Weekend plans to visit British Columbia’s Juan de Fuca Provincial Park went astray, so I am instead sharing images from last year’s low tides trip. This is the Botanical Beach site where I’ve previously photographed sea palm and stiff-stiped kelp. In the first photograph, Postelsia palmaeformis occupies the rocks with the mussels, while Laminaria setchellii is partially submerged by the water in the lower right portion of the image.
Postelsia palmaeformis is native to the rocky coasts of western North America from California to British Columbia. Formerly thought to be in the Lessoniaceae, it was moved along with several other well-known alga species into the Laminariaceae, based on molecular evidence (see: Lane et al. 2006. A multi-gene molecular investigation of the kelp (Laminariales, Phaeophyceae) supports substantial taxonomic re-organization. Journal of Phycology. 42:493–512). However, you will still see many references citing the previous family, including the Encyclopedia of Life: Postelsia palmaeformis. The EOL entry has a summary article with many factoids about sea palm, including:
- it’s the only species of kelp that can stand unsupported in air
- despite living in a marine environment, this annual species is thought to only disperse 1-3m (~3-10 ft.) per reproductive cycle
- it only inhabits sites with strong waves; it will not survive in calm water
And, also from EOL (author Elaine Soulanille), a complex relationship with mussels:
Postelsia has a complex relationship with the mussel, Mytilus californianus, that covers much of its rocky habitat. Bare rock is the best place for sea palms to settle, but if there isn’t any nearby, it will settle on the mussels. The mussels will still eventually crowd it out, unless something removes a clump, leaving room for Postelsia. It’s usually strong waves that suck the mussels from the rocks. And mussels with Postelsia growing on their shells are more likely to be removed. So sea palms can “help” make space for themselves in the mussel-bed. But the mussels may actually help Postelsia survive during parts of its life-cycle, the tiny gametophyte (egg or sperm-making) stage and the young sporophyte (palm-tree-shaped) stage, by providing protection from harsh sun and drying air.