Monterey Bay Aquarium Research Institute
Marine Botany


taxonomy morphology chemistry life history ecology



Postelsia occupies mid to upper intertidal environments of high wave energy subject to elevated disturbance rates. Potential benefits to this wave-swept environment may include: i) increased nutrient transport to the alga - there is no stagnant water surrounding the palm to be depleted of nutrients, and ii) increased productivity - continual wave movement of the alga will increase the percentage of fronds receiving direct sunlight.

Soberanes Point in Garrapata State Park

Soberanes Point in Garrapata State Park

Constant wave shock also aids the persistance of sea palm populations. Direct wave force and/or contact by logs, rocks, etc. carried in the surf will remove mussels and other competitors from the substratum, providing space for spores to germinate. In absence of such disturbance, Postelsia is unable to spread its population to neighboring space and may possibly be outcompeted by other species. Recruitment in areas of recent mussel removal is especially strong, suggesting that mussels may provide "protection" for Postelsia's gametophyte stage during fall/winter. Once mussels are removed, spores settled on the rock beneath the mussel bed will have an advantage to develop before other organisms can enter the cleared space. Postelsia may also create its own disturbance. Observations have shown that "pioneer" sporophytes settled on other organisms (mussels, barnacles, algae) will, with the aid of wave force, rip these organisms from their substratum, again clearing space for spores settled underneath to develop.
wave washed rock with sea palms intertidal rock with sea palms sea palm high and dry

Wave forces are especially strong during winter storms. Postelsia's heteromorphic life history is particularily suited to such seasonal fluctuation. The clear morphological differences exhibited between Postelsia's gametophyte and sporophyte stages may have evolved in response to this environmental change. As compared to their larger sporophyte counterparts, microscopic gametophytes can essentially "hide" from elevated wave force during winter months.

Organisms frequently associated with Postelsia include mussels (Mytilus californianus), barnacles, and corraline algae. The mussels are the dominant competitor in this habitat; mussel patches can sustain themselves even when surrounded by Postelsia sporophytes. It is thought that the mussels "prevent" sporophyte development in their beds by either ingesting the spores or grinding them between their shells. Postelsia may also be grazed upon my chitons and limpets, although the alga's quick growth rate may help Postelsia to withstand such consumption.

coralline algaetiny sea palms

copyright 1999 sarah oehm
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Last updated: Feb. 05, 2009