Abstract
Human activity at Point Pinos, a popular rocky intertidal site in Pacific Grove, CA, was
quantified over a period of seven weeks from April 6, 2000 to May 28, 2000. Over 17.000
people were observed over the 7 weeks. Intensity of activity varied greatly among 9 contiguous
sites within Pt. Pinos, ranging from 12 to 36 people ha sweep (averaged over the 7 weeks for
each site). There was also a high degree of day-to-day variation with daily values ranging from
220 to nearly 700 per sweep, pooled over the entire Point. Of all visitors, only 18% ever entered
the rocky intertidal zone itself, with 280% remaining in the parking lots or on the sandy beach
areas. Data indicated that collecting, or taking of shells or invertebrates, occurred rarely.
Trampling appeared to be the greatest potential impact on sessile species located in the high and
mid intertidal zones. A comparison of the abundance of potentially susceptible (i.e. Pelvetiq
compressa) and non-susceptible (i.e. limpets) sessile species between high-use and low-use Sites
indicated that bare space increases at the high-use Sites. The abundance of non-susceptible
species did not differ significantly between Sites, whereas the abundance of susceptible species
decreased in the high-use Sites. Significant spatial variability between Sites revealed that
differences in species abundance between high-use and low-use Sites cannot solely be attributed
to trampling; hence, other factors such as sand scour and wave action may have contributed to
the heterogeneity.
Introduction
Disturbances are important factors in determining community structure in the rocky
intertidal. The spatial extent, frequency, intensity and season of a disturbance are important
factors determining its effect on the rocky intertidal community (Sousa 1985). As human
populations rise, anthropogenic disturbances in the intertidal will most likely increase in extent,
frequency and intensity. Coastal development may influence intertidal communities with
discharged sewage, industrial effluents and polluted run-off (Murray et al. 1999). Visitors to the
rocky intertidal can also extensively affect intertidal populations by overturning rocks for
scrutiny, collecting organisms for food or bait and trampling on plants and animals (Beauchamp
and Gowing 1982; Povey and Keough 1991; Brosnan and Crumrine 1994; Fletcher and Frid
1996; Murray 1997; Murray and Gibson 1997; Keough and Quinn 1998; Schiel and Taylor 1999;
Brown and Taylor 1999)
Collecting may result in reduced populations of the exploited species (Griffiths and
Branch 1997). Human’s preferential selection for larger organisms can inhibit the population's
reproductive success (Branch 1975; Wells 1997). Trampling can disturb intertidal communities
by crushing or dislodging plants and animals (Beauchamp and Gowing 1982; Povey and Keough
1991; Murray and Gibson 1997; Schiel and Taylor 1999; Brown and Taylor 1999). This
reduction or removal of organisms may also indirectly affect the intertidal community via
changes in competition, predation and habitat provision interactions (Brosnan and Crumrine,
1994).
Despite local concerns, no study has investigated the character or effects of human
activity at Point Pinos in Pacific Grove, California. We investigated the patterns of human
activity at Point Pinos, focusing primarily on the rocky intertidal. We tried to establish which
human disturbances, i.e. collecting or trampling, were important on a local scale before sampling
at different Sites at Point Pinos to assess intertidal community change.
The aim of this study was to estimate the intensity of human use and potential
disturbance, to provide baseline data for future studies to establish a reasonable and quantitative
foundation for management and conservation of the Point Pinos rocky intertidal.
Materials and Methods
Point Pinos is located on the central coast of California, USA (36°38N, 121°57W)
directly north of Asilomar State Beach in Pacific Grove. Point Pinos is part of the Pacific Grove
Marine Gardens Refuge and is regulated by the California Department of Fish and Game. Unlike
most of the California coastline, it has a rocky intertidal which is easily accessible to its visitors.
This feature makes it an attractive place for tourist, locals and school classroom visits.
Wrapping around the northern-most point of the Monterey Peninsula, the study region
spans a length of approximately 1600 meters. Half of the region is exposed to the Pacific waters,
whereas the other half lies in the more protected Monterey Bay. The shoreline along the point
varies from steep rocky bluffs to sandy beaches. The rocky intertidal itself is even more irregular,
varying from a steep rock bench to gently sloping boulder fields. All of these attributes make
Point Pinos highly spatially variable (see Table of Descriptions in Appendix).
The study region was subdivided into nine contiguous Sites to determine patterns of
human activity relative to public access (parking lots)(Fig. 1). Boundaries between Sites were
also drawn according the observable viewing area. Each Site differed in length along the
shoreline and total surface area. The Sites were designated as follows (from east to west around
the Point): Lot 1, Lot 2, Golf Course, Banana, Point Beach, Vertical, Corner, Beach 2, and Great
Tidepool.
Each Site was subdivided into three Zones: Parking Lot, Shore and Intertidal. The
Parking Lot was defined as the area designated for vehicles (i.e. cars, buses, bikes, RV's) and the
foot-trails between lots. The Shore zone encompassed the area that always remains above highest
high tide, which was usually a sandy beach or rocky bluff. The Intertidal zone was divided
further into High (24ft above Mean Lower Low Water), Mid (0-4ft above MLLW), and Low
(SOft above MLLW) Intertidal. Boundaries of the three intertidal zones at each Site were
determined using a laser surveyor's transit relative to benchmarks of the known height.
Documentation of Human Visitation
Human activity was documented everyday, except for Easter Sunday, between April 6
and May 28, 2000. We sampled 2 hours before and after the time of predicted low tide, for this is
when the intertidal is exposed and is most vulnerable to human disturbance. Some samples at
high tide were also taken to detect any differences in visitation according to tide height.
Observations were performed only during daylight hours.
A sample from a Site constituted a snapshot in time, when each person's location and
activity was documented for that day and particular time. Observations were made by first
beginning in Lot 1, sampling, then moving onto Lot 2, sampling, and continuing this procedure
through each Site until the sampler reached Great Tidepool. The completion of the 9 sampled
Sites constituted what we termed a "sweep" of the study region. It took approximately 30
minutes to document one sweep.
Activities that we recorded included fishing, walking, climbing, sitting, sitting in car,
standing, research, tidepooling, collecting, other and unknown. We denoted "collecting" as the
taking of dead animals (i.e. shells) or living invertebrates. If we saw a person with some kind of
container (plastic bag, bucket) or saw a person in the act, then the visitor was described as
collecting. "Tidepooling" described any person who was in the intertidal and was activity
observing the intertidal organisms, but not collecting them. "Unknown" included any person who
had either just arrived or just left the site when the sampler was sampling. "Research" described
people who were tracking sea otters for Sea Ötter Research and Conservation (SORAC) headed
by the Monterey Bay Aquarium. "Other" encompassed activities such as driving through the
parking lot and playing soccer on the beach.
We recorded other factors such as the number of cars, bikes, buses, and pets. The
presence of a ranger, which usually entailed just a drive-by, was also noted. Lastly,
meteorological information such as tide height, temperature, wind speed, swell size, and sky
condition was logged.
Analysis of Human Activity Data
As the surface area of each Site differed, we standardized the counts in each Zone within
a Site to a per hectare (ha, 10' m2) basis. This measure permits direct, meaningful comparisons of
usage among Sites. This new unit, labeled Intensity, was calculated by dividing the count in à
given Site and Zone by the surface area of that zone and by the total number of sweeps. The units
of Intensity are therefore count ha" sweep". Areas were estimated from an aerial photograph of
the study region. The surface areas of high, mid, and low intertidal zones could not be
determined separately, so only total intertidal Intensities could be calculated. Data were analyzed
to detect both spatial and temporal patterns of human visitation along Point Pinos as well as for
the frequencies of each activity.
Assessment of Biotic Community
In order to investigate the potential impact of trampling on the intertidal community at
Point Pinos, we compared two high-use and two low-use Sites based on the average intensity of
intertidal use at each Site. We tested for differences in species abundance and distribution among
the four Sites by running six randomly placed transects at each Site. The transects were all
approximately +2ft (+0.6m) above mean lower low water because the human activity data
indicated that most intertidal activity occurred in the mid intertidal (see Results). There were five
25m’ quadrats distributed randomly along each 1Om transect. We estimated percent cover of all
the sessile species present, bare space and sand in each quadrat. Bare space was rock with
nothing growing on it. We also estimated the total number of limpets in each quadrat by
averaging the limpet count in four of the sixteen sub-divisions and multiplying by 16. We did not
differentiate between limpet species (which included Lottia pelta, Lottia digitalis, Lottia
limatula, Macclintockia scabra and Tectura scutum) because it was often too difficult to identify
them properly. We included limpets because they are small organisms with a hard shell that are
less susceptible to trampling than fleshy algae. We considered both susceptible and non-
susceptible species in order to detect natural variation between the Sites, independent from
human foot traffic.
The upper mid-intertidal community at Point Pinos is composed primarily of the red
algae Mastocarpus papillatus, Mazzealla affinis and Endocladia muricata. They often grow
close together, forming dense low-lying mats that are probably moderately susceptible to
trampling. The general morphology of M. papillatus and M. affinis are similar, both growing one
or more thalli from a disc-shaped holdfast. The equally divided blades are relatively broad,
growing to 10-15cm and 5-1Ocm, respectively. M. papillatus often has small bumps on the
blades and is red-brown to black. Thalli of M. affinis tend to be smoother and lighter in color,
from dark brown to olive green. The compact bushy E. muricata grows 4-6cm tall and is dark red
to blackish-brown (Abbott and Hollenberg 1976). The brown alga Pelvetia compressa is also
present and is probably more susceptible to trampling due to its morphology. The olive green
alga grows from a conical holdfast, extending 15-40cm. The fleshy thalli are usually cylindrical
near the base and compressed near the tips (Abbot and Hollenberg 1976). Various corallines and
other encrusting algae are also abundant. Corallina spp. are mostly purple or pink. The upright
form has many erect, branched, jointed thalli while the encrusting form produces a calcified crust
on the rock. For the purpose of this study, we grouped all the corallines when estimating percent
cover. The other encrusting algae that we encountered most frequently was the tetrasporic
"Petrocelis" stage of Mastocarpus that grows as a tar-like crust on the rocks.
Statistical Analysis
The percent cover or number of species was tested by a two-factor nested analysis of
variance (ANOVA), with the factors being Sites (fixed) and Transects-within-Sites (random).
The quadrats along each transect provided the replicates. The homogeneity of variances was
tested using Cochran’s test (Winer, 1991) and an arcsine transformation was performed on the
ratios before analysis. All tests were conducted at the 0.05 level. Following the initial ANOVA,
planned comparisons were carried out between the averages of the high-use and low-use Sites.
Results
Human Activity
Observations over fifty days produced the following temporal and spatial patterns of
visitation, frequency of activities, mode of transportation, and presence of range
Temporal Patterns
Time of Day Visits to Point Pinos were not distributed uniformly throughout daylight hours.
Highest counts in the Parking Lots and along the Shore (pooled over all days and Sites) occurred
after midday (1 lam - 9pm, Fig. 2B). Counts during morning hours (6-1 lam) were consistently
low. Activity in the intertidal zone itself peaked at midday (Fig. 2A).
Tide Height Visitation varied according to the state of the tide (Fig. 3). A majority of the
visitors came when the tide was below +4ft above MLLW.
Day of the Week Average intensity of use at Point Pinos increased toward the end of the week
and was greatest during the weekends (Fig. 4). The average intensity for weekends was more
than twice that of weekdays. Some weekdays had a distinctly higher average intensity than the
other weekdays due to tour buses or large school groups. The highest recorded intensity of use
occurred during Memorial Day Weekend, the last weekend sampled.
Monthly Patterns Total intensity of use increased toward the end of the spring months (Fig. 5),
with a high degree of day-to-day variation. No clear monthly pattern for intertidal intensity was
evident, except for a noticeably higher level during Memorial Day weekend.
Spatial Patterns
Between Sites Intensity of use varied greatly among the 9 contiguous Sites along Point Pinos
(Table in Appendix). Banana, Point Beach, Vertical, and Corner received the greatest total
intensity of use (i.e. summed over all Zones), whereas Great Tidepool and Lot 1 experienced the
least.
Between Sites and Zones Visitors to the Intertidal zone comprised a small fraction (18%) of the
total visitors to Point Pinos; the remaining 82% were on the Shore (above the intertidal zone) or
in the Parking Lot (Table in Appendix, Fig. 6). In all but two Sites, the intensity of use across the
different zones (ranked from highest to lowest) were Parking Lot, Shore, and Intertidal. Banana,
Point Beach, Vertical, and Corner ranked the highest in parking lot usage. Lot 2, Point Beach,
and Beach 2 were the top three Sites for shore usage. Lot 2 and Point Beach had the greatest
intertidal intensity of use, whereas Lot 1 and Vertical had the least (Fig. 7).
Between Sites and Intertidal Zones Of the visitors who entered the intertidal zone, most
remained in the high (° 4ft above 0 MLLW) and mid intertidal (0-4ft above O MLLW) (Fig. 8).
76% of all intertidal activity occurred in the mid intertidal. Lot 1, Lot 2, Banana, and Point Beach
lacked a high rocky intertidal zone, due to sand cover. Corner, Beach 2, and Great Tidepool
experienced the greatest intensity of use in the low intertidal; however, only 3.5% of all intertidal
visitors entered the low intertidal (Table in Appendix).
Frequencies of Activities Of the total number of visitors to Point Pinos, approximately 35%
were sitting in their cars; 20% were walking; 14% were sitting; 10% were standing; and 9% were
tidepooling. Approximately 1% of the total visitors were fishing. All other labeled activities each
comprised 5% of the total number of observed activities (Table in Appendix). Within the
Intertidal zone, the most frequent activities were tidepooling, walking, and climbing. Of the
3,149 intertidal visitors, 120 were collecting (#4%), defined as the taking of shells or
invertebrates. Most of the collectors appeared to be taking shells, rather than living invertebrates.
No tools were ever seen.
Preferred Sites for Particular Activities More people tended to tidepool at Lot 2, Golf Course,
and Point Beach than at any other Site (Table in Appendix). Visitors were least inclined to
tidepool at Lot 1 and Vertical. Fishermen preferred Lot 1 and Point Beach the most and Corner
and Beach 2 the least. A majority of the collecting (taking of shells or invertebrates) took place at
Lot 2, Beach 2, and Great Tidepool. Collecting was rare at Banana and Vertical. "Sitting in the
car" was a more common activity at Banana, Point Beach, Vertical, and Corner. It was less
frequent at Lot 1 and Great Tidepool. "Öther" activities (mainly driving through the parking lot)
was the most frequent at Banana, followed by Point Beach, and then Vertical.
Frequency of Various Modes of Transportation Total counts of cars, buses, and bikes produced
a ratio of 157:5:1, which indicated that a majority of the visitors drove to Point Pinos (Table 1).
Ranger Sitings Of the 233 total samples we took, we saw rangers approximately 2% of the time
(usually just driving by on the main road) (Table in Appendix).
Meteorological Data No tabulations were performed to determine intensity of use relative to
temperature, swell size, wind speed, and sky conditions. The recorded temperature, swell size,
and wind speed were taken from measurements taken 30 miles away and, therefore, did not serve
as accurate descriptors for the conditions at Point Pinos. We decided that tabulating counts of
people by weather conditions would not reveal any novel pattern of activity which was not
already known (i.e. more people were there on warm sunny days than cold overcast windy ones).
Sampling Results
After quantifying the frequencies of the various activities, we found that collecting and
fishing comprised an extremely low percentage (22%) of the total number of activities recorded.
We felt that these activities occur too rarely to have a measurable impact on the sessile flora and
fauna. People walking across the rocks on the high and mid-intertidal zones far outnumbered
those collecting or fishing. Hence, we decided that trampling posed the greatest potential threat
to rocky intertidal communities.
Potential trampling was most concentrated at Lot 2 and Point Beach, whereas Lot 1 and
Vertical received very little foot traffic. However, Lot 1 and Vertical could not be used as Sites
for low-use comparison because their physical characteristics were extremely different from
those of Lot 2 and Point Beach. The intertidal substratum of Vertical comprised steep rock
bench, whereas both Lot 2 and Point Beach had gently sloping boulder fields. The intertidal area
at Lot 1 was too small to run all six transects at the desired tide height. The most comparable
low-use Sites were Banana and Great Tidepool, both of which had a rocky intertidal composed of
boulder fields at the desired tide height.
Mats composed of M. papillatus, M. affinis and E. muricata were present at all four sites,
as were corallines and encrusting algae (Table 1). The low-use sites, Banana and Great Tidepool,
had much more diverse communities, including P. compressa, Mazzealla flaccida, Fucus
gardneri and Anthopluera spp.. These species were present at Point Beach as well, but in far
smaller numbers (35% within a quadrat), and were completely absent at Lot 2. The algae, such as
Cladophora sericea and Gastroclonium subarticulatum, that were rare (§1% within a quadrat) in
the low-use Sites were not observed in the high-use Sites.
Throughout our sampling many species were observed but only eight were abundant
enough to analyze statistically (Table 2). There were significant differences between high-use
and low-use Sites for both bare space and P. compressa. Bare space was considerably lower at
Banana and only slightly lower at Great Tidepool compared to the two high-use Sites (Fig. 9).
There was significant variation between transects within each site, except at Banana. P.
compressa was virtually absent at the high-use Sites, while cover was between 8% and 10% at
the low-use Sites (Fig. 10). There was also significant variation between transects at the Sites
where P. compressa was present, indicating patchy species distributions within each Site.
Coralline and E. muricata populations showed significant differences between high-use and
low-use Sites as well. Cover of E. muricata was relatively consistent at Banana, Great Tidepool
and Lot 2, but was considerably lower at Point Beach (Fig. 11). Coralline algae was least
abundant at Lot 2, increasing slightly at Point Beach, and increasing more at the two high-use
Sites (Fig. 12).
There was no significant difference between the high-use and low-use Sites for our non-
susceptible species, the limpets (Fig. 13). All four sites averaged between 0 and 2 individuals per
0.25 m2. However, there was significant variation between transects within Sites, indicating a
patchy distribution on a scale of 10's of meters. There was also no significant difference between
M. papillatus (Fig. 14), M. affinis (Fig. 15) and encrusting algae (Fig. 16) populations at the
high and low use sites. Correspondingly, the species distribution of M. papillatus and encrusting
algae between sites was relatively regular. This is not the case for M. affinis because there was
considerable variation among the low use sites, ranging from 1% to 10% cover. Cover of M.
affinis was very high at Banana, but near zero at Great Tidepool.
Discussion
Patterns of Human Activity
Patterns of human activity were found to vary in both time and space. Generally, visits to
Point Pinos increased as the week progressed, and were most frequent on the weekends.
Beginning in early May, the total intensity of use at Point Pinos began to increase and peaked on
Memorial Day weekend. On one occasion, the combined presence of several school classes and
tour groups played a part in increasing the average intensity of a given weekday summed over all
weeks (e.g. Tuesday). Peaks in the exploitation of sandy beaches by humans have also been
found during the afternoon on weekends, in South Africa (van Herwerden et al. 1989).
Most visitors to Point Pinos never traveled beyond the Parking Lot or Shore. In fact,
"sitting in the car" was the highest ranking activity recorded. Of the visitors who left their cars or
bus, very few entered the rocky intertidal and, therefore, did not have much impact on it. This is
not the case at other marine refuges along the California coast, such as Dana Point Marine Life
Refuge located in southern California, where 1,443 persons visited the rocky intertidal in a single
afternoon (Murray 1997). We sampled for almost two months before reaching just twice that
amount. As fishing and collecting in the Intertidal zone were rare and walking/standing occurred
most often, trampling was the only form of human disturbance that was considered to have a
potentially important direct effect on populations in the rocky intertidal.
Few comparative data have been published on quantitative analysis of human activity in
the rocky intertidal. Most studies have focused on the collection of intertidal invertebrates and,
consequently, employ entirely different sampling methods for human activities. Concerned only
with determining the intense recreational fishing activity at a site located along the coast of New
South Wales, Kingsford et al. (1991) did not consider "walkers" as potential tramplers in the
intertidal community. Although Murray (1997) has performed studies on visitor pressures to the
intertidal in southern California and the possible impact on the abundance of susceptible algae,
his published literature primarily focuses on collecting. To more accurately describe intensity of
collecting by visitors, Murray standardized the counts of people by time, whereas we
standardized the counts by the area of the affected Zone. The lack of uniform sampling methods
for human activity and lack of consistent standardized measurements make comparisons between
our estimated intensities and theirs difficult. A reasonable unit of measure that would permit
meaningful comparisons between different locations would be number of people per time (hour,
day, etc.) per area (ha, acre).
Some Sites, such as Lot 2 and Point Beach, had greater numbers of intertidal visitors than
did others, such as Lot 1 and Vertical. This can partly be attributed to the general features of the
Site such as availability of parking, access to the Shore, and scenic view (see Table of
descriptions in Appendix). This pattern of use is similar to spatial distributions of people found
in Australia, where fishermen were reported as having "favorite fishing spots" (Kingsford et al.
1991).
The high total intensities of use found in the Mid Intertidal Zone were a result of two
factors. First, four of the Sites lacked a High (rocky) Intertidal Zone (e.g. Lot 1, Lot 2, Banana,
and Point Beach). Second, each of the two Sites of the greatest intertidal intensity (e.g. Lot 2 and
Point Beach) had a promontory extending out from the Shore. To get to these points, visitors had
to walk across an isthmus which is approximately +2ft above MLLW at both Sites.
Greater numbers of people tended to visit Point Pinos during mid and low tide. School
classes often take advantage of the minus tides to have better access into the rocky intertidal. As
seen by the error bars in Fig. 3, there is a high degree of variation within each tide height group.
We think that intensity of human activity is more influenced by time of day than by state of the
tide. Future studies should incorporate interviews into their sampling methods in order to gain a
more accurate understanding of visitor activity.
Analysis of Biotic Community
The effects of a disturbance on natural communities depends on its spatial extent,
frequency, intensity and the season in which it occurs. Natural disturbances are usually seasonal
and localized, but trampling tends to be more constant and regular (Keough and Quinn 1998).
Schiel and Taylor (1999) suggest that chronic trampling can prevent recovery by hindering
successful recruitment and re-growth. Therefore recovery depends not only on a reduction or
cessation of human disturbance but also on an adequate source of propagules from healthy,
reproductive adult algae.
Trampling, even in moderate degrees, can effect community structure on rocky shores
and may shift the community to an alternate state. Fletcher and Frid (1996) defined 'recreational
carrying capacity' as only 20 footsteps per m’, applied once every set of spring tides. This is as
few as only five people walking the same path' through the rocky intertidal. Trampling within
portions of the high and mid intertidal at Point Pinos certainly exceeds this intensity of use.
Communities can recover from the effects of trampling although its frequency and intensity
make it a particularly relentless stress (Brosnan and Crumrine 1994; Brown and Taylor 1999).
Intertidal community structure varies considerably from Site to Site along Point Pinos.
This is evident from the statistical analysis of our results, indicating significant differences
among transects within Sites as well as among all four Sites. Despite uneven population
distribution, there is a clear difference between the high-use and low-use Sites. Species are more
diverse and more abundant at the low-use Sites.
There are several ways in which trampling may cause these effects. Trampling is a
disturbance because it can damage or remove species and create patches of bare space (sensu
Sousa, 1985; Brosnan and Crumrine 1994; Kim and DeWreede 1996). Povey and Keough (1991)
found persistent trampling results in the replacement of algal communities with bare rock.
Bare space is highest at our two high-use Sites, Lot 2 and Point Beach. Although bare
space is also relatively high at Great Tidepool, P. compressa and other susceptible algae make up
a considerable portion of the cover there, suggesting that trampling is less severe at this Site.
Studies show that foliose species, such as P. compressa and Fucus gardneri, are particularly
susceptible to trampling because their small holdfasts connect them to the rock only at a single
point (Povey and Keough 1991; Beauchamp and Gowing 1982). Trampling also crushes and
breaks their elongate, fleshy thalli, destroying valuable reproductive organs (Murray 1997). In
our study, these susceptible species are entirely absent from Lot 2 and nearly absent from Point
Beach.
These large algae provide habitat heterogeneity by generating a protective canopy,
shielding underlying species from heat stress and desiccation. The removal of these protective
canopy species can significantly alter the community composition, opening bare space for
colonization and selecting for less susceptible algal species (Beauchamp and Gowing 1982).
Brown and Taylor (1999) found reduced animal densities resulting from the loss of algae cover
and associated sand. We did not quantify the mobile animals in our study, but qualitative
assessments suggest that chitons, crabs and various molluscs are more abundant at the high-use
Sites, beneath the canopy (personal observation). Keough and Quinn (1998) observed coralline
bleaching and fragmentation due to sun exposure associated with the reduction of the over-lying,
protective canopy. In our study, there is a significant difference between coralline algae
populations between the high-use and low-use Sites.
Canopy can provide protection against desiccation, but it can also prevent settlement
through whiplash, shading or space occupancy (Kim and DeWreede 1996). Correspondingly,
Brosnan and Crumrine (1994) observed that foliose species replaced turf forms when trampling
was prevented in experimental plots.
Turf and encrusting algae tend to be less susceptible to trampling because of their
morphology. Turf species' thalli are usually short and repeatedly branched. They also spread
vegetatively and are attached to the rock at many points, making them more resistant to
trampling (Beauchamp and Gowing 1982). In trampled areas in North America there has been a
shift in the algal community from larger species to turf-like forms (Beauchamp and Gowing
1982; Brosnan and Crumrine 1994). Our data also show this trend with the turf species (E.
muricata, M. affinis and M. papillatus) present at all four Sites, but the larger, more susceptible
species (P. compressa and F. gardneri) nearly absent in the high-use Sites. M. affinis and M.
papillatus populations are not significantly different between the high-use and low-use Sites,
suggesting that trampling is not intense enough to alter their species composition at the high-use
Sites.
Reduced species diversity can be a result of stress in the rocky intertidal (Beauchamp and
Gowing 1982). In our study, the low-use Sites have considerably higher algal diversity than the
high-use Sites. Lot 2 is particularly homogeneous, primarily filled with bare space, E. muricata,
M. affinis and M. papillatus.
Our data are consistent with what we would predict from the effects of trampling, but
they are not conclusive. Although our non-susceptible species, the limpets, show no significant
difference between the high-use and low-use Sites, suggesting that there is little natural variation
among the Sites, this is probably not the case. Many of the differences between the high and low
use sites cannot be attributed solely to human disturbance because of many potentially
confounding factors.
The large rock promontories located at the high traffic sites, Lot 2 and Point Beach, are
very popular for climbing and sitting. But they are more significant than merely drawing visitors
into the intertidal in order to access them. These promontories affect wave action around the
point, shielding some areas of the intertidal from wave energy and concentrating it in other areas.
At low tide, the rocky intertidal is exposed between the promontories and the main portions of
the shore. But the water starts to cover the isthmuses when it rises above +2ft MLLW, generating
a strong current. This is important because the current's unidirectional flow creates friction and
carries suspended material that can erode the algae from the rocks.
Water movement can also produce natural disturbances, such as moving small rocks and
overturning boulders when wave energy is high enough. Öther natural disturbances, such as
burn-off from sun exposure or the presence of marine mammals, can also generate significant
differences between sites. Otters and seals are frequently present at Great Tidepool and only
occasionally at the other Sites. They affect the rocky intertidal by eating organisms and by
hauling out on the rocks.
All four sites are located near sandy beaches. The sand covers the high rocky intertidal at
Lot 2, Point Beach and Banana. Point Beach and Lot 2 also experience relatively high wave
energy, possibly suspending large particles in the water that can scrape algae from the rocks.
Öther heterogeneities between the Sites include varying slopes of the intertidal,
differences in boulder sizes and type of subtratum beneath the boulders. The slope of the
intertidal is important because different species colonize at different heights in the intertidal. The
intertidal at Lot 2 extends horizontally for 20 meters at approximately the same height before
descending sharply into the subtidal. In contrast, Banana slopes gradually but consistently from
the shore to Oft MLLW. Although all four Sites are primarily boulder fields, the rock sizes vary
with the largest generally at Great Tidepool and Point Beach and the smallest at Lot 2. The
substrate beneath the boulder fields also varied from sandy to large rock benches between Sites,
as well as within Sites.
These factors all differ considerably among the Sites and contribute to the differences
found in species' distribution and abundance between the high-use and low-use Sites. Therefore
we cannot attribute the differences found between the high-use and low-use Sites to trampling
alone.
Even if trampling is not the only cause of the differences between the high-use and low-
use Sites, it may be having a considerable effect. Our study only provides a snap-shot survey of
Point Pinos in the spring. The study's limited spatial and temporal scales make it difficult to fully
understand the intertidal community composition. Consequently, there needs to be prolonged
studies in order to gain a better understanding of the effects of human activity on the rocky
intertidal at Point Pinos. Trampling manipulations on local algae species, such as M. affinis, M.
papillatus and E. muricata, would provide valuable information, demonstrating their
susceptibility to human foot traffic and the sustainable level of foot traffic that each species can
tolerate. We also recommend fencing off areas within each site to observe if percent cover
increases without any trampling. These fenced off areas would also serve as a control, helping
identify natural disturbances.
The next step is a long-term analysis of human activity at Point Pinos coupled with
periodic sampling in order to detect seasonal variation in human activity as well as in intertidal
community composition. This will establish the timing of the disturbance, an important factor
when considering species recruitment and colonization. The sampling should include both
susceptible and non-susceptible species so that differences between populations can be attributed
to trampling and not some other disturbance. Ideally, a long-term study should employ control
sites with the same substrate and physical characteristics, but no human activity. These pristine
sites would provide an excellent point of comparison for susceptible and non-susceptible species,
controlling for natural disturbances and seasonal variation. Only if susceptible species decline at
the Point while remaining constant or fluctuating at the control site and if non-susceptible species
do not decline at either site, would there be unequivocal evidence for human impacts.
Acknowledgments
We thank our advisor, Jim Watanabe, for his help and invaluable advise through every
step of this project. We have enjoyed his enthusiasm for our project, his confidence in us and his
selfless devotion of his time and energy to teaching. We would also like to thank Luke Hunt for
his assistance in the field and Chris Patton for his technical expertise. Lastly, we thank the
visitors at Point Pinos for their patience.
References
Abbott, I. A. and G. J. Hollenberg. 1976. Marine algae of California. Stanford Univ. Press, Stanford, CA. pp. 827.
Beauchamp, K. A. and Gowing, M. M. 1982. A quantitative assessment of human trampling effects on a
rocky intertidal community. Marine Environmental Research, 7: 279-293.
Branch, G. M. 1975. Notes on the ecology of patella concolor and Celana capensis, and the effects of
human consumption on limpet populations. Xoology Africana. 10: 75-85.
Brosnan, D. M. and Crumrine, L. L. 1994. Effects of human trampling on marine rocky shore
communities. Journal of Experimental Marine Biology and Ecology, 177: 79-97.
Brown, P. J. and Taylor, R. B. 1999. Effects of trampling by humans on animals inhabiting coralline algal
turf in the rocky intertidal. Journal of Experimental Marine Biology and Ecology, 235: 45-53.
Fletcher, H. and Frid C. L. J. 1996. Impact and management of visitor pressure on rocky intertidal algal
communities. Aquatic Conservation: Marine Freshwater Ecosystems, 6: 287-297.
Griffiths, C. L., and G. M. Branch. 197. The exploitation of coastal invertebrates and seaweds in South Africa:
historical trends, ecological impacts and implications for management. Transactions of the Royal Society of
South Africa, 52: 121-148
Keough, M. J. and Quinn, G. P. 1998. Effects of periodic disturbance from trampling on rocky intertidal
algal beds. EcologicalApplications, 8(1): 141-161.
Kim, J. H. and DeWreede, R. E. 1996. Effects of size and season of disturbance on algal patch recovery in
a rocky intertidal community. Marine Ecology Progress Series, 133: 217-228.
Kingsford, M.J., Underwood, A. J., Kennelly, S. J. 1991. Humans as predators on rocky reefs in New South Wales
Australia. Marine Ecology Progress Series, 72: 1-14.
Murray, S. N. 1997. Effectiveness of Marine Life Refuges on Southern California shores. Precedings of the
Conference of American Society of Civil Engineers, San Diego, California. pp. 1453-1465.
Murray, S. N. and Gibson, T. A. 1997. Vulnerability of the rockweed Pelvetia compressa to anthropogenic
disturbance on southern California rocky shores. Phycologia, 36: 75-76.
Murray, S. N., Denis, T. G., Kido, J. S., and Smith, J. R. 1999. Human Visitation and the Frequency and
Potential Effects of Collecting on Rocky Intertidal Populations in Southern California Marine Reserves.
CalCOFI Rep, 40: 100-105.
Povey, A. and Keough, M. J. 1991. Effects of trampling on plant and animal populations on rocky shores.
Oikos, 61: 355-368.
Schiel, D. R. and Taylor, D. l. 1999. Effects of trampling on a rocky intertidal assemblage in southern New
Zealand. Journal of Experimental Marine Biology and Ecology, 235: 213-235.
Sousa, W. P. 1985. Disturbance and patch dynamics on rocky intertidal shores. pp 101-124 in S. T. A.
Picket and P. S. White, eds. The Ecology of Natural Disturbance and Patch Dynamics, Academic Press,
London.
van Herwerden, L., Griffiths, C. L., Blaine, M., and du Plessis. 1989. Patterns of shore utilization in a
metropolitan area at The Cape Peninsula, South Africa. Ocean Shore Management, 12: 331-346.
Winer, B. J. 1991 Statistical principles in experimental design. McGraw Hill, New York, NY. pp. 907.
Wells, S. M. 1997. Giant clams: status, trades, and mariculture, and the role of CITES in management. World
Conservation Union, Gland, Switzerland. IUCN Communications division, pp. 77.
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Table 1. A list of all the limpet species we encountered over the Sites. We grouped all limpets together
while counting due to the difficulty of identifying the different species properly. Also, lists of all sessile
species recorded at each Site. We grouped all Corallina spp. when estimating percent cover as well.
Encrusting algae’ refers to the tetrasporic "Petrocelis" stage of Mastocarpus spp.,
Limpets (present at all sites):
Lottia pelta
Lottia digitalis
Lottia limatula
Tectura scutum
Macclintockia scabra
High Use Sites:
Point Beach
Lot 2 Mazzaella affinis
Mazzaella affinis
Mastocarpus papillatus
Mastocarpus papillatus
Endocladia muricata
Endocladia muricata
Encrusting algae
Encrusting algae
Coralline algae
Coralline algae
Pelvetia compressa
Fucus gardneri
Mazzaella flaccida
Anthopleura elegantissima
Low Use Sites
Great Tidepool Mazzaella affinis
Banana
Mazzaella affinis
Mastocarpus papillatus
Mastocarpus papillatus
Endocladia muricata
Endocladia muricata
Encrusting algae
Encrusting algae
Coralline algae
Coralline algae
Pelvetia compressa
Pelvetia compressa
Fucus gardneri
Fucus gardner
Mazzaella flaccida
Mazzaella flaccida
Pelvetia compressa
Pelvetia compressa
Gastroclonium subarticulatum
Gastroclonium subarticulatum
Cladophora sericea
Cladophora sericea
Anthopleura elegantissima
Anthopleura elegantissima
Anthopleura sola
Anthopleura sola
Prionitis lanceolata
Mytilus californianus
Phyllospadix scouleri
Haliclona spp.
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Figure Legend
Fig. 1. The nine study Sites at Point Pinos, with dotted lines indicating parking lots. Lot 2 and Point Beach
were the high-use Sites. Great Tidepool and Banana were the low-use Sites. See the appendix for the area
(in hectares) of each of the three zones within each Site. See the appendix for descriptions of each Site.
Fig. 2. Average people sweep" in the intertidal (A), and in either the parking lot or shore (B), summed over
the entire Point in the morning, midday and evening. Number of sweeps taken at each time of day written
above columns. Error bars represent the standard error of the mean.
Fig. 3. Average people sweep" summed over the entire Point at low, mid and high tide. Tide height in feet
above mean lower low water. Number of sweeps taken at each tide height written above columns. Error
bars represent the standard error of the mean.
Fig. 4. Average intensity per day of the week in people ha" sweep" summed over the entire Point. Circles
represent the average intensity for a given day within a given week. The line connects the average intensity
for a given day summed over all the weeks.
Fig. 5. Average daily intensity in people ha" sweep" summed over the entire Point for the months of April
and May. The dashed line represents the total average intensity in all three zones. The solid line shows the
average intensity in only the intertidal.
Fig. 6. Average intensity in people ha" sweep" for each of the three zones within each Site.
Fig. 7. Average intensity in people ha" sweep" in the intertidal at each Site.
Fig. 8. Percent of intertidal visitors in the high, mid and low intertidal at each site. The total count of
visitors to the intertidal for each Site is listed above the columns.
Fig. 9, Percent cover of bare space per 0.25 m2 at each Site sampled. There were 6 transects, each with 5
quadrats, at each Site. Low-use Sites are on the left and high-use Sites are on the right. Circles represent the
mean percent cover per 0.25 m2 for each transect within each Site. The line connects the mean percent
cover per 0.25 m2 at each Site.
Fig. 10, Percent cover of P. compressa per 0.25 m2 at low-use and high-use Sites. There were 6 transects,
each with 5 quadrats, at each Site. Figure format as described in fig. 9.
Fig. 11. Percent cover of E. muricata per 0.25 m2 at low-use and high-use Sites. There were 6 transects,
each with 5 quadrats, at each Site. Figure format as described in fig. 9.
Fig, 12, Percent cover of coralline algae per 0.25 m2 at low-use and high-use Sites. There were 6 transects,
each with 5 quadrats, at each Site. Figure format as described in fig. 9.
Fig. 13. Mean number of limpets per 0.25 m2 at each Site sampled. There were 6 transects, each with 5
quadrats, at each Site. Low-use Sites are on the left and high-use Sites are on the right. Circles represent the
mean number of limpets per 0.25 m2 for each transect within each Site. The line connects the mean number
of limpets per 0.25 m2 at each Site.
Fig, 14. Percent cover of M. papillatus per 0.25 m2 at low-use and high-use Sites. There were 6 transects,
each with 5 quadrats, at each Site. Figure format as described in fig. 9.
Fig, 15. Percent cover of M. affinis per 0.25 m2 at low-use and high-use Sites. There were 6 transects, each
with 5 quadrats, at each Site. Figure format as described in fig. 9.
Fig. 16. Percent cover of encrusting algae per 0.25 m2 at low-use and high-use Sites. There were 6
transects, each with 5 quadrats, at each Site. Figure format as described in fig. 9.
Fig. 1
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Morning (6am-11am)
Fig. 24
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....
Midday (11am-Apm)
TIME OF DAY
Fig. 2B
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Midday (11am-Apm)
TIME OF DAY
33
53 sweeps
.
Evening (Apm-9pm)
53 sweeps
Evening (4pm-9pm)
100
90
80
50
30
20
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low (S 0)
Fig. 3
189 sweeps
mid (0-4)
TIDE HEIGHT (ft)
25 sweeps
high (24)
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