Research Technical Reports: Biodiversity of the Rocky Intertidal in the Monterey Bay National Marine Sanctuary: A 24-year Comparison

Cite As:
Pearse, John. Biodiversity of the Rocky Intertidal Zone in the Monterey Bay National Marine Sanctuary: A 24-year Comparison. California Sea Grant: Report of Completed Projects 1994-97. Publication No. R-044:57-60.

Ten rocky intertidal platforms along the coast of San Mateo and Santa Cruz counties were surveyed for biotic richness in 1971-73 by students of the University of California, Santa Cruz (UCSC), with support from California Sea Grant and the Association of Monterey Bay Area Governments. The data gathered provided a baseline that could be used for evaluating future changes. In 1996-97, UCSC students re-surveyed these 10 sites with support from California Sea Grant and the Monterey Bay National Marine Sanctuary. The data collected were compared with earlier data to access how the biota on this coast had changed over the past 24 years, after experiencing droughts, floods, a major El Nino, a severe earthquake, and increasing human distubance.

The sites were chosen to span a range from areas heavily impacted by humans within Monterey Bay to more remote areas on the open coast of southern San Mateo County (Fig. 1). A small domestic sewer outfall occurred intertidally at Soquel until 1976, and another occurred just offshore at Almar Street until 1988. Clamming continues to be popular at Point Santa Cruz, and Natural Bridges is used extensively for tidepooling excursions. On the other hand Pigeon Point and the Ano Nuevo sites are difficult to access; the Ano Nuevo area is also protected from human activities, as the elephant seal population increases there.

Each site was surveyed at low tide by teams of 20-30 students on two days during the Spring quarters of 1996 and 1997 and on one day during the Fall quarter of 1996. This regime was more focused than done in 1971-73 when smaller groups of students visited the sites for 7 successive quarters (Fall 1971-Spring 1973). Extensive surveys were made of most groups of macroscopic algae and invertebrates that could be found without destroying the habitat; fishes were also sampled in 1996-97, but not in the 1970s.

Specimens that could not be identified in the field were brought back to the lab, identified, and preserved for documentation. Vouchers of most invertebrate species found in the 1970s were deposited in the collections of the California Academy of Sciences; these were used for verification of identification in comparison with species collected in the 1990s. Professional consultants were brought in to help with particularly difficult taxa: algae (Kathy Ann Miller), sponges (Welton Lee), and bryozoans (Judith Winston).

In addition to the species richness surveys, quantitative surveys were done at 5 of the 10 sites beginning in the early 1970s and continued intermittently to the present (Fig. 1). Relatively flat uniform areas covered with characteristic, visually-dominant species (mussels, anemones, rockweeds, surfgrasses) were selected and served as large permanent plots that could be randomly sampled using 50x50 cm square quadrats. Species richness was similar between 1971-73 and 1996-97 for both algae and invertebrates (Fig. 2). Nearly the same number of species of algae were found at all the sites, reflecting the thorough surveys done by experienced workers in both surveys. However, an average of 30% more species of invertebrates were found at each site in 1990s than in the 1970s, probably due to experience gained by the PI during the intervening years. The Ano Nuevo sites were noted to be particularly rich in number of invertebrate species in the 1970s, which Pearse (1981) attributed to enrichment by the growing seal rookeries there. On the other hand, the increase in species numbers at the Ano Nuevo sites in the 1990s was less than expected, possibly because the number of pinnipeds in the rookeries had reached detrimental levels. Higher than expected numbers of invertebrate species were notable at the relatively remote and exposed sites at Pigeon Point and the heavily used, more protected sites at Point Santa Cruz and Soquel Point within Monterey Bay. The increase at Soquel Point, at least, almost certainly reflects a response to the termination of the sewer outfall there in 1976.

The visually dominant species also remained stable at each of the sites, as documented both from photographic and quantitative sampling data (except Soquel Point, where surfgrasses eventually returned after the sewer discharge was terminated in 1976.) Mussel beds continue to dominate platforms at Almar Street, Natural Bridges, and Davenport Landing (Fig. 3), anemone beds dominate another large portion of the Davenport Landing site, and mixed red algal cover predominates at Ano Nuevo, Pigeon Point, and Point Santa Cruz. The Scott Creek site is unusual in having a very mixed cover of visual dominants, with beds of mussels, anemones, and red algae, but that mosaic pattern also has remained unchanged over the past 24 years.

Similarity among the sites with respect to shared species showed a similar pattern between 1971-73 and 1996-97 (Fig. 4). The San Mateo sites at Pigeon Point and Ano Nuevo remained distinct and separate from the sites on Santa Cruz coastline. Such similarity suggests long-term, site-specific stability within these different assemblages. On the other hand, the Soquel Point site, which placed outside all the other sites in the 1970s, clustered with Point Santa Cruz, the other site within Monterey Bay, in the 1990s; as noted with the species richness data, this change almost certainly reflects the recovery from the sewage discharge at Soquel Point.

Despite the apparent stability of these rocky intertidal platforms, there was considerable flux in species composition at all the sites. About two thirds of the algal species and half of the invertebrate species found at each site were present in both the early 1970s and the mid 1990s (Fig. 5). Many of the species were relatively rare and were only found at one or two sites during the entire surveys, and at different sites during the two periods. Others were so rare that they were only found once or twice anywhere. The Ano Nuevo sites contained an exceptionally high proportion of rare species of invertebrates, which partially accounts for their high species richness. These results indicate that thorough, repeated surveys of a site are needed before its full species richness can be approached or used for comparison with other times or sites.

Species turnover between the two time periods was chaotic, without much evident pattern. Increases in invertebrate species numbers occurred mainly at Pigeon Point, Point Santa Cruz, and Soquel Point (see Fig. 2); the change at the Soquel Point site reflected recovery from the termination of the intertidal sewage outfall there in 1974. We have not been able to detect an underlying pattern of particular classes of species that have changed. Among the invertebrates, pproximately 28% of the species have the center of their distribution south of Monterey Bay, 15% have the center of their distribution north of Monterey Bay, while 57% appear to have broad coast-wide distributions. This pattern held for both time periods, even for sites that increased in species richness. There was little evidence of a shift in species composition over the past 24 years that might reflect global warming, as indicated by a 70-year comparison of a site in southern Monterey Bay (Barry et al., 1995).

These surveys show that there is considerable flux in species composition, both spatially and temporally, in the rocky intertidal biota of southern San Mateo and Santa Cruz counties. Nevertheless, there has been a remarkable stability over the past two-plus decades, and there is no evidence of degradation or deterioration despite increasingly heavy use by people.

The data collected in these surveys are still being analysed. Moreover, they are being transferred to an electronic data base to be maintained by the California Academy of Sciences for accessibility to future workers.

Cooperating Organizations

California Academy of Sciences, San Francisco, California
Monterey Bay National Marine Sanctuary, Monterey, California

References

Barry, J.P., C.H. Baxter, R.D. Sagarin, and S.E. Gilman. 1995. Climate-related, long-term faunal changes in a California rocky intertidal community. Science 267:672-675.

Pearse, J.S. 1981. Intertidal invertebrates. In The Natural History of Ano Nuevo. B.J. Le Boeuf and S. Kaza, eds., Boxwood, Pacific Grove.

Lectures

Watson, L.*, E. Danner, C. Zabin, and J. Pearse. 24-year Comparsion of the Rocky Intertidal of Central California. Annual Meeting of the Western Society of Naturalists, La Paz, Mexico, January 1997.

Pearse, J., E. Danner, L. Watson, and C. Zabin. Stability and Flux in the Rocky Intertidal (poster). Annual Research Symposium of the Monterey Bay National Marine Sanctuary, Santa Cruz, California, March 1997. (received symposium outstanding poster award)

Danner, E.*, L. Watson, C. Zabin, and J. Pearse. Stability and Flux in the Rocky Intertidal of Central California: A 24-year Comparison. Symposium for Marine Conservation Biology, Victoria, Canada, June 1997.

Pearse, J. Stability and Flux in the Rocky Intertidal. Friends of the Moss Landing Marine Laboratories. Moss Landing, California, July 1997.

Pearse, J. Stability and Flux in the Rocky Intertidal of Central California: A 24-year Comparison. Smithsonian Tropical Research Institute, Panama City, Panama. September, 1997.

Pearse, J. The Rocky Intertidal of Central California: Good News. University of California, Santa Cruz, California. October 1997.

Pearse, J., The Rocky Intertidal of Central California: Good News. Monterey Bat Aquarium Research Institute, Moss Landing, California. November 1997.

Pearse, J.*, E. Danner, L. Watson, and C. Zabin. Recovery of a Rocky Intertidal after Closure of a Sewage Discharge. Annual Meeting of the Western Society of Naturalists, Monterey, California, December 1997.