Biodiversity of rocky intertidal of northern Monterey Bay: A 24-year comparison
- John Pearse
University of California, Santa Cruz
End Date: August 31, 1997
Species richness of 10 sites between Pigeon Point and Soquel Point were surveyed by students of the University of California, Santa Cruz in 1971-1973 and again in 1996-1997. The sites were Pigeon Point (north and south), Ano Nuevo Point, Ano Nuevo Cove, Scott Creek, Davenport Landing, Natural Bridges, Almar Street, Point Santa Cruz, and Soquel Point. Teams of 20-30 students visited each of the 10 sites each quarter and enumerated the species found (algae and invertebrates; fishes in 1996-1997 only); specimens that could not be identified were brought back to the lab for microscopic examination, and some were sent to experts for verification. Vouchers of the invertebrates found in 1971-73 were deposited with the California Academy of Sciences.
The total number of species found at each site was remarkably similar between the two survey periods. More invertebrates were found at all sites in 1996-97 than in the 1970s, probably because of increased experience by the principal investigator. Signficantly more species were found at Soquel Point and Point Santa Cruz in the 1990s than the 1970s, probably because of improved water quality (an intertidal domestic sewage outfall at Soquel Point was discontinued in 1976). In contrast, there was significantly fewer species at the Ano Nuevo sites (the richest in terms of invertebrates) in the 1990s than the 1970s, probably because of the marked increase of pinnipeds there over that time period.
The visually dominant species at each site remained the same between the two study periods with no obvious change. Quantitative studies were done at 5 sites (Pigeon Point south, Davenport Landing, Natural Bridges, Almar Street, and Soquel Point) by counting abundances of selected species in randomly placed quarter-meter quadrats within large plots on relatively flat, uniform areas. These were done irregularly over the time between the early 1970s and 1996-97; some are being continued by the MBNMS's LiMPETS program. Little change has been detected at each site: red algae dominate the Pigeon Point South site and mussels the Davenport Landing, Natural Bridges, and Almar sites. A plot on a bed of aggregrated sea anemones also remained unchanged at the Davenport Landing site. After the sewage discharge was terminated at the Soquel Point site, surfgrass slowly returned to once again dominate that site.
Despite the overall lack of change at most sites in dominant species present and species richness, species composition differed both among the sites and between the two study periods at all the sites. There was considerable flux in species composition, both spatially and temporally, probably because most of the species recorded are relatively rare and inconspicuous so that the chance of finding individual species at any one site or time period is low. There was no evidence of an increase in southern species, or decrease in northern species, that might reflect global warming.
The main conclusion from these surveys is that there was remarkedly little difference between the 24 years separating the two study periods, and no evidence was found of degradation or deterioration despite the increasingly heavy use at most sites by people (Ano Nuevo being the exception because people are now not permitted free access to the area).
This project was supported by California Sea Grant, the Association of Monterey Bay Area Governments (1970s), and the Monterey Bay National Marine Sanctuary (1990s). The results are summarized in the Report of Completed Projects, 1994-97, California Sea Grant College System.
Summary to DateThe main conclusion from these surveys is that there was remarkedly little difference between the 24 years separating the two study periods, and no evidence was found of degradation or deterioration despite the increasingly heavy use at most sites by people.
- species richness and composition
Study Methods(1) Teams of trained undergraduate students searched each site and enumerated all species found; those not identified in the field were brought back to the lab to be keyed out or to send to specialists.
(2) Students counted the abundance of selected species in quarter-meter quadrats randomly placed within large permanent plots.
Figures and Images
Figure 1. Dr. John Pearse, professor emeritus at UC Santa Cruz, walks the intertidal study site of Soquel Point.
Figure 2. Current and past undergraduate and graduate students assist Dr. Pearse with quantitative sampling at intertidal sites in central California.
Figure 3. This study site at Soquel Point used to have an active sewer discharge. Pearse and his students began monitoring this site just prior to cessation of discharge in the early 1970s.
- Comprehensive species list (2008)A comprehensive species list compiled over the 24-yr period of this intertidal study.
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