Geology

Tidepools

Windows to the Sea

On the western side of Point Loma lies the rocky intertidal zone, a window into the ocean ecosystem that lies along of San Diego's coast. During periods of low tide, pools form along this shore in rocky depressions. In them you may see flowery anemones, elusive octopi, spongy deadman's fingers, and a myriad of other creatures. The tidepools are a wonderful discovery zone, but be careful if you visit. The intertidal area is a very sensitive ecosystem. Few animals in this ecosystem can harm humans, but many animals are sensitive, and can even be killed, when handled or just touched by humans. Ask a ranger or volunteer how you can best explore the tidepools without harming them.

Ranger walks are available during most low tides and a slide program is shown daily at the park visitor center. Low tides during convenient daylight hours are most common in the winter during full and new moons. Check a tide chart or give us a call at (619) 557-5450, extension 0, before you visit for the best time to explore the tidepools.

Inhabiting the subtidal zone, outside of Cabrillo National Monument's boundaries, is the kelp forest. This is a habitat where large marine plants (kelp) form tall "trees" making an underwater forest. The kelp helps support life in the deeper ocean. These plants are fed upon by sea urchins and abalone. Large fish and mammals also inhabit the kelp forest, eating the sea urchins and abalone.

The Cautious Visitor

Please keep in mind that algae-covered rocks are wet and slippery. Because you can expect to get wet, wear shoes with good traction and wear clothes you don't mind getting wet. You will be more relaxed, have more fun, and be safer if you don't have to worry about your good shoes or pants getting doused by a stray wave.

The Plight of the Owl Limpet

The tidepools at Cabrillo National Monument are currently being studied to assess the impact human visitors have on them. Initial results seem to indicate that humans are contributing substantially to the decline of many species. The National Park Service, however, believes that we are capable of resolving the problems that face the intertidal animal and plant life so that we may - hopefully - undo some of the damage and help these species survive.

For example, consider the plight of the owl limpet...

Owl limpets are still fairly common on the rocks of Cabrillo's tidepools. But so too were abalone at one time. Then people discovered how good abalone tastes and they began disappearing. Now it is nearly impossible to find even a small abalone at Cabrillo. Like the abalone before them, owl limpets today may be in danger of disappearing simply because they taste good.

In the 1970s, owl limpets that lived in Cabrillo's tidepools were abundant and averaged 50.25mm across in size. Meanwhile, only four miles up the coast at Sunset Cliffs, owl limpets at that time averaged only 30.61mm. The older, larger owl limpets at Sunset Cliffs were apparently being gathered for human consumption. At Cabrillo National Monument, however, no collecting of any kind is allowed, so the animals are able to grow older and bigger.

Here is a curious and worrisome twist: owl limpets are hermaphroditic - in other words, they are both male and female during their life span. They are male when they are young (and small), and female when they get older (and larger). This is important because it may be that owl limpets are not growing large enough to fulfill the female role of reproduction at Sunset Cliffs. At Cabrillo, however, the tidepools are closely monitored and owl limpets are able to grow to a large, female, size.

It is possible that protected areas like Cabrillo's tidepools serve an important function as breeding grounds for owl limpets and other commercially important species in the area. Most limpets hatch from eggs into a larval form that drifts with the ocean's currents to their eventual homes. Perhaps many owl limpets that spawn (hatch) at Cabrillo are swimming away and replenishing other areas of the coastline with young owl limpets. If this speculation is the case, then it is very important that we protect and preserve areas like the Cabrillo tidepools.

A recent study, however, suggests that even the Cabrillo owl limpet population is in danger. Between 1990 and 1995, owl limpet numbers declined an overall 23%, and individual animals were found to average only 45mm in length (5.25mm less than they were twenty years ago). Park Rangers sometimes discover people collecting illegally in the park, and are worried that this poaching may be causing the decline. The park has increased the presence of Park Rangers and Volunteers in the tidepools, and Rangers take a strong stance on enforcing the "No Collecting" policies in the park.

We hope you will visit and discover the Cabrillo tidepools. If you do, please remember to be careful and be mindful of the rules, so that we may preserve the diversity of life that exists here.

Coastal Sage Scrub and Southern Maritime Chaparral Communities

Communities

Because Cabrillo National Monument is located on a peninsula, its natural features encompass terrestrial and marine ecosystems. From the 422-foot ridge of the peninsula down to the San Diego Bay on the east and the Pacific Ocean on the west, one can see the scrubland habitat. The scrubland on Point Loma includes four community types: southern coastal bluff scrub, maritime succulent scrub, Diegan coastal sage scrub, and southern maritime chaparral. These communities are home to a variety of plant species such as snake cholla, prickly pear cactus, Mojave yucca, Shaw's agave, California coast poppy, Indian paintbrush, California buckwheat, California sagebrush, and lemonadeberry. These plant communities make up the coastal Mediterranean ecosystem which supports a variety of southern California animal species such as velvet ants, scorpions, shrews, mice, lizards, snakes, red-tailed hawks, foxes, and coyotes.

A Summary of Coastal Sage Scrub Habitat

For millennia, the southern California coast, foothills, and western slopes have been home to scrub and chaparral. Unlike plant and animal relatives found in the mountains and deserts, coastal sage scrub species have adapted to an ecosystem that rarely freezes in the winter and only occasionally experiences temperatures over 90 degrees F during the dry California summer.

Southern California's coastline, once covered by coastal sage scrub, is now largely developed. Only scattered pockets of this endangered habitat remain. One such pocket is the Point Loma Ecological Conservation Area, an area of 840 acres protected under the joint management of the U.S. Navy, Cabrillo National Monument, U.S. Coast Guard, Department of Veterans Affairs, and City of San Diego Wastewater Treatment Plant.

The Bayside Trail, a 2½-mile self-guided round trip, is located in Cabrillo National Monument. This trail offers a good way to enjoy this special habitat. A variety of plants, small reptiles, and mammals - as well as a number of indigenous and migrating birds - reside here. During the dry summer, many of the plants may appear to be dead but they are actually dormant and will become green and vibrant again with the winter rains. Spring wildflowers are a special treat from February until May. Park Rangers and Volunteers occasionally give coastal sage scrub walks. Please check at the visitor center or call (619) 557-5450, extension 0, prior to your visit.

The Ecosystem During Cabrillo's Visit

Native plants found in the park today are part of the coastal sage scrub community that Cabrillo encountered when he landed here in 1542. Then, as now, the community was comprised of an association of woody shrubs ranging in height from one to ten feet. It was typified by California sagebrush, white and black sage, California buckwheat, toyon, and lemonadeberry. Plants as well as animals have adapted to arid coastal climates.

Among the animals Cabrillo and his crew may have seen during his visit are mammals such as rabbits, squirrels, foxes and coyotes, a variety of lizards and snakes, and birds such as the scrub jay, red-tailed hawks, quail, and others.

The Evolution of Coastal Sage Scrub Ecosystem

This sage scrub environment evolved within the Mediterranean climate. This term refers to climate belts found in both the northern and southern hemispheres on the western coastline of continents, approximately between 30 and 40 degrees latitude. Mediterranean climate belts receive an average of 10 to 20 inches of rainfall a year and experience only occasional frosts. These areas typically have winter rains and dry warm summers with a fairly constant temperature.

The coastal sage scrub and chaparral associated with Mediterranean climates evolved in response to climatic changes beginning about 14 million years ago. In these latitudes, average rainfall decreased from about 80 inches or more per year in the Eocene Epoch to only about 12 inches by the middle of the Miocene Epoch.

Plant Adaptations

Coastal sage scrub plants can store moisture and reduce moisture loss during the prolonged hot, dry months between April and October. The plants either conserve water by specialized leaf structures or through dormancy. Tough, leathery, wax-covered leaves, like those of the lemonadeberry shrub, prevent water from escaping through leaf pores. Minute white hairs keep leaf temperatures down by reflecting sunlight. They also reduce moisture loss by slowing dry winds. Some leaves are so reduced in size that they appear as spines, as on cacti. Other plants simply drop their leaves during summer months.

Other species, especially the flowering ones, will dry up and go dormant by middle summer. Although they appear to be inactive during this time, growth is still occurring. Root systems can be extensive, sometimes exceeding 30 feet. The roots anchor the plants, hold soil in place and reduce runoff during winter and spring rains.

The community is both drought and fire-adapted. Fire is a healthy and necessary component of their life cycle. Shrubs respond to recurrent fires in several ways. They resprout from both crown and roots, and, often at an early age, produce seeds that are both fire resistant and dependent for germination (growth). Fire creates a healthy plant mosaic of different ages and species. As a result, fire increases the diversity of habitats.

While in the park, look for changes in the species which dominate different sections of the trailside. Even within a small area, subtle differences, such as exposure to light and moisture caused by elevations and slope changes, will favor some plants at the expense of others.

The Cycle of Life

Among the plants live a variety of animal species, some rare. Within the ecosystem, there are levels of animal and plant life. The bottom level includes decomposers such as fungi, bacteria and worms. They live off decaying material and waste and return organic compounds to the soil--providing nutrients for plants. Herbivores, such as rabbits and squirrels, live off the plants. They, in turn, are eaten by carnivores (meat eaters), such as foxes, hawks, and owls. When these plants and animals die, the decomposers start the cycle again.

Invasion and Preservation

Originally the dominant ecosystem, the coastal sage scrub community now only exists in remnant San Diego County habitats, due to heavy growth and development in the region. The small native plant communities that do remain in canyons and other sites, like Point Loma, are fragmented and invaded by exotics (non-native vegetation and animals). As a result of this highly fragmented habitat in urban San Diego County, it is not uncommon to find coyotes wandering residential streets, or raccoons foraging through neighborhoods.

The National Park Service is committed to preserving and protecting native communities wherever they occur within National Park System boundaries. Fortunately, CabrilloNational Monument retains its native community. Using National Park Service guidelines, we are gradually removing exotics and are reintroducing native plants. We also perform scientific studies to learn more about this unique and shrinking ecosystem.

We ask you to help preserve this precious community by not picking, removing, or otherwise disturbing any plant or animal life in the Monument.

Other National Park Service sites with Coast Sage Scrub habitat:

• Santa Monica Mountains National Recreation Area
• Channel Islands National Park

Environmental Factors

An "Island" in the Big City

Cabrillo National Monument sits at the end of a naturally beautiful promontory affected by numerous environmental factors and influenced by a nearby city and port. The monument contains 160 acres at the tip of the Point Loma peninsula, which reaches an elevation of 422 feet. It is bordered to the west by the Pacific Ocean, on the east and south by San Diego Bay, and on the north by an urban environment. The portion of the peninsula that is not owned by the National Park Service is divided among the U.S. Navy, U.S. Coast Guard, the City of San Diego, and the U.S. Department of Veterans Affairs. All of these landowners have collaborated and established the Point Loma Ecological Conservation Area (PLECA), which covers 662 acres, in order to enable management of the natural resources on the entire peninsula.

Weather data is recorded for San Diego at Lindbergh Field (the airport), which is directly across the bay from the monument. The average annual temperature is 64 degrees and the average annual rainfall is a scant 9.5 inches. Rainfall is concentrated in the winter, from November to April, but the amount can drastically change year to year, from 3.4 inches to 19.4 inches. This variability in rainfall causes certain types of plants to thrive one year and barely survive another. Nature makes up for this lack of rain when cold air from the ocean meets the balmy air on the land and dense fogs roll in. The fog adds moisture to allow species requiring more water to coexist with the desert plants and animals. The ocean also keeps air temperatures mild year-round, which allows heat-loving cactus to grow next to evergreen shrubs common in cooler climates, salamanders to walk past sunning desert snakes, and mosses to grow in the cool shade, a stone's throw from where parched lichen cling to dry, hot boulders.

The peninsula is comparable to an island because of the aquatic borders and the urban landscape to its north. Sources of factors that continually influence the monument and the PLECA are the North Island Naval Air Station across the bay, the San Diego airport seven miles to the northeast, and the city of San Diego, an urban environment surrounding the park. Air quality issues include pollution from vehicles which compromise the views from the scenic overlook at the monument's Visitor Center. There are a number of influences on the soundscape, including military and commercial aircraft, the fog horn on the jetty, Coast Guard and Navy activity, vehicular traffic, and operation of the Point Loma Waste Water Treatment Plant. San Diego Bay is a major port of entry, especially for ships traveling north from Mexico. The Navy operates several bases with direct access to San Diego Bay including Naval Base Coronado, Naval Base San Diego, and Naval Base Point Loma (with associated submarine bases). The U.S. Coast Guard also actively uses the bay for daily operations and maneuvers. Water quality is affected by the industries around the bay, and commercial, governmental, private, national, and international ships and boats. Personal watercraft are also used in the bay and are a source of pollution. The City of San Diego operates a Wastewater Treatment Plant north of the monument's intertidal area. This plant treats 180 million gallons per day of sewage and deposits the treated effluent four miles offshore at a depth of 400 feet. In 1992, an accidental leak released effluent along the rocky intertidal coast. There is no current direct discharge, but there is an on-going possibility of a leak.

Non-native species are the biggest threat to the park. These are sometimes called "exotics." Exotics are plants and animals that are not from the monument's coastal sage scrub and marine communities, but have somehow been introduced (either accidentally or intentionally) to the environment and have adapted to it. Exotic species can be detrimental to native species. One example of this is the non-native Argentine ant. These ants have displaced the native ants and have caused major problems for the coast horned lizard population. The coast horned lizard survives on native ants, and does not eat the Argentine ants. In those areas where Argentine ants have established colonies, the coast horned lizard has died off and no longer exists. This has occurred at the park where insufficient number of native ants and a lack of habitat no longer allow the coast horned lizard to exist.

Low Tide - Best Dates and Times

The Best Times for Visiting the Tidepools

Late fall and winter are the optimum times for a visit to the tidepools at Cabrillo National Monument: unlike the summer months, when low tides occur in the middle of the night, the good low tides - including the outstanding negative low tides - in fall and winter occur during daylight hours when the park is open.

Tide Calendars

To see a graphic representation of tide activity, check out the following tide calendars, provided courtesy of Divebums:

Nature's Windows of Opportunity

Of course, the best time to visit the tidepools is as close to the low tide time as possible, but Mother Nature has built in a four-hour window of opportunity for you. A general rule of thumb is that the tidepools can be visited approximately two hours before low tide time (when the tide is receding) and two hours after (when the tide is coming back in). Please keep in mind that the tidepool area closes at 4:30 PM. Be sure to read Tidepooling Tips and Rules to Protect the Tidepools to ensure a safe visit for both you and this fragile ecosystem.