
Total Number
40
30
Littorina
Oyster Drills
20
Anachis
10
0
West
Shore
South
North
Figure 4a: The West side of Z-rock had the most (46) Oyster Drills, the second
fewest (10) Anachis, and had no Littorina. The North side had the second most
(21) Oyster Drills, the least(8) Anachis, and the second most (2) Littorina. The
Shore side had the third most (16) Oyster Drills, The most (24) Anchis and the
most (5) Littorina. The South had the fewest (10) Oyster Drills, the second most
(14) Anachis and no Littorina.
Total Number
Subtidal 1:(waterline)-(-30cm)
50
45
40
35
30
25
20
15
10
5
0
Littorina
Oyster Drills
Anachis
West
Shore
South
North
Figure 4b: The West side of Z-rock has the most (28) Oyster Drills, the most
(19) Anachis, and no Littorina. The Shore side has the second most (19) Oyster
Drills, the fewest (2) Anachis and no Littorina. The North side has the third
most (13) Oyster Drills, the second most (8) Anachis, and (4) Littorina. The
South side has the fewest (7) Oyster Drills, the third most (3) Anachis, and no
Littorina.
2013 Chapter 8 pg.8
Total Number
Subtidal 2:(-30cm)-(-60cm)
50
45
40
35
30
25
20
15
10
5
0
Littorina
Oyster Drills
Anachis
West
Shore
South
North
Figure 4c: The West side of Z-rock has the most (24) Oyster Drills, and the most
(5) Anachis. The Shore side had the second most (11) Oyster Drills. The North
side had the third most (6) Oyster Drills. The South side had the second most (2)
Anachis. No Littorina were present.
Subtidal 3:(-60cm)-(-90cm)
50
45
Total Number
40
35
30
Littorina
25
Oyster Drills
20
Anachis
15
10
5
0
West
Shore
South
North
Figure 4d:The West side of Z-rock has the most (9) Oyster Drills. The North side
has the second most (8) Oyster Drills, and the most (4) Anachis .The Shore side is
tied for the fewes (1)t Oyster Drills, and has the second most (1) Anachis.
TheSouth side is tied for the fewest (1) Oyster Drills. There were no Littorina.
2013 Chapter 8 pg.9
Wave Action
12
Total Height (cm)
10
8
6
Wave Action
4
2
0
West
Shore
South
North
The South and North sides of X-rock had the highest (6cm) wave
height, while the West and Shore side has the lowest (3cm) wave height.
X-Rock
60
Total Number
50
40
Littorina
30
Oyster Drills
20
Anachis
10
0
West
Shore
The Shore side of X-rock had the most (57) Oyster Drills, and the most
(41) Anachis, while the West side had the fewest (7) Oyster Drills, and
the fewest (5) Anachis. There were no Littorina present. The shore side
is more diverse (Shannon Diversity Index: Shore=1.017, West=0.9393).
2013 Chapter 8 pg.10
.8<p<1= significant
p<.05=significant
west shore south
north
west shore south north
chi test
CORRELATION
observed
141
total individuals
expected
83
observed
littorina
expected
observed
oyster d
expected
observed
anachis
expected
Observed
x rock species
expected
observed
x rock Oyster d
expected
observed
x rock anachis
expected
0
79
37
83
83
5
0
75
mean wave ht
1.8838E-14 vs
83
total species
12
5
8
8
141
79
37
75
mean wave ht
vs
2.0959E-16 littorina
12
5
8
8
0
5
0
6
mean wave ht
vs
oyster d
12
5
8
8
107
47
18
48
12
5
8
8
34
27
19
21
0.658
6
0.01078227
2.75 2.75
107
55
34
47
55
27
2.75 2.75
18
55
19
48
-0.643
55
21
0.721
0.14375977
25.25 25.25
12
98
55
55
7
57
25.25 25.25
mean wave ht
vs
anachis
0.511
2.40831E-16
shannon diversity index
4.10453E-10
32
32
5
41
23
23
1.10889E-07
west shore
observed
153 177
x rock + z rock total specied w and s
0.186449181
expected
165 165
z rock total =
1.063
x rock total =
1.018
z rock west =
z rock shore =
z rock south =
z rock north =
1.263
0.963
0.973
0.975
x rock shore =
x rock west =
1.017
0.939
2013 Chapter 8 pg.11
Chi tests proved that the observed distribution of the total individuals, Littorina, and
Oyster Drills, along the four sides of Z-rock, was statistically significant compared to the
expected distribution. This was not true of the Chi test for the Anachis on the four sides of Zrock, whose distribution was statistically insignificant, compared to the expected distribution.
The Chi tests performed for the total individuals, Littorina and Anachis, on the two sides of Xrock were statistically significant. This shows that the observed distribution of these species
along the sides of X-rock were statistically significant compared to the expected distribution.
However, when we combined the total individuals on the two sides of X-rock to the total
individuals on the two corresponding sides of Z-rock, a Chi test proved that the observed
distribution was not statistically significant compared to the expected distribution.
The Correlation Coefficient tests compared wave action on the four sides of Z-rock to the
distribution of individuals amongst those sides. All of the tests did not show statistical
significance in the wave action effecting the distribution of individuals on the sides of Z-rock.
The Littorina, Anachis, and cinerea were not affected by the wave action on their side of Z-rock.
We used the Shannon Diversity Index to compare different areas to determine which side
was the most diverse. Z-rock’s West side was the most diverse, followed by the North side, and
ending in decreasing diversity with the South side and the Shore side. For X-rock, the Shore side
was more diverse than the West side. When compared, Z-rock proved to have slightly greater
species diversity than X-rock.
Conclusion
The data was either not significant or not thorough enough to prove or disprove our
hypothesis. We hypothesized that the sides of Z-rock with more intense wave action would be
less populous due to the harsh environment, while the sides with less intense wave action would
be more populous. We found that the sides of Z-rock with the most intense wave action had
higher populations of L. littorea, U. cinerea, and Anachis, contrary to our hypothesis. We
overestimated the strength of the wave action on these sides of Z-rock, which in reality only
experienced intermediate levels of disturbance. In the 2008, Jetty Animal Diversity (ScrimshawHall and Holman, 2008) the researchers hypothesized that the North side, which had an
intermediate level of disturbance (in this case, an average wave height of 10.25 is considered an
2013 Chapter 8 pg.12
intermediate level), would prove the most diverse, while the intense western and calm southern
sides would be less diverse.
We conducted our study in particularly calm weather. The West side of Z-rock, which
was the most populous and diverse, had the most intense wave action at 12 cm. While 12 cm
waves seemed high for us, it is considered an intermediate amount of disturbance, explaining the
increased population. Despite the different highs and lows, our findings agree with those of
Scrimshaw-Hall and Holman. A study of Animals on the rocks (Green and Domond, 2007), also
explains our results. Their data showed that the side of the jetty with intermediate (12cm) wave
height disturbance was more diverse than other more intense or less intense parts of the jetty.
Our data charts show the distribution of the species along the intertidal and subtidal
regions of Z-rock and the corresponding wave action. It also shows the results from X-rock,
which we compared with the results from Z-rock. Figure 1a and 1b show the West side of Zrock, which has an intermediate amount of disturbance, has the highest population and diversity
(Shannon diversity index: 1.263). The Shore side has the next largest population, closely
followed by the North side, which did not correlate to less intense wave action, as the North and
South sides had more intense wave action than the Shore side. Despite the varied population
sizes, the species diversity was similar for all three sides (Shannon Diversity Index:
Shore=.9631, South=.973, and North=.9751). We believe that the West side accurately
represents species diversity and the Intermediate Disturbance Hypothesis, while the low
disturbance may negatively affect the other sides’ population and diversity. Figure 2a and 2b
show the fluctuation of the high and low point of the wave height across three days of
measurements and that there was not one significant outlier that threw off the data. It proves that
the data in figure 1b accurately represents wave height on each side of Z-rock. This shows that
the data we collected on species populations accurately represents the effect of waves action of
the population. Figure 3 further explains figure 1a. It shows the total population of different
species on Z-rock and which side of the rock they inhabit. It shows there was generally more U.
cinerea on each side of the rock then there were Anachis or L. littorea. It shows, because of
intermediate disturbance, that the west side has the most U. cinerea and Anachis, while all the
other sides have lower populations of both species. This chart also shows that we only found L.
littorea on the shore and North side of Z-rock. We believe the harsher waters on the west side
discouraged the habitation of L. littorea , as they prefer drier areas (see figure 4a, 4b, 4c, and 4d).
2013 Chapter 8 pg.13
We cannot explain the absence of L. littorea on the south side of Z-rock. Figures 4a, 4b, 4c, and
4d show the distribution of individuals amongst the different depth of Z-rock. Figure 4a shows
that the lower intertidal row of Z-rock is the most populous. This chart shows the populations of
all 3 species. The populations decrease in Figure 4b, the first subtidal region, though do not
disappear completely. In the Figures 4c and 4d, we see an extreme drop in the population of
species, and an understandable absence of L. littorea in both subtidal rows. In all 4 charts, the
North and West sides of Z-rock have higher populations. We believe that the North side of the
rock, despite having the same wave height as the South side, may have a higher population,
because it is being hit more directly by the tide. We observed that the tide seemed to flowed
North to South, which creating more disturbance on the North side of the rock. Figure 5a and 5b
shows the data collected from X-rock. We collected this data in the same fashion as on Z rock,
but only recording the West and Shore sides, as it does not have north and south sides. These
charts show that there was a different pattern to the wave action. The wave action was highest on
the South and North sides, and lower on the West and Shore sides. When compared to Figure 1b,
the wave height is generally lower on X-rock than on Z-rock. The Z-rock wave action numbers
are more accurate than those of X-rock, as we recorded three days worth of wave height for the
former and only one day worth for the latter. Figure 5b shows a very large population on the
Shore side, while few animals reside on the harsher West side. We noticed many of the species
on the West side hid in or very near the Fucus. We believe that these species use the Fucus as
protection against the waves. It is worth noting that the different shape of X-rock making any
comparison the Z-rock moot. X-rock is much smaller and almost entirely subtidal, while Zrock’s tall shape rises well above the water at low tide. X-rock’s West side is almost parallel to
the sky with the shore side almost perpendicular to the sky, allowing the waves to crash over it.
Water disturbs X-rock very differently than it disturbs Z-rock, as waves merely slosh along the
rock at the water line. On X-rock, we counted the species in the intertidal zone but not the
subtidal zone. We unsurprisingly observed a complete absence of L. littorea on X-rock, as Xrock is too wet and harsh an environment for L. littorea to survive.
Our study contained various flaws. Since we worked by touch, we most likely
undercounted and misidentified the population. We estimated the size of each level and may
have attributed a certain number of animals to the wrong level. We made two separate attempts
on the South side count and our first try may have displaced the creatures, influencing the count
2013 Chapter 8 pg.14
on our second and official try. We suggest next years group study other similar rocks and the tip
of the jetty in addition to Z-rock and X-rock. Since the two rocks yielded such different results, it
would be interesting to see what other areas tell. We did not investigate Fucus coverage on Zrock, which likely influences population. We suggest that a better system to define the rows or
quadrats. The much more accurate quadrat would be easier to use and place with thinner, sturdier
borders, letting a single person to hold the quadrat. We strongly suggest future groups continue
this study, as the sea level along the cape rises each year changing the size of each species’
habitat.
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2013 Chapter 8 pg.16