Penny Pinching with Purple Olives
Laguna Beach is known for its rocky coves. But those who enjoy our coast from a distance may not realize that the sandy beaches between the rocky points extend out into the ocean and provide a very different environment than that found on the rocks. The animals that inhabit this ecosystem have adapted to living in the constantly shifting sandy seafloor and one animal that makes its home there is the Purple Olive (Olivella biplicata). The Purple Olive is a gastropod or snail. Growing up to one inch in length, the elongated, spiraling shell is glossy and smooth, variably colored in striated shades of white, bluish-gray to black, tan, lavender and violet. On the base of the shell is an elongated opening colored vivid violet at the tip from which a white or cream colored, fleshy, wedge-shaped “foot” emerges. The inside of the shell is white.
Living in the Eastern Pacific Ocean with a geographic range from Sitka, Alaska to Baja California Sur, the Purple Olive lives in the sandy bottom either singly or in dense aggregations near shore in protected coastlines or out to 150 feet deep in more exposed locations. They are most active at night, often traveling with the tides. During the day, they burrow into the seafloor just under the surface of the sand, leaving a furrow in their wake. While buried, a long siphon is extended that sucks seawater into the mantle cavity and allows them to breathe. Considered to be both a scavenger and an omnivore, they eat kelp blades, sand worms and small invertebrates, as well as dead animals and detritus found in the soft bottom. The Olive Shell is thought to live for eight to 12 years.
Reaching sexual maturity at just over half an inch, the sexes of the Purple Olives are separate with the male tending to be larger than the female. Mating occurs throughout the year when the male attaches himself on top of the female and fertilizes her internally. Over several weeks, several thousand egg capsules are deposited on the hard surfaces of shells and stones scattered on the sand and ultimately emerge as tiny juveniles. Predators include other gastropods such as Moon Snails and California Cones, some species of Seastars, octopus, crabs and gulls. To escape from predators, the Purple Olive will burrow into the sand, crawl away or if necessary, somersault up from the sand, turn upside down and use both sides of its body as wings to swim a short distance away.
For more than 9000 years, the empty shells of Purple Olives were used to decorate clothing and jewelry of coastal Native Americans. In addition, starting 1,000 years ago, beads were produced from the shell and were used for trade and currency. The beads, called Anchum by the Chumash peoples, became the basis of their monetary system. Strung on cord, their value depended on the length, as measured wrapped around a hand. The Purple Olive is not currently on any list as threatened, however like all other organisms, it is vulnerable to global warming, pollution and environmental degradation. In Laguna, one can often see hermit crabs in the tidepools using the empty shell as their home. When swimming in the ocean, Purple Olives can often be found by looking for a trail or a colony of dimples in the sand.
Residents and ocean swimmers Mia Davidson and artist Jan Sattler believe that a better understanding of our local marine resources will advance the protection of this important ecosystem.