By Mia Davidson and Jan Sattler
The giant keyhole limpet shell (Megathura crenulata) was used as wampum by Laguna’s original residents. They found the five inch buff to white domed oval shells with an opening at the apex (a keyhole) in the water and washed up on beaches. The limpets, sometimes known as whale’s eyes, are a primitive type of snail or gastropod closely related to the abalone. Ranging from Monterey, Calif., to the middle of Baja California, the giant keyhole limpet is most commonly found in sheltered areas of the intertidal zone up to 100 feet deep, or in the tidepools attached to the rocks.
Giant keyhole limpets belong to a family of long-lived mollusks that have a single shell with a broad muscular “foot” on the underside of their body. They are the world’s largest keyhole limpet with the size of the shell reaching up to five inches in length. Their soft fleshy body lies below the shell and extends beyond the shell. A mantle covers much of the shell and can be solid, mottled or striped and range in color from beige to black, whereas their foot is yellowish-orange.
The limpets breathe by drawing water over their gills and expelling it through the hole in the top of their shell. The keyhole is also used to expel waste. Primarily herbivores, giant keyhole limpets feed at night using a radula (rasping tongue) located on its yellow-orange underside as they slowly move over the rocks scraping off algae, tunicates and sponges before returning to their home scars (resting places).
There has been increasing concern about possible population declines due to overharvesting because of their importance in the biomedical field. Giant keyhole limpets produce a protein that is vital to medical testing and the manufacture of several cancer medications that cannot be synthetically reproduced. Due to the importance of the protein, the government has been sponsoring studies to establish giant keyhole limpet farms to secure a sustainable source for the future. In addition, because of the interdependence of marine life, loss of this species may have unforeseen cascading impacts on other species and a detrimental effect to the near shore environment as a whole.
Residents Mia Davidson and Jan Sattler are year-round ocean swimmers and board members of Laguna Ocean Foundation, which educates the public about the near shore environment and intertidal zone. Info: www.lagunaoceanfoundation.org