Inventory of Rocky Intertidal Resources in San Diego County

Principal Investigator:

John EngleUniversity of California, Santa Barbara

This project was initiated in November 1996 to extend the period of monitoring of rocky intertidal resources along the Point Loma Peninsula in San Diego County. Previous surveys supported by the Cabrillo National Monument and the U.S. Navy were conducted during the period 1990-1995. This work is part of a coordinated effort to establish and monitor a regional network of rocky shore stations. Other programs have maintained long-term monitoring sites at the Channel Islands and along the mainland of San Luis Obispo, Santa Barbara, Ventura, and Los Angeles Counties. Long-term monitoring of rocky shore biota will aid understanding of natural variability in key species populations, and provide important baseline information should these resources be damaged by an oil spill or other impact.

As originally proposed, the project provided for 15 months of rocky intertidal sampling in San Diego, including fall 1996 and spring 1997 monitoring surveys at five sites along the coast of Point Loma. With cooperative assistance from the National Park Service (Cabrillo National Monument) and the U.S. Navy, it became possible to arrange a no-cost extension of the project to include sampling in fall 1997 and spring 1998. Three of the intertidal sites (Cabrillo I, II, III) are located in the Cabrillo National Monument, along a gradient of visitor use extending from the sole shore access. The other two sites (Navy South, Navy North) are located farther upcoast along the relatively isolated Navy property. Using the same procedures developed for the other regional network stations, abundance data on 13 key algal and invertebrate species at the rocky intertidal sites are collected within replicated permanent plots, including photoquadrats, circular plots, and line transects.

Progress and Findings:
Fall 1997 field sampling of the 170 fixed plots at the 5 sites took place during a daytime low-tide series on October 14-18; spring 1998 sampling occurred during February 22-27 and March 24-27. Both surveys were carried out in cooperation with the National Park Service and U.S. Navy. After each field trip, the photographic slides were scored in the laboratory to determine percentage cover of key species, and all sampling data were entered in the computer.

The spring 1998 sample represents the 17th semi-annual survey of the rocky intertidal resources at the 3 sites in the Cabrillo National Monument since monitoring began in 1990. It is the 6th survey of the two sites on the Navy shore since 1995. Information from all surveys prior to fall 1996 have been presented in separate reports for the National Park Service (Cabrillo I, II, III) and U.S. Navy (Navy South, Navy North).

The final report for this project will be submitted by September 30, 1998. The report will contain data tables and figures detailing the monitoring results, including summary data from all prior surveys. Patterns and trends in the data for the four seasonal surveys from fall 1996 through spring 1998 will be discussed and compared with previous surveys at the 5 Point Loma stations. The study findings to date are summarized below:

Of the 13 key species monitored at the 3 Cabrillo National Monument rocky intertidal sites, 2 species (black abalone, ochre seastar) were not found and 2 species (sargassum weed, aggregating anemone) occurred only in minor amounts. Though once common on Point Loma shores, no black abalone and only 1 ochre seastar have been found during searches of the entire study sites since 1990. Sargassum weed and aggregating anemones occurred commonly at the monitoring stations, but were not primarily targeted in fixed plots or transects. Of the 9 other target species, 5 (pink thatched barnacle, goose barnacle, mussel, red turf, boa kelp) remained essentially unchanged, 2 (acorn barnacle, owl limpet) declined slightly, and 2 (rockweed, surfgrass) declined moderately. Overall, no key species increased in abundance from fall 1996 to spring 1998. Trends generally were the same for species monitored at the 2 Navy sites farther north on Point Loma except that acorn barnacle and surfgrass declines here were less, and owl limpet numbers increased substantially, primarily due to increased numbers of small limpets found at Navy North.

Trends in species abundances at the Cabrillo National Monument sites during previous monitoring from 1990 to 1995 included major increases in surfgrass, minor declines in goose barnacles and owl limpets, and greatly reduced thatched barnacles, mussels, and boa kelp. Since 1995, goose barnacles, thatched barnacles, and boa kelp have not recovered to prior levels. Owl limpet numbers generally have increased to former amounts. Mussels have increased substantially in Cabrillo I to the highest levels since monitoring began, but Cabrillo II and III plots remain nearly devoid of mussels.

Since 1995, acorn barnacle cover declined slightly, and rockweed and surfgrass showed moderate losses. These decreases in abundance occurred after spring 1997, during the strong El Niņo event. The El Niņo included above normal water temperatures, heavy rainfall, and large storm swells. Both the fall 1997 and spring 1998 samplings took place after periods of heavy surf. Large accumulations of kelp wrack and drift debris were observed on the shore in fall 1997. More than usual amounts of overturned rocks, cobble scoured surfaces, breakouts of sedimentary bedrock slabs, and damaged plot/transect markers were found during both of the latter surveys. Disturbance from El Niņo storms likely "thinned out" acorn barnacles, rockweed, and surfgrass; however, other key species coverage appeared largely unaffected. Rocky intertidal monitoring sites established in fall 1997 for the Navy at Cardiff and Scripps Reefs in central San Diego County sustained greater storm damage than at Point Loma, including losses of rockweed, surfgrass, acorn barnacles, sand castle worms, goose barnacles, and mussels.

In addition to El Niņo related changes, most key species showed periodic, irregular, or multi-year abundance patterns. For example, minor seasonal cycles generally were evident for 5 key species. Rockweed and surfgrass tended to be less abundant in spring periods, while sargassum weed, red algal turf, and goose barnacles often had lower cover in fall surveys. The cover of acorn barnacles was quite variable (likely reflecting irregular recruitment events), while that for red turf exhibited considerable stability over the years. Surfgrass replaced boa kelp as the dominant species in the boa kelp transects. Owl limpets and goose barnacles on layered sedimentary rocks occasionally disappeared when sections of the soft rock broke out. Mussel recruitment eventually enhanced the mussel plots at the more exposed Cabrillo I site, while mussel losses in Cabrillo II and III have not been compensated for by new settlement. These examples of dynamic patterns and trends in Point Loma key species populations demonstrate the importance of long-term monitoring in assessing the changing "baseline" condition of intertidal resources.

Table 1. Field Activities for the San Diego County Rocky Intertidal Monitoring Project.
Fall 1997October 12Cardiff ReefEstablish rocky intertidal monitoring site
October 13Scripps ReefEstablish rocky intertidal monitoring site
October 14Navy South, Pt. LomaRocky intertidal fall sample
October 15Navy North, Pt. LomaRocky intertidal fall sample
October 16Cardiff ReefSite establishment; fall sample
October 17Scripps ReefSite establishment; fall sample
October 18Cardiff ReefSite establishment; fall sample
Spring 1998February 23Navy South, Pt. LomaRocky intertidal spring sampling
February 25Scripps ReefRocky intertidal spring sampling
February 26Cardiff ReefRocky intertidal spring sampling
February 27Navy North, Pt. LomaRocky intertidal spring sampling

Table 2. Personnel Participating in San Diego Rocky Intertidal Surveys.
ParticipantsAffiliationStatusFall 97Spring 98
Jack EngleUniversity of California, Santa BarbaraEmployeeXX
Dan MartinUniversity of California, Santa BarbaraEmployeeXX
Dave HubbardUniversity of California, Santa BarbaraEmployeeX
Jessie AltstattUniversity of California, Santa BarbaraEmployeeX
Cindy TaylorScripps Institution of OceanographyEmployeeX
Alan AnzakUnited States NavyEmployeeX
Cleave BerdzarUnited States NavyEmployeeX
Erik SteenblockUnited States NavyEmployeeX
Gary DavisChannel Islands National ParkAdvisorX
Anita BurkettCabrillo National MonumentVolunteerX
Andrea ComptonCabrillo National MonumentVolunteerX
Bob GladdenSan Diego Underwater Photographic SocietyVolunteerXX
Richard HerrmannSan Diego Underwater Photographic SocietyVolunteerX
Robin LewisCalifornia Department of Fish and GameVolunteerX
Greg MorrisSan Diego State UniversityVolunteerX
Samantha WeberCabrillo National MonumentVolunteerX
Dave YoungUniversity of California, San DiegoVolunteerXX