Abstract
Wave exposure is a complex set of biotic and abiotic factors, including
variations in physical force, light, temperature, and nutrient levels. This study
examines the distribution and morphology of an intertidal rockweed, Pelvetia
compressa (Fucales, Phaeophyta) at three sites along a wave exposure gradient
on the Monterey Peninsula, California, USA. Percent cover and vertical ranges
were similar between the most exposed and intermediately exposed sites and
much greater than at the most protected site. A discriminant function analysis of
morphological data shows that the three populations may be objectively
classified into three groups based on morphology. Äfter a discriminant function
analysis, it is possible to accurately predict the site of origination for most of the
thalli examined. Patterns between the morphological data from the extremes of
wave exposure suggest that plants at the most exposed location tend to break at
lower internodes, producing a "leggy" and pruned morphology compared to
those at the protected site. This pruning may serve to lower drag forces and
hence be an adaptation to heavy wave exposure. It is unclear from the data
what factors are responsible for patterns seen at the intermediate exposure site;
differences in age structure or other demographic factors may play an important
role.
Introduction
Wave exposure is an important factor in the ecology of the rocky intertidal
shore. It consists of a complex set of biotic and abiotic factors (Cousens 1982)
and plays an important role in structuring intertidal communities (Dayton 1971.
Sousa 1985). In addition to its effects on entire communities, wave exposure
often influences the zonation of individual species along the intertidal shore
(Stephenson and Stephenson 1949, Carefoot 1977, Ricketts et al. 1985). Öther
effects on individual species include changes in growth rate (Cousens 1982) and
changes in morphology (Denny et al. 1985, Gaylord et al. 1994, Blanchette
1994, Cousens 1982). In addition, material strengths of algal thalli may increase
in high energy environments (Kraemer and Chapman 1991). Such changes
reflect adaptations to stresses associated with wave exposure.
In this study, I asked: Does the morphology, material strength, and
distribution of Pelvetia compressa, a common intertidal alga, vary at three sites
along a wave exposure gradient in a quantifiable, statistically significant way?!
measured several characteristics of Pelvetia thalli at these three sites, including
length, holdfast dimensions, internode dimensions, and material strength. also
quantified percent cover, density, and vertical ranges of Pelvetia at each
location. Secondly, I asked, if morphology, material strength, or distribution does
vary at each site, can any of this variability be an adaptation to wave exposure?
Materials and Methods
Study Sites
Ihree sites were chosen along a wave exposure gradient on the Monterey
Peninsula in Pacific Grove, California, USA (Fig. 1). The most protected site was
at Hopkins Marine Station (hereafter HMS) located on Point Cabrillo. The study
site faces north and is protected from waves by several off-shore rock
formations. The intertidal zone is horizontally broad and gently sloped. It also
includes many medium to large boulder clumps, creating small "islands."
Morphology data was taken immediately to the west of Agassiz Beach while the
distribution was measured over a 30m by 120 m area of the intertidal.
The intermediately exposed site was on the west side of Lovers Point
(hereafter LVR). It is very narrow with many steep, almost vertical faces and the
north/northwest facing study site is approximately 30 m long. The most exposed
site was on the north face of Point Pinos, (hereafter PTP). It is a very broad and
gently sloped rocky shore several hundred meters long. The gradient was
established using off-shore wave heights taken near the Monterey Bay Aquarium
(Monterey Bay Aquarium, unpublished data), located near the study site at HMS,
as well as by regression formulae which predict wave heights near the other two
study sites (Graham 1995).
All measurements were made in months of April and May, 1996.
The Study Organism-Pelvetia compressa
Pelvetia compressa (C. Ag., De Toni), formerly known as Pelvetia
fastigiata (J. Agardh, De Toni, De Cew and Silva in press) is a brown, perennial
intertidal alga, commonly found either isolated or in thick aggregations on top of
protected rocks in the mid-littoral belt from Coos Bay, Oregon to Lower California
(Ensenada) (Setchell and Gardner 1925). In the areas studied, Pelvetia
compressa is the only species of this genus; it will hereafter be referred to as
Pelvetia. The fronds branch closely above an ellipsoid holdfast in a dichotomous
fashion with apical growth (Lee 1980) but Pelvetia also is morphologically plastic.
Multiple apical cells may be initiated at sites of damage, so Pelvetia may appear
to branch in a non-dichotomous fashion. Pelvetia produces gametes yearly in
bloated reproductive structures called receptacles at the tips of ultimate
dichotomies and shed their gametes at low tide (Bold and Wynne 1978). Like all
fucoids, Pelvetia has only a diploid macroscopic phase and lacks alternation of
generations. Since the holdfasts of adjacent Pelvetia may fuse, one
morphological individual may represent not one but many genetic individuals.
Therefore, following the convention of Aberg (1989) a morphologically distinct
individual will be labeled a "plant" or "thallus" and not "individual". I define
"morphologically distinct" as an plant whose holdfast does not contact that of any
other. All plants in this study were reproductively mature and randomly selected
from the middle of the Pelvetia zone.
Distribution and Vertical Range Measurements
1o establish the vertical range of Pelvetia, I used a surveyor's transit and
stadia rod. Heights were measured relative to a USGS benchmark (at HMS) or
relative to the predicted height of the water at low tide (PTP and LVR).
To measure percent cover at HMS, I sampled random points within the
vertical range of Pelvetia inside a 120 m by 30 m transect. Using a 0.25 m-
quadrat, I counted the percent cover and number of individuals inside each
quadrat. At LVR, 0.25 m2 quardrats were placed randomly within two transects,
one 30m by 2 m and the other 23 m by 2 m. At PTP, three 30 m by 2 m
transects were sampled. The percent cover and densities were compared with a
one-way ANÖVA followed by a Tukey's test to determine significance of
differences between sites. The ANÖVA calculations for density measurement
were performed upon log,, transformed data due to heterogeneity of variances.
Morphology
The following features of Pelvetia were measured for thalli at each site
(figure 2): maximum frond length (to nearest centimeter), number of stipes per
holdfast, and holdfast and stalk cross sectional area (to nearest 0.01 mm). For a
randomly selected frond in each thallus, the following features were measured:
internode lengths (to 0.01 mm) and areas (to 0.01 cm2) for lowest 3 internodes
breaking strength of the frond (Nem2), and location of first non-dichotomous
branching (hereafter referred to as "bushiness"). Twenty-five plants were
measured at HMS, 22 at LVR, and 24 at PTP.
Distinctness of the morphologies at the three sites was determined using
discriminant analysis. The discriminant function analysis is a multivariate
statistical technique which creates linear combinations of the morphology
variables to maximize differences among the study sites. Next it applies this
discriminant function to individual observations to classify whether a plant came
from HMS, LVR, or PTP. If the morphologies are different at the three sites, the
discriminant function should correctly classify each plant. If they are similar, the
discriminate function will not classify them correctly. In addition, the separation
of the three populations may be graphically displayed as an xy-scatter plot. The
x-axis (Factor 1) represents a combination of morphological variables which
maximizes differences among the sites. The y-axis (Factor 2) is a second
combination of morphological variables with the second largest difference among
sites but is also statistically independent from factor 1 (Afifi and Clark 1984).
In addition, single factor ANÖVA's were performed on the morphological
features individually to test for differences among sites. Those which were
significantly different were tested with a Tukey's tests to find significant
differences between sites.
In addition, ten plants from each site were haphazardly removed from the
site to analyze thallus areas and lengths using the computer program NIH Image
1.55 (National Center for Supercomputing Applications). Each thallus was
spread upon a sheet of paper and videotaped. The image was imported into
NIH Image and traced to find the area.
Strength as a Material Property
lo find the strength of the thallus as a material property, the breaking
strengths of approximately 100 plants from each site were measured using a 20
kg spring scale and nylon webbing to hold each frond. The webbing was
wrapped around the end of each frond and attached to the spring scale. The
scale was then pulled until the frond broke cleanly. The cross sectional area of
each break was found by measuring the dimensions of each break and the
breaking strengths were computed as:
=Breaking Force (Newtons))/(Cross Sectional Area of Break (m2))
These strengths were ranked in numerical order and each rank was given
a probability of:
probability - rank
n+1
with n= total number of plants at each site. These probabilities were graphed
versus their associated breaking strengths to show the probability of breakage
for a plant at each site given a certain breaking strength. The mean strengths
from each site were tested with a one-way ANÖVA followed by a Tukey's test to
test differences between means.
Results
Distribution and Vertical Height
The vertical range of Pelvetia was similar at LVR and PTP. At both
these sites, Pelvetia extends both higher and lower in the intertidal height range
than at HMS (Table 1).
LVR and PTP also had similar percent covers and density; at both sites,
density and percent cover were greater than at HMS (Fig 3). ANOVA
calculations indicated significant differences (p « 0.05) among the three sites
(Table 2 & 3). A Tukey's tests showed significant differences of density and
percent cover (p « 0.05) between all pairwise combinations of sites except
between LVR and PTP.
Morphology
Compared to HMS plants, the plants at PTP appear tougher and "leggier.
The first several internodes are longer and most branching does not begin until
the 4th or 5th internode at PTP. These long internodes often have scars where
a branch had been broken off. Plants at LVR, however, appear to have much
new growth with very regular branching.
-Discriminant Function Analysis
The discriminant function correctly classified most of the plants from each
site (Table 4). The individual features which were significantly different (p «
0.05) among the sites were internode lengths, internode areas, bushiness, and
breaking strength (Table 5). In general, internode length increases from HMS to
LVR to PTP while internode areas are similar at HMS and PTP but less at LVR.
PTP plants begin to "bush" at lower internodes than those at HMS and LVR (Fig.
4). These features would create plants with thin internodes at LVR and plants
with long internodes at PTP. These results confirm qualitative observations
about the plants at each site. The separation of the three populations based
upon morphology may be illustrated as an xy-scatter plot (Fig. 5).
PIP plants had a lower ratio of plant area to length than those at HMS
(Table 6). At-test between HMS and PTP showed a significant difference
between the mean ratios of area to length at the 95% confidence interval.
-Breaking Strength as a Material Property
The cumulative probability of breakage versus breaking strength curve
illustrates that LVR plants are noticeably weaker than those at HMS and PTP
(Fig. 6). The PTP plants have the strongest material of all three sites. In
addition, a one way ANÖVA on the mean breaking strengths showed significant
differences (p « 0.05) among the three sites (Table 7). All pairwise differences in
means were significant by a Tukey's test (p«0.05)
Discussion
Pelvetia Distribution
The differences in vertical range of Pelvetia among the three sites is not
unexpected. Intertidal zones shift upwards along the shore and broaden when
exposure increases (Lewis 1964, Ricketts et al. 1985, Carefoot 1977). In
addition, the range found for Pelvetia at HMS agrees with that found by Doty in
1946 who studied intertidal zonation at HMS (Doty 1946).
It was unexpected that HMS would have such a low percent cover and
density compared to LVR and PTP since Pelvetia has been reported as a
protected intertidal species (Setchell and Gardner 1925). This pattern, however,
may still be related to the degree of protection of a shore. Cousens (1982)
describes exposed locations as "less extreme and less variable" (p. 194) due to
temperature and nutrient buffers created by greater water turnover. It has been
shown that the abundance of other fucoids varies through time with
environmental conditions, usually due to desiccation stress (Gunnill 1980). In
addition, it has been noted that the Pelvetia population at HMS has declined
sharply in the last 20 years (Watanabe, Baxter personal communication). It is
possible that desiccation stress at HMS may have killed a large percentage of
the population and that such environmentally-dependent variability may be an
important factor in Pelvetia's ecology. The lower wave exposure at HMS,
therefore, may have contributed to a decrease in abundance through desiccation
stress. Percent cover and density at LVR and PTP may be similar for several
reasons. The actual wave exposure at these two sites may be very similar or
there may be a threshold wave exposure which allows Pelvetia to reach a
maximal abundance, after which its abundance becomes limited by other factors
such as competition for space.
Morphology
The discriminant function analysis showed that the three populations are
morphologically distinguishable since most plants were accurately classified. In
addition, single factor ANÖVA's showed that several morphological features as
well as breaking strengths varied significantly among the sites. Since these
three populations are statistically distinguishable, I hypothesized that there may
be biological reasons for this separation.
To elucidate the biological reasons behind the morphological differences,
first examined differences between HMS and PTP, the two sites at the extremes
of wave exposure and asked if the variability in morphology and breaking
strength could be adaptations to wave exposure. There were no significant
differences in internode area between these two sites so the plants do not grow
thicker fronds at PTP to adapt to wave exposure. Plants at PTP are stronger
than those at HMS; for a given breaking strength, PTP plants are less likely to
break than those at HMS. Changes in algal material properties as a response to
wave exposure have also been studied in Egregia menziesii (Kraemer and
Chapman 1991); the strengths of young Egregia thalli were greater when grown
in high energy situations than those grown in low energy situations. Increasing
the material strength of the algal tissue, therefore, may be one adaptation of PTF
plants to wave exposure.
Another feature which significantly differs between HMS and PTP is
internode length. There could be several explanations why internode lengths at
PTP are approximately twice those at HMS. First, the internodes could grow to
longer lengths at PTP and branch less. Second, the plants at PTP could prune
and break off branches due to wave forces, making a longer internode out of two
or more shorter internodes. The second explanation may be more likely
because l observed many long internodes at PTP which were actually the result
of two shorter internodes separated by a scar where a branch had been broken
off. In addition, pruning could be an adaptation to wave forces. The drag force
is proportional to the amount of area on an object. It is possible that Pelvetia
adapts to wave forces by reducing area on which drag may act while maintaining
the same internode thickness. This adaptive characteristic has been seen in
other fucoids (Blanchette 1994) and mechanical limits to size due to wave forces
have been postulated for other intertidal algae (Gaylord et al. 1994). Pruning
may reduce the area on a thallus and hence reduce the amount of drag if the
plants did not regain the pruned area by growing more at the tips of the thalli. If
the plants do lose area at PTP relative to those at HMS by pruning, the ratjo of
area to length should be less at PTP than at HMS. This is true (Table 6); hence.
the differences in internode lengths between the two sites may be related to
pruning as an adaptation to wave forces. Though the reduction of area per
length from HMS to PTP seems fairly small, this amount may be enough to
significantly reduce the drag forces on plants at PTP (see Appendix 1).
Cousens (1982) found that the morphology of Ascophyllum nodosum at
an intermediately exposed site was not necessarily intermediate compared to
sites at the extremes of exposure. Many morphological features at LVR are not
intermediate compared to those at HMS and PTP. Internode lengths are
intermediate compared to those at HMS and PTP; this result agrees with the
pruning hypothesis. If the plants prune as an adaptation to wave forces and the
wave forces are intermediate at LVR compared to HMS and PTP, then the plants
at LVR should prune an intermediate number of times. The average internode
length should be between those of HMS and PTP.
Internode areas at LVR were less than those at HMS and PTP (Fig. 4b)
and breaking strengths were much less (Fig. 6, Table 7). These results are
difficult to understand in terms of wave forces. If wave forces are greater at LVR
than at HMS, why would the thalli at LVR grow weaker and thinner than those at
HMS? There could be several explanations for the patterns at LVR. Öther
factors of wave exposure, such as temperature or nutrient levels, specific to the
amount of exposure at LVR may contribute to these patterns. The nutrient levels
may allow for more new growth at LVR, creating thinner and weaker internodes,
In addition, there may be other causes which are unrelated to exposure. The
reason for the morphologies at LVR may be specific to the population at LVR¬
perhaps the plants are of a different age structure or different gene pool. The
results do not clearly suggest one possibility over another; further study should
be conducted on the population at LVR to determine what factors control the
morphologies and breaking strengths.
In conclusion, this study showed that the distribution, abundance, and
morphology of Pelvetia are distinct at these three sites along a wave exposure
gradient and that some of these differences may be adaptations to wave
exposure. The factors contributing to the distinct features of LVR plants remain
unclear. When conducting an ecological study of wave exposure, one must
remember that exposure consists of many factors whose relative influence may
change at different exposure levels (Cousens 1982). Most commonly associated
with wave exposure are mechanical factors (Denny et al. 1985, Denny 1988) or
wave-borne projectiles (Shanks and Wright 1986). In addition, there are
biological factors associated with water motion such as decreased desiccation
stress or temperature and nutrient levels. At a very exposed location,
hydrodynamic forces create a very extreme mechanical environment while
temperature and nutrient buffers due to increased water turnover create a less
extreme environment (Cousens 1982). The ultimate impact upon the ecology of
intertidal organisms is due to a combined effect of these factors. In addition.
without conducting long-term demographic studies or reciprocal transplant
experiments, one cannot disregard demographic factors or site-specific
characteristics in a study of exposure and morphology/distribution. Age
structures of the populations at each site may be different, causing widespread
differences in morphology. Since the growth rates of Pelvetia may be negative
(Gunnill 1979), it is difficult to ascertain growth rates and ages. An age structure
could only be determined by following plants over a number of years. One way
to determine if the environment is responsible for the morphological variability in
Pelvetia would be to perform reciprocal transplant experiments between
protected and exposed sites. Such an experiment has been conducted on
Fucus gardneri (Blanchette 1994); the results supports the hypothesis that wave
forces directly influence plant morphology. A reciprocal transplant experiment
should be done with Pelvetia in conjunction with a discriminant function analysis
This would show whether transplanted thalli from site "a" looked more like those
at site "a" or those at the site of transplantation, site "b" after a certain amount of
time. If the discriminant function classifies thalli transplanted from site "a" to site
"b" as site "b" plants, it would further strengthen the claim that wave exposure
strongly influences the morphology of Pelvetia.
Acknowledgments
Tam indebted to Dr. James Watanabe for his assistance with the
discriminant function analysis and with the experimental design, as well as for his
endless patience and good-humor. In addition, I thank Dr. Mark Denny for his
frequent and lucid explanations of biomechanics and wave forces. The following
people have also been instrumental in my research: Dr. J. Wible, B. Gaylord, Dr.
C. Blanchette, Dr. J. Connor, Dr. P. Silva, Dr. S. Brawley, S. J. Liaw, J.
Strharsky, E. Leydig, and C. Patton.
Literature Cited
Aberg, P. (1989). Distinguishing between genetic individuals in Ascophyllum
nodosum populations on the Swedish west coast. Br. Phycol. J. 24: 183-
190.
Afifi, A. A. and V. Clark. (1984). Computer Aided Multivariate Analysis.
Belmont, California: Lifetime Learning Publications.
Agardh, C. (1924). Systema Algarum. vol. 38. Lunda: Literis Berlingianis.
Agardh, J. (1841). In historiam algarum symbolae. Linnaea. 15: 1-50.
Bell, E. C., and M.W. Denny. (1994). Quantifying "wave exposure": a simple
device for recording maximum velocity and results of its use at several
field sites. J. Exp. Mar. Bio. Ecol. 181: 9-29.
Blanchette, C. A. (1994). The effects of biomechanical and ecological factors on
population and community structure of wave-exposed, intertidal
macroalgae. Oregon State University.
Bold, H. C. and M. J. Wynne. (1978). Introduction to the algae. Englewood
Cliffs, New Jersey: Prentice-Hall, Inc.
Carefoot, T. (1977). Pacific seashores: A guide to intertidal ecology. Seattle:
University of Washington Press.
Cousens, R. (1982). The Effect of Exposure to Wave Action on the Morphology
and Pigmentation of Ascophyllum nodosum (L.) Le Jolis in South-Eastern
Canada. Botanica mar. 25: 191-195.
Dayton, P. K. (1971). Competition, disturbance, and community organization:
the provision and subsequent utilization of space in a rocky intertidal
community. Ecol Monogr. 41: 351-389.
De Cew, T. and P. Silva. (in press).
De Toni, J. B. (1895). Sylloge Algarum. vol 3. pp. 215-216. Patavii:
Sumptibus auctoris.
Denny, M. (1995). Predicting physical disturbance: mechanistic approaches to
the study of survivorship on wave-swept shores. Ecol. Monogr. 65(4):
371-418.
Denny, M. W., et al. (1985). Mechanical limits to size in wave-swept organisms.
Ecol. Monogr. 55: 69-102.
Denny, M.W. (1988). Biology and the mechanics of the wave-swept
environment. Princeton: Princeton University Press.
Doty, M. S. (1946). Critical tide factors that are correlated with the vertical
distribution of marine algae and other organisms along the Pacific coast.
Ecology. 27: 315-328.
Gaylord, B., C. A. Blanchette, and M.W. Denny (1994). Mechanical
consequences of size in wave-swept algae. Ecol. Monogr. 64: 287-313.
Graham, M. (1995). Regulation of the shallow limit of giant kelp, Macrocystis
pyrifera, at three sites along the Monterey Peninsula. San Jose State
University.
Gunnill, F. C. (1979). The effect of host distribution on the faunas inhabiting an
intertidal alga. DAI. 40: 4012-4444.
Gunnill, F. C. (1980). Demography of the intertidal brown alga Pelvetia
fastigiata in Southern California, USA. Mar Biol. 59: 169-179.
Kraemer, G. P. and D. J. Chapman. (1991). Biomechanics and alginic acid
composition during hydrodynamic adaptation by Egregia menziesii
(Phaeophyta) juveniles. J. Phycol. 27 (1): 47-53.
Lee, R. E. (1980). Phycology. Cambridge: Cambridge University Press.
Lewis, J.R. (1964). The ecology of rocky shores. London: Hodder &
Stoughton.
Longuet-Higgins, M. S. (1952) On the statistical distribution of the heights of
sea waves. J. Mar. Res. 11: 245-266.
Ricketts, E. F. et al. (1985) Between Pacific Tides. Stanford: Stanford
University Press.
Setchell, W. A. and N. L. Gardner. (1925). The marine algae of the Pacific coast
of North America. Berkeley: University of California Press.
Shanks, A. L., and W. G. Wright. (1986). Ädding teeth to wave action: the
destructive effects of wave-borne rocks on intertidal organisms.
Oecologia. 69: 420-428.
Sousa, W.P. (1984). Disturbance and patch dynamics on rocky intertidal shores.
In The ecology of natural disturbance and patch dynamics, (ed. S. T. A.
Pickett and P. S. White), pp101-124. New York: Academic Press.
Stephenson, T.A., and A. Stephenson. (1949). The universal features of
zonation between tide-marks on rocky coasts. J. Ecol., 37: 289-305.
Appendix 1. Determination of maximum wave heights and drag force
Hydrodynamic forces on a wave-swept shore consist of lift, drag, and
acceleration. The lift force acts perpendicular to the direction of flow and is
proportional to area. Drag is also proportional to area but acts in the direction of
flow. Acceleration also acts in the direction of flow but is proportional to an
object's volume. The effects of lift and acceleration are usually small in relation
to drag (Denny 1995, Gaylord et al. 1994) which is why only drag is considered
in these calculations. The relative exposure of the three study sites was
determined by visual estimation of wave height and offshore wave heights at
each location as determined from wave height data and regression formulae
(Monterey Bay Aquarium, unpublished results, Graham 1995). To estimate
relative wave forces at the three sites lused these off-shore wave heights.
Extrapolating from off-shore wave heights to degrees of in-shore exposure,
however, is very complex and involves making empirical measurements of
topography at each site (Denny 1995). In addition, local variations in topography
might make exposure highly variable on a scale of meters within the same site
(Bell and Denny 1994).
Taking the average maximum significant wave height at the Monterey Bay
Aquarium from 1987-1992 as the maximum significant wave height at HMS,
applied this value to a Graham's (1995) regression formula to find the maximum
height at PTP. From this maximum wave height, I found the am..
d-H (1)
272
ams is not the standard deviation of surface elevation but only the root-mean¬
square of the amplitude of waves. Using the statistics of extremes (Longuet¬
Higgins 1952),I found the maximum wave amplitude:
dmax - (n(f 1)
Ddms (2) (Longuet-Higgins 1952)
2I()
with f=1/9 s" (Denny 1995), 0 = .5772, and t = 8 hours since the measurements
made for the off-shore wave heights at the Monterey Bay Aquarium were taken
every 8 hours.
The maximum wave velocity for a turbulent bore running up the beach is:
(3)
Imax — 8 (20ma)
with una= maximum water velocity and g= 9.81 m:s2. For PTP, the maximum
wave velocity was 9.55 m.s" while at HMS, the maximum wave velocity was 7.22
m.s.
The maximum drag force was calculated as:
Fa =3puPSpAp (4) (Denny 1995)
with p=density of seawater, 1024 kg-m“, Sap =the shape coefficient which is a
constant for each organism at a particular orientation to flow = 0.18 (Gaylord,
personal communication), ßy is the velocity coefficient = 1.7 (Gaylord, personal
communication), and Ap, is the maximum projected area
A PTP plant with an average length per area of 0.319. m’/m and an
average length of 0.368 m would experience a drag force of 501.4 N. If it had
the same average length per area as HMS plants (.4199 m2/m), it would
experience of a force of 660.0 N. An average length plant at HMS (0.396 m)
would experience 441.5 N. Without the reduction in area per length, a PTP plant
experiences 1.49 times the drag force as a plant at HMS. Äfter the reduction in
area per length, the PTP plant experiences only 1.14 times the drag force as a
plant at HMS
Tables
Table 1. Heights of Pelvetia (feet above MLLW)
Site
Lower Limit Upper Limit
Range
(ft above
(ft above
(ft above
MLLW
MLLW
MLLW
HMS
4.15
3.09
1.06
4.00
LVR
5.62
1.62
PTP
1.94
5.9
3.96
Table 2. Analysis of variance of percent cover of Pelvetia at HMS, LVR, and
PTP
Source of Variation of
MS
value
4111.87 6.86 0.002
Between Groups
Within Groups
111
599.015
Total
113
Table 3. Analysis of variance of density of Pelvetia at HMS, LVR, and PTP.
Due to heterogeneity of variances as determined by the Cochran’s test, the
ANÖVA calculations were performed upon log,, transformed data.
Source of
P-value
MS
Variation
Between Groups
1.86
9.92 60.001
111
Within Groups
0.19
113
Total
Table 4. Predicted sites of origination based upon morphological characteristics.
The elements in each row originated at the same site; these elements are placed
in columns which are the predicted sites of origination.
Site
Predicted
Total
PI
LVR
HMS
Actual
18
HMS
21
LVR
18
21
PTF
20
21
Total
23
Table 5. Single factor ANÖVA calculations on morphology data
VARIABLE
DE
MS
Length
110340
2.525
089
Error
60
43.703
Stipes/Holdfast
35.244
1.938
153
60
Error
18.185
Internode 1 Length
1056.866
6.003
004
60
Error
176.048
Internode 1 Area
1047.565
3.258
045
Error
60
321.566
2086.457
9.500
Internode 2 Length
0.000
60
Error
219.636
Internode 2 Area
1301.424
5.293
008
60
Error
245.857
Internode 3 Length
1484.934
8.499
007
Error
60
174.709
1484.934
8.499
Internode 3 Area
001
Error
174.709
528
Holdfast Area
787495.018
592
Error
1490496.927
3.868
026
Bushy
11.263
60
Error
2.912
797193.379
1.044
358
Stalk Area
60
763711.483
Error
133375E414
006
Breaking Strength
5.650
60
236054E113
Error
Table 6. Mean ratio of area to length for 10 plants from each site.
Site
Ratio (mim?)
HMS
4199
LVR
3279
PTP
319
Table 7. One way ANÖVA on mean breaking strengths
SUMMARY
Groups
Average
Variance
HMS
103
1.82E112
2468543
2.67E111
LVF
116
1133765
PTF
114
2880860
2.3E112

ANOVA
Source of
MS
F P-value
Variation
Between
9.56Et13 66.19 60.001
Groups
330 1.44E+12
Within Groups
Tot.
332
Figure Legends
Figure 1. Map of study sites along Monterey Peninsula. The inset shows a
closeup of the peninsula with the study sites labeled.
Figure 2. Morphology measurements
a. Measurements made upon each thallus. (a) the number of stipes emerging
from each holdfast. (b) dimensions of the cross sectional area of the stalk. (c)
dimensions of cross sectional area of holdfast. (d) length of thallus.
b. Measurements made upon randomly selected frond in each thallus. The
internode lengths and cross sections were measured. An internode is defined as
the distance from one fork to the next. Internodes are numbered with integers.
The internode numbered "0" is the one which emerges from the holdfast before
any branching begins.
Figure 3. Distribution of Pelvetia at three sites. Significant comparisons (ps
0.05 as determined by a Tukey's test) are marked by a """ while non-significant
comparisons are marked "ns". Error bars illustrate +- one standard error.
a. Percent cover of Pelvetia at three sites.
b. Density of Pelvetia in number of individuals per m2.
Figure 4. Morphological features with significant univariate F-tests. Significant
differences (p20.05 as determined by a Tukey's test) are marked by a * while
non-significant differences are marked by "ns". Error bars illustrate +/- one
standard error.
(a) Lengths of internodes 1-3 at HMS, LVR, PTP in millimeters.
(b) Cross-sectional areas of internodes 1-3 at HMS, LVR, PTP in millimeters?,
(c) Bushiness at HMS, LVR, PTP. The internode number on the y-axis was
determined by the convention illustrated in figure 2.
Figure 5. Scatter plot of the separation of three populations based upon
morphology and breaking strength. The x-axis (factor 1) is a combination of
variables which maximizes differences among sites. The y-axis (factor 2) is a
second combination of morphological variables with the second largest
difference among sites but is also statistically independent from factor 1.
Figure 6. Cumulative probability curve of breakage versus breaking strength.
The applied stress (breaking strength) is shown on the x axis with the probability
of breaking at that stress shown on the y axis. This curve illustrates that for a
given stress, plants at LVR are much more likely to break than those at PTP or
HMS.
Scale in miles
1/4 1/2 3/4
PTE
S
10'
LVR
Figure 1. Map of Monterey Peninsula
HMS
Monterey Peninsula


122° W


50
Figure 2. Morphology measurements
a. Measurements on each thallus
a.


6
—c—

b. Measurements on each frond
2.0

0.5
00
20
15
40
30
20
10
Figure 3a. Percent cover
Lovers
Pt Pinos
□Percent Cover
Hopkins

Figure 3 b. Density (number of individuals per m“2)
Pt Pin
UDensity (Number of
Individuals per m'2)
Lovers
Hopkins
Figure 4a. Internode Lengths
Internode
Figure 4 b. Internode Areas
Intemode
HOPKINS
ELOVERS
OPT PINOS
EHOPKINS
ELOVERS
OPT PINOS
5

Hopkins

Figure 4 c. Bushiness
Lovers



Pt Pinos
DBUSIN
C

90

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ape
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C

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