The northward path across the Golden Gate Bridge leads away from the bustle of the Bay Area, past the headlands and rolling hills of Marin, to the windy, wild coastline of Sonoma County. Here, the rocky landscape includes steep sea cliffs, pocket beaches and coves, and sea stacks that rise from the ocean depths just off shore. Enormous surf often pounds the exposed rocky reefs along this stretch of coast, but visitors and marine creatures alike find refuge in the many sheltered coves that dot the shoreline.
One such cove is Gerstle Cove State Marine Reserve (SMR). Encompassed by the land-based Salt Point State Park on one side, and the offshore Salt Point State Marine Conservation Area on the other, Gerstle Cove SMR is one of the smallest of California’s 124 marine protected areas (MPAs), covering only 0.01 square miles. Protected since 1971, it is among the oldest of the no-take MPAs in the state. Gerstle Cove SMR was incorporated into California’s MPA Network in 2010.
During the 1800s, Gerstle Cove was the site of a productive sawmill and rock quarry once owned by Lewis Gerstle, the cove’s namesake. Lumber and slabs of sandstone harvested from the coastal cliffs were loaded onto ships via wire cables anchored to nearshore rocks, transported down to San Francisco, and incorporated into building projects in the booming city. Large bolts and square-shaped scars in the rocks of Gerstle Cove are all that is left as evidence of the area’s economically driven past.
Today, Gerstle Cove SMR and Salt Point State Park are popular destinations for outdoor-lovers visiting the Sonoma coast. A campground and parking lot on the marine terrace just above the cove provide easy access for coastal visitors, recreational divers, kayakers, and the researchers monitoring rocky tide pools in the MPA.
Rocky Intertidal Monitoring at Gerstle Cove SMR
As a researcher and environmental scientist monitoring MPAs for the California Department of Fish and Wildlife, I sometimes collaborate with scientists who are part of the Multi-Agency Rocky Intertidal Network (MARINe). My first visit to Gerstle Cove SMR was on a foggy summer’s morning in 2010 to collect baseline data in the rocky intertidal zone with MARINe scientists, as part of the Statewide MPA Monitoring Program.
You need a number of things to work in the rocky intertidal, but daylight is not necessarily one of them. During the summer months in California the low tides occur very early in the morning, so our alarm clocks sounded wake-up calls long before daybreak. After downing large and very necessary cups of coffee, we arrived at Gerstle Cove, strapped on our headlamps, boots, and weatherproof coveralls to protect us from the elements, and made our way down the trail just as light began to tinge the eastern horizon.
Setting up an intertidal research site is not always straightforward, especially in the foggy, dim morning light. There are many factors to consider. Do the organisms of interest live there? Is there enough space on the rocks to set up monitoring plots? Will researchers be safe from waves while working? We kept these questions in mind as we spread out amongst the boulders to look for potential study plots.
As I made my way closer to the water’s edge, the beam of my headlamp illuminated colorful seaweed, crabs scurrying into cracks away from the sudden influx of light, and red abalone (Haliotis rufescens) hiding in crevices. On the north side of Gerstle Cove, the silhouettes of sea palm (Postelsia palmaeformis), an intertidal kelp, topped the nearshore rocks and became more visible in the growing morning light. We counted each individual sea palm to monitor their population numbers.
Mussel beds (Mytilus californianus) covered a gently sloping rock incline on the south side of Gerstle Cove, a good place to set up rocky intertidal biodiversity surveys. These surveys reveal the number of different species of seaweed and invertebrates that live in the rocky intertidal zone, and how these numbers compare to each other. Owl limpets (Lottia gigantea), red abalone, and sea stars (Pisaster ochraceus) were among the intertidal creatures we counted and measured that foggy morning. We placed permanent markers in areas where we counted organisms, so we could revisit the site in the future during long-term monitoring efforts. Revisiting the same area to collect data over time helps us detect changes in marine ecosystems, both inside and outside of MPAs.
The rocky intertidal monitoring site at Gerstle Cove is one of 164 MARINe monitoring sites across the statewide MPA network. In all, MARINe monitors over 200 rocky intertidal sites from Alaska to Mexico. For more information about other monitoring activities that occur in Gerstle Cove and across the MPA network, visit CDFW’s MPA website and sign up to receive updates about the MPA Management Program.
Learn more about MPAs by diving into the
Exploring California’s Marine Protected Areas series!