National Park Service

State of the Park Reports

State of the Park Report for Cabrillo National Monument

Resource Brief – Rocky Intertidal Community

"The appearance of the Cabrillo National Monument tide pool area has changed dramatically since the early 1960s. At that time, mussels and sea stars visually dominated the space. Everywhere you looked, you saw vast expanses of mussel beds stretching from the water up rock and cliff faces at least six feet, fringed on the lower edge with splashes of bright orange and purple color of the Pisaster sea stars. Also green and black abalone and lobster were common elements of the community."(Gary Davis, Visiting Chief Scientist, National Park Service, retired)

Cabrillo Tidepools in 1962 Cabrillo Tidepools in 2005

Photographs of mussel beds in the Cabrillo rocky intertidal community area in 1962 (left), and the same location in 2005 (right).

In 1990, alarmed at what appeared to be significant declines in rocky intertidal flora and fauna, NPS scientists began a monitoring program focused on 13 species playing key ecological roles in the environment. After five years of monitoring, 7 of those 13 species had declined, 5 had remained stable, and only 1 had increased. Two of those species, black abalone and ochre seastars, had disappeared from Cabrillo entirely, even though they were once very abundant.

To mitigate these impacts, Cabrillo established the Tidepool Protection, Education, and Restoration Program (TPERP), which had three elements. First, and arguably most important, an increase in staff and volunteer presence was devoted to the rocky intertidal area of the park. Currently, TPERP consists primarily of volunteers who do their best to interpret the intertidal flora and fauna to park visitors, but also to remind them of Cabrillo's no-collecting rules and that the touching of marine organisms needs to be done gently, as if touching one's own eyeball. Second, three management zones were established, and one-third of the rocky intertidal zone at Cabrillo was closed to the public in 1996, to allow recovery and to serve as an ecological reference area for the remainder of the park. This ecological reference area has been extremely important as a scientific baseline area and for learning about and informing visitors, school children, and others about the effects of human activity within the rocky intertidal community and the importance of careful management. Third, the park made a commitment to long-term monitoring in perpetuity of the rocky intertidal resources. The protocols for this long-term monitoring are standardized from Alaska through Baja California, so that analyses of the data can determine if changes found at Cabrillo are local to Cabrillo, regional (coastal California south of Point Conception), or widespread.

TPERP is regarded as a success story for Cabrillo, and rightly so. Peer-reviewed scientific studies have shown that the sizes of several invertebrates are larger at Cabrillo than anywhere else in Southern California, and that the TPERP intertidal volunteers play a huge role in protecting the intertidal resources at Cabrillo. Surf grass, which provides food and shelter for many other species, remains abundant where it was found in 1990, and has increased in cover in transects where boa kelp dominated in 1990. Recently boa kelp has been increasing. Even so, the Cabrillo rocky intertidal is not what it used to be. Today's visitor experiences something far different from visitors of 30 years ago. Black abalone and ochre seastars remain extinct within the park. Abalone were heavily overfished, and both seastars and abalone succumbed to disease in the 1970s and 1980s, respectively (Richards and Davis 1993, Alstatt et al. 1996, Raimondi et al. 2002). Mussels, the most ecologically dominant organism in the west coast rocky intertidal community, crashed in the late 1980s and early 1990s along the southern California coast. While their abundance recovered in two or three years over much of that area, the recovery in Cabrillo has been much slower, with mussels reappearing only sparsely in management zone 1 in 1995. Recent analyses of the last 20 years of monitoring data revealed a decline in the size of owl limpets for unknown reasons. This decline is of special concern because owl limpets change from juveniles to males to females as they grow larger, so loss of the largest individuals skews the sex ratio and has a large impact on egg production. Silvetia (rockweed) is declining at Cabrillo but less so than at other areas in southern California (Becker 2006, Pister et al. in prep, Yap, personal communication).

Comparisons of species composition and abundance between Cabrillo and other Southern California rocky intertidal areas have been used to quantify the impacts of trampling, collecting and adjacent land development. In many ways the Cabrillo rocky intertidal is in better shape than most other places in the region. However, the gradual changes documented in the Cabrillo rocky intertidal community illustrate the concept of "shifting baselines". What are considered "normal" or good conditions now are very different than what was here decades ago. The current conditions at Cabrillo do not reflect the historical conditions at Cabrillo or at those other locations.

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Last Updated: October 18, 2016 Contact Webmaster