The Sea Palm seaweed, Postelsia palmaeformis, must be one of the hardiest around. It only lives in areas subjected to heavy surf in the mid- to lower intertidal zone. It needs to be the very robust species that it undoubtedly is because it has to take a lot of pounding from the sea. It stands like a miniature palm tree, attached to rocks clad with large California Mussels and the prehistoric-looking short-stalked Goose Barnacles, where it gets flattened to the surface of the rock by every incoming crashing wave and bounces back upright again as if made of rubber immediately the wave starts to ebb.
The Sea Palm is an annual-growing brown alga with a resilient bendable stalk between 20 to 40 cm long. Many blades or fronds extend from the stalk, sometimes as many as a hundred, and these hang down limply when the Sea Palm is out of water. This variety of seaweed is found along the Pacific Northwest Coast of America from Vancouver Island in British Columbia in the north to San Luis Obispo County in California. The photographs shown here were taken on shores around Yachats in Oregon – midway along their north-south range.
The plants appear on the shore seasonally, being absent over winter from late autumn to early spring. They germinate from spores that are formed in the narrow grooves along the blades of the mature specimens – the spores passing down the grooves and dripping off to the rocks beneath them. Some of these will turn into tiny plants of a sexual generation and then fertilised eggs develop into the familiar Sea Palm form. When young, Sea Palms are greenish in colour but as they mature the colour becomes more olive brown.
Two books I have found useful while finding out about the ecology of the Oregon seashores are:
Seashore Life of the Northern Pacific Coast – An illustrated guide to Northern California, Oregon, Washington, and British Columbia, Eugene N. Kozloff, first published 1973 but reprinted with corrections 1993, University of Washington Press, Seattle and London, ISBN 0-295-96084-1.
The Beachcomber’s Guide to Seashore Life in the Pacific Northwest, J. Duane Sept, 1999 revised 2009, Harbour Publishing, Canada, ISBN 978-1-550-17453-3
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