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Mandala of the Seasons: Summer
Summer Weather
Summer weather in the Marin Headlands is often a mystery to people who are not used to coastal conditions.
While it will often be hot and sunny further inland or even just on the other side of the hills, the headlands are often shrouded in a soupy blanket of fog. A source of our fog is California's Central Valley, many miles to the east of our coast. It gets quite hot in the Central Valley in the summer due to intense sunshine and long summer days. Air in the Central Valley heats up and rises. This mass of rising air leaves a blank space, or vacuum, that needs to be filled. Air flows in from the ocean in order to fill this space. As this ocean air passes over the cold water right off our coast, it cools down and looses its ability to hold moisture. The extra moisture released from the air clings on to countless tiny particles in the air and forms fog. This fog covers the Marin Headlands, San Francisco, and other parts of the Bay Area for days at a time in the Summer. Besides acting as natural air conditioning, the fog gives the Bay Area its characteristic charm.
Monterey Cypress in the Summer Fog
The coldest Winter I have ever spent was a summer in San Francisco. - Attributed to Mark Twain
Summer Animals
The activity overhead and in the water around the Headlands picks up noticeably when brown pelicans return from their breeding grounds further south.
These impressive birds can have wingspans of up to seven feet long. They are surprisingly graceful as they fly through the air along the coast singly or in formation. Pelicans can also be seen diving head first into the ocean for fish. As they open their mouth underwater, a loose pouch attached to their lower jaw fills up with up to two gallons of water to trap their prey. Even though brown pelicans have a strong visual presence on the coast, they are notably silent as they do not make calls or songs.
These marvelous birds came to the brink of extinction a few decades ago due to the careless use of the pesticide, DDT. The toxic compound made its way through the food chain and accumulated in birds, making their eggshells brittle. The eggs were crushed by their mothers as they sat in their nest. Thanks to the hard work of a generation of environmental advocates, brown pelican numbers have been steadily increasing since the ban on DDT in this country in 1973.
When not flying, brown pelicans can be found resting in large numbers along the banks of Rodeo Lagoon or offshore on the local bird rock
Summer Plants
By summertime, many plants have stopped putting effort into their showy flowers, which serve as bright billboards enticing passing pollinator's to stop and browse. Once the flowers have been pollinated, the decorative petals will wilt and drop. The plants will then devote much of their energy to producing baby plants that will carry on their genetic line. The developing plants develop inside a protective seed, which is encased in the fruit.
One notable plant that bears fruit in the Summer in the Headlands is the native California blackberry (Rubus ursinus). Blackberries are common in the Marin Headlands and are an important part of the habitat for many animals. Many species of birds enjoy the sweet juicy fruit, deer browse on the foliage, and small animals find shelter in the protective spaces offered by the prickly plant.
California Blackberry
Photo Credit: Charles Webber
California Academy of Sciences
Summer Water
Rodeo Lagoon at Sunset
The dynamic Rodeo Lagoon changes again once summer arrives. The water turns milky green in color when conditions are right for an algal bloom. The presence of nutrients in the water combined with longer growing days stimulate the growth of algae in the lagoon. There is so much algal productivity during this time that they literally cloud the water, blocking sunlight from reaching the lagoon floor. These blooms come to an end once nutrients in the water are used up. The massive explosion of plant life is followed by a period of death and decay as the algae die. As the huge biomass of algae gets decomposed by bacteria, dissolved oxygen in the water gets used up in the process. If dissolved oxygen levels become low enough, the decay of algal bloom can cause a fish kill.
Three-Spine Stickleback
Photo credit: Paul Barrow
Fish, such as the three-spine stickleback and the prickly sculpin, are sensitive to dropping levels of oxygen in the water and some may die following an algal bloom. The die-off of algae and fish is accompanied by an unpleasant smell. However, this cycle of life and death is a natural part of the ecology of Rodeo Lagoon. A healthy lagoon ecosystem is able to recover from moderate levels of disturbance.
Return to mandala of the seasons.
