A Study of Visitor Impacts on the Intertidal Zone
at Point Pinos, Pacific Grove
Point Pinos is a prominent rocky headland of the Monterey Peninsula in the Monterey Bay National Marine Sanctuary. Concerns have arisen that the marine life in the Point Pinos intertidal zone is being negatively affected by visitor use, from collecting and displacing organisms, trampling, and simply turning rocks.
|The intertidal zone has become increasingly popular for its educational, recreational, and
scenic values. photo 2003 Scott Kimura
The intertidal zone is the band of shoreline covered and uncovered by the sea between high and low tides. Some of the most diverse marine plant and animal communities occur in wave-swept rocky intertidal zones with outcroppings and tidepools, such as at Point Pinos. These shorelines have become increasingly popular for their educational, recreational, and scenic values and more frequently visited during low tides by schools, tourists, and the local public.
During the summer of 2002 we sampled more than 150 species of invertebrates, algae, and intertidal fishes in multiple band transects and tidepools located in areas of high use at Point Pinos and nearby reference areas of lower visitation. We then statistically analyzed the data for differences in species abundances among areas to determine the levels of visitor impact. A lack of baseline data precluded a comparison to historical conditions. The assemblages studied included a mix of conspicuous species (e.g., turban snails, sea stars, hermit crabs, shore crabs, sea urchins, barnacles, limpets) and less obvious species (e.g., worms, chitons, small snails, abalone in cracks and crevices).
The impact assessment had to consider that biological differences among areas could be present that were not due to visitor use, but rather from natural variation. Therefore, conclusions from our one-time study that visitor use has altered species abundances along the Point Pinos shore required finding consistent, large differences between the visitor use and reference areas in a variety of species that are susceptible to visitor impacts. For example, purple sea urchins were significantly less abundant in tidepools sampled along the Point Pinos shore, relative to tidepools sampled in areas of less visitor use. However, the lack of reduced abundances among other species that are also highly prone to collecting (e.g., turban snails, sea stars, shore crabs, hermit crabs, abalone, limpets) lowers the likelihood that this particular difference was due to visitor impacts. In contrast, there were some apparent differences in algal cover among the areas studied. We found that chronic trampling had likely caused the coverage of some algae to be reduced in portions of the upper intertidal zone near access points.
Excluding visibly trampled areas, we found the Point Pinos intertidal zone to be as diverse as intertidal zones in neighboring shorelines with lower visitation. Overall, biological variation was found to be similarly high both within and among areas of high and low use. This variation also added to the difficulty of detecting greater visitor impacts. Furthermore, marine species in wave-exposed habitats are subjected to a variety of natural disturbances (e.g., wave shear, boulder rolling, sand scour) that are similar to visitor disturbances (e.g., rock turning, trampling). Consequently, it is often difficult to identify visitor impacts in this type of rigorous and heterogeneous environment where high natural biological variation and disturbances can mask the effects of visitor use.
The possibility exists that species at Point Pinos may at one time have been more abundant, but have decreased to the levels found in our reference areas. However, an incomplete knowledge of the historical biological baseline precludes knowing more on how Point Pinos has changed from visitor use versus natural causes. Furthermore, baselines shift, and such changes can only be identified when long-term monitoring data are available for comparisons.
Another possibility as to why greater impacts were not discerned may have been related to several resource conservation measures that were implemented one to three years prior to our sampling
and which may have allowed some impacted species to recover.
In 2002 the Pacific Grove Police Department increased resource enforcement and surveillance of illegal collecting at Point Pinos, and signage in three languages informing visitors not to disturb
the marine life was placed along the shore. BAY NET, an Ocean Conservancy and sanctuary docent program, expanded its conservation awareness instruction to Point Pinos about a year before
our study, complementing similar efforts by the Coalition to Preserve and Restore Point Pinos Tidepools, a public advocacy group. While fishing is still allowed in the area, and certain intertidal invertebrates may still be collected with a fishing license, all other intertidal collecting is prohibited, except with a scientific collecting permit authorized by the California Department of Fish and Game (CDFG). However, in 1999 the CDFG issued a moratorium on scientific collecting in the area.
This one to three year period may have been sufficient for some of the most rapidly reproducing and fast growing species, such as some algal species and smaller invertebrates, to recover. However, this period would not have been sufficient for full recovery in
slower growing species with limited reproduction and propagule dispersal. These include owl limpets, abalone, and sea stars. The lack of substantial findings of adverse visitor impacts in the slower growing species may, in effect, indicate that impacts were not large to begin with, as the abundances of these species were not significantly different between Point Pinos and reference areas.
We estimate that approximately 50,000 people venture down into the Point Pinos intertidal zone annually. Many other shorelines experience greater levels of visitation into the intertidal zone, and resource managers in these areas are faced with similar issues of balancing resource conservation with continued access and uses. Accordingly, we feel that maintaining resource conservation programs at Point Pinos, including monitoring, is warranted in light of the findings of this study, because visitor use will likely increase
in the future with natural population growth.
We thank the David and Lucile Packard Foundation, the City
of Pacific Grove, and the sanctuary for funding the study and the Monterey Bay Sanctuary Foundation for project administration. The Point Pinos Tidepool Task Force Research Committee, a panel of local scientists and citizens, commissioned the study. We would not have completed our study without assistance from BAY NET, which conducted our visitor census surveys. The final report is available at www.mbnmsf.org or on CD from the City of Pacific Grove.
|Withering Syndrome in Black Abalone
Founded in 1999 by the David and Lucile Packard Foundation, the Partnership for Interdisciplinary Studies of Coastal Oceans (PISCO) is a consortium of four west coast universities that focuses on regional-scale, multidisciplinary research related
to coastal rocky reefs. One research project funded under PISCO is the long-term monitoring of black abalone along
the coast of California by researchers at UC Santa Cruz.*
This program surveys fifteen sites from Point Conception to Bodega Bay, including eight in the Monterey Bay National Marine Sanctuary.
In 2001 PISCO reported on the pattern of mass mortality
of the intertidal black abalone (Haliotis cracherodii) along the west coast of North America. Once the largest and arguably most important herbivore in intertidal systems along much of the west coast of the United States, the black abalone has experienced mass mortalities along California’s coast since the mid-1980s. Mortality is due to infection by a pathogen that leads to a fatal wasting disease called “withering syndrome,” in which the abalone’s foot shrinks until it can no longer adhere to the substratum. The general pattern of mortality, once die-offs start, is that within a few months to a year the population decreases by more than 90 percent, with a few remnant individuals remaining healthy and persisting. Since the early 1990s the disease has migrated sequentially northwards along the coast of California. By 2001 the documented spread of population crashes due to withering syndrome extended to the southern boundary of the sanctuary. At that time the only extant large and healthy populations of black abalone resided in the sanctuary, and this is still the case.
Our monitoring has continued, and through the spring of 2003 black abalone populations throughout the sanctuary remained stable. Importantly, we continued to see recruitment of juvenile abalone at many of our sanctuary sites. Given that the last great onslaught of the disease happened in 1998, we were beginning to think that perhaps the northern populations might not be affected. Since movement of population crashes has been associated with warm water, we hypothesized that water temperatures from Cambria north may not be conducive to population crashes seen to the south. However, we may have to rethink this hypothesis. We have finished about half of our fall surveys and have noted population declines at all of the southern sanctuary sites. This has never happened before.
Whether this represents the beginning of a renewed spread of population crashes due to “withering syndrome” remains
to be seen. However, the declines clearly point to the need
for ongoing monitoring. For more information on the PISCO project, please visit www.piscoweb.org.
* Much of this work started prior to PISCO’s founding.
Other funding sources for this research include the Natural Sciences and Engineering Research Council of Canada, the Mineral Management Service, the UC Toxics Substances Research and Teaching Program, and the National Science Foundation.
– Peter Raimondi1 and Lydia Bergen2
1Department of Ecology and Evolutionary Biology,
University of California Santa Cruz
2Partnership for Interdisciplinary Studies of Coastal Oceans,
University of California Santa Cruz