• Ecological Impacts of Human Visitation to Rocky Shores
• Coastal Biodiversity Surveys
|Ecological Impacts of Human
Visitation to Rocky Shores
Rocky shores offer a window into the diversity of marine
life that is accessible to all. As the tide recedes, rocks covered
with algae and invertebrates and tidepools hosting natural aquaria can be explored easily by simply walking along the shore.
Easy access provides a tremendous opportunity for visitors to experience nature and learn about the diversity of solutions
to life in this unique and challenging environment, but it may also pose threats to the marine life that the visitors come to observe. We have been investigating the possible ecological impacts of human visitation of rocky shores by comparing locations with varying amounts of public access and restrictions on use and by conducting experiments that simulate human disturbance on a small scale.
We compared abundance and diversity of algae and invertebrates across eight locations that span a gradient in possi-ble human disturbance, taking advantage of existing marine reserves and other areas that represent different levels of access and legal or de facto restriction of human activities. Field sites included two no-take marine reserves (the Hopkins Marine Life Refuge and the Point Lobos Ecological Reserve); two 'de facto reserves,' where access to the shore is prevented by the presence of fenced estates (Pescadero Point in Pebble Beach and Mal Paso, south of Point Lobos); two sites, within the Point Pinos Marine Gardens Fish Refuge and the Carmel Bay Ecological Reserve, where marine invertebrate collection is prohibited by law but where public access is unrestricted; and two sites that are not within any marine
protected area and are easily accessed from the shore (the rocky shores east of the Monterey Bay Aquarium, accessible from Cannery Row in Monterey, and Soberanes Point, south of Point Lobos). Thus, the eight field sites fall into four categories, each represented by two distinct locations: (1) closed access, no-take reserve, restrictions enforced by on-site personnel; (2) closed access because of coastline morphology and private property along the shore (de facto reserves); (3) open access, restrictions of take because of ecological reserve status but no enforcement by on-site personnel; and (4) open access, no restrictions to collecting other than state-wide regulations.
|Easy access to the sanctuary's rocky shores provides a tremendous opportunity for
visitors to experience nature, but it may also pose threats to the very marine life that these visitors come to observe. (Photo by Steve Lonhart/MBNMS)
In the winter and summer of 2002 and 2003, we estimated
percent cover of algae and sessile invertebrates (those attached to the rocks, including mussels, barnacles and anemones) within
quarter-square-meter plots along transects stretched at different heights along the shore. Small mobile invertebrates, such as limpets and snails, were counted within the same plots. In total, 220 invertebrate and algal taxa were surveyed within 2,304 plots over the course of the two years. Large invertebrates -- the black abalone, Haliotis cracherodii, and the purple sea urchin, Strongylocentrotus purpuratus -- were counted within 30-meter-long, 2-meter-wide band transects. One might expect that rocky intertidal assemblages subject to periodic natural disturbance from wave impacts during storms may suffer little additional damage from people trampling and removing organisms from the rocks. To test the prediction that the effects of human visitation might be apparent at wave-protected locations but may be small compared to natural wave impacts
on exposed shores, we conducted surveys on both wave-exposed
rocky headlands and along stretches of the shore protected by
These comparisons revealed large amounts of natural variability, unrelated to the intensity of human visitation, at these different locations but also significant differences in the abundance and size of particular species and in the overall structure of the rocky-shore assemblages between open-access sites and restricted-access sites (no-take and de facto reserves). Within these broader categories, differences in legal restrictions on take among sites did not explain any additional amount of variation.
Black abalone were larger at restricted-access sites, with indiv-iduals larger than 8 centimeters in length accounting for 14 to 37
percent of all individuals versus 2 to 11 percent of individuals at open-access sites. (See Figure 1, p. 7.) Animals larger than 12
centimeters were found only within restricted-access sites. These size differences, evident despite the fact that a statewide ban on black abalone collecting has been in place since 1993, suggest
that poaching may be occurring at open-access locations. Another conspicuous member of California rocky-shore communities,
the purple sea urchin, had average densities five times greater at restricted-access (1.7 to 4.9 individuals per square meter) than
open-access sites (0.2 to 1.0 individuals per square meter). Finally, preliminary analyses indicate that the overall structure of intertidal assemblages, in terms of the identities and relative abundances of rocky shore species, differed between open-access and restricted-access sites. Contrary to predictions, these differences were apparent only on wave-exposed headlands, not on wave-sheltered shores, and appeared to be associated with a smaller extent of mussel (Mytilus californianus) beds at open-access sites (ranging 3.7 to 15 percent cover across the four locations, 9 percent on average) compared to reserves (8.7 to 29.5 percent cover, 22.6 percent on average). Possible disturbance associated with human uses appeared to add to or interact with natural wave disturbance to cause observable impacts on these communities.
|Figure 1. Size frequency distribution of black abalone at open-access and restricted-access sites
(e.g., no-take and de facto reserves)
The locations we compared differ in a variety of ways beyond just differences in human access and use. There- fore, these population- and community-level differences might not be directly associated with human visitation per se. However, the above results, which suggest possible direct impacts from human visitation on rocky shore communities, were corroborated by experimental results on the effect of one particular type
of human disturbance. We simulated trampling disturbance to
1-square-meter intertidal plots on wave-exposed rocky headlands dominated by mussel beds and at sheltered shores dominated by algal beds located along the Soberanes Point shores. Experimental treatments included trampling levels representative of what we have observed along the Pacific Grove shores (low-trampling intensity); higher disturbance levels documented on rocky shores elsewhere (medium- and high-trampling intensity); and control, undisturbed plots. Treatments were maintained for one year, and recovery was monitored for an additional year, leaving the plots undisturbed during this time. Experimental trampling caused significant reductions in algal cover on wave-protected shores, but only at medium- and high-trampling intensities. (See Figure 2, above.) One year after cessation of disturbance, algal cover in the high-intensity trampling treatments was still lower but statistically indistinguishable from undisturbed controls. In contrast, mussel beds on wave-exposed headlands were significantly reduced, even at the lowest-trampling intensity, and showed no trends towards recovery.
|Figure 2. Changes in mussel and algal cover caused by simulated trampling disturbance of 1-meter-square plots. Low-, medium- and high-trampling intensity corresponded to 20, 100 and 400 steps per month. Percent mussel and algal cover after one year of trampling (black bars) and after a subsequent year of recovery (white bars) are reported.
The rocky shores of the Monterey Bay National Marine Sanctuary provide invaluable opportunities for recreation, education and research. In light of the likely increase of human population densities along these shores, it is crucial to continue to manage and monitor uses of this environment carefully. Species assemblages on exposed shores and long-lived species, including black abalone, sea urchins and mussels, appear to be especially vulnerable to collecting and trampling disturbance and thus are priorities for continued research, education and conservation efforts.
Fiorenza Micheli, Kimberly Heiman, Carrie Kappel, Peggy Lynch,
Jacqueline Martin and Rebecca Martone
Hopkins Marine Station, Stanford University
|Coastal Biodiversity Surveys |
Rocky intertidal reef habitats make up an important part of the coastal ecosystem. Learning more about the community of algae and invertebrates that lives in this habitat is key to understanding and assessing the health of coastal habitats and results in better management and conservation of our coastal oceans.
The Coastal Biodiversity Survey (CBS; http://cbsurveys.ucsc.edu) is a large-scale research project designed to measure diversity and abundance of algae and invertebrates in rocky intertidal communities on the West Coast of temperate North America. This study combines extraordinary precision at the local scale across an expansive spatial scale to create an unprecedented data set for investigating intertidal community structure patterns. With more than 90 sites ranging from Glacier Bay, Alaska to Baja California Sur, Mexico, this study has established a baseline of knowledge that will enable scientists to detect future ecological shifts within and among sites.
The CBS was established to complement both the Partnership for the Interdisciplinary Study of Coastal Oceans (PISCO) monitoring program and the Multi-Agency Rocky Intertidal Monitoring Network (MARINe). A combination of sampling techniques -- including point contact, quadrat and swath bands along transect lines -- is used to determine the abundance of invertebrates and algae, mobile invertebrates and sea stars, respectively. These data are further linked to the elevation of the substrate in relation to
tide levels in order to describe species' vertical distribution.
Results from the CBS have shown that rocky intertidal communities vary with respect to latitude, creating distinct biogeographic regions. Major geographic features such as points and bays along with oceanic currents create boundaries among these regions, which are defined as distinct more by differences in relative abundance of the same species than by differences in species presence.
|Figure 1. Coastal Biodiversity Survey sites in the sanctuary, grouped by
abundance and diversity patterns of algae and invertebrates
The Monterey Bay National Marine Sanctuary lies within the biogeographic region bound by San Francisco Bay to the north
and Point Conception to the south. Within the sanctuary, sites can be further divided into four groups with a similar suite of species but different species abundances. These differences may be driven by a number of variables, such as the slope of the intertidal bench, topographic complexity, type of bedrock, variable ocean currents, water temperatures, sand scouring, human activity and/or runoff. Interestingly, not all groups are contiguous along the coast. (See Figure 1.)
Group 1 contains four sites north of Monterey Bay and one site in Big Sur. Sites within this group all have large, gently sloping benches dominated by algae. Group 2 is made up of two sites at
the northern edge of Monterey Bay. This group is less affected by upwelling due to circulation in the bay, which concentrates warm water in this area. Large mussel beds and barnacles dominate
these sites. Seasonal sand inundations and sand scour may also affect the assemblage of species in Group 2.
Sites found in Group 3 are located south of Monterey Bay. These sites are topographically complex and dominated by algae and mussels. The dominant algae species in Group 3 are similar
to Group 1 but differ in relative abundances. Group 3 sites have
an extensive low zone, creating a perfect habitat for many species that cannot withstand long periods of exposure to the air. Group 4 contains two very steep and exposed sites along the Big Sur coast. Mussels, barnacles and coralline algae are the dominant species cover in this group.
Rocky intertidal communities are both diverse and complex. Species must adapt to endure both the sea's crashing waves
and the sun's desiccating heat. The CBS addresses fundamental questions relating to biogeography, effects of human use, management of coastal resources and conservation at a relevant spatial scale.
Ongoing research will continue to survey these sites every
four years as a long-term monitoring project. Future research may explore the relationship between physical and environmental
variables and the structure of the intertidal community.
Kristen Kusic, Haven Livingston and Peter Raimondi
Department of Ecology and Evolutionary Biology,
University of California Santa Cruz
This project is funded by the David and Lucile Packard Foundation, Gordon and Betty Moore Foundation, Minerals Management Service and Monterey Bay National Marine Sanctuary. Additional support supplied by California State Parks, Fitzgerald Marine Reserve, Gulf of the Farallones National Marine Sanctuary, Hearst Corporation, National Park Service, Pt. Reyes National Seashore and University of California Reserves.