I examined the biomechanical factors that influence the sizes of
intertidal macroalgae by studying a population of Fucus gardneri at Fogarty
Creek Point, OR. I constructed a mathematical model to predict optimal
sizes and probabilities of survival for Fucus under conditions of high and
low wave exposure. Predicted optimal sizes of Fucus closely matched the
mean observed sizes of plants collected from wave-exposed and protected
locations. To test this hypothesis in the field, I reciprocally transplanted
Fucus between wave-exposed and wave-protected sites and found that the
degree of wave exposure did not affect survival, but did influence size.
Large Fucus were tattered by waves at exposed sites, and small Fucus grew
at protected sites. These results support the hypothesis that wave forces
can set mechanical limits to size in Fucus.
I experimentally examined the relative influences of wave-induced
disturbance, competition and predation on the sea palm, Postelsia
palmaeformis and its understory community at a wave-exposed site at
Depoe Bay, OR. Postelsia recruitment was affected by seasonal variations in disturbance and was greatest in areas disturbed in winter. Postelsia were most abundant at mid-zone, wave-exposed sites, and their restriction to wave-exposed sites seems to be due both to; 1) the occurrence of predictable winter disturbances at these sites which remove mussels, thereby stimulating sea palm growth from the underlying rock, and 2) high water motion which enhances sea palm growth by increasing nutrient exchange and photosynthesis and preventing desiccation at low tide.
Competition, disturbance and grazing were all important factors in structuring the Postelsia understory community. Postelsia were dominant competitors and their holdfasts overgrew low-lying plants which were torn loose with Postelsia when this kelp was dislodged by winter storm surf. In the absence of this predictable, seasonal disturbance, competitive understory species, such as Corallina dominated primary space.
Intermediate levels of disturbance allowed for the highest understory
species diversity. Limpets played a keystone role by grazing Postelsia, the
competitive dominant during most of the year, and maintained high
levels of species diversity in the algal understory. / Graduation date: 1995
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/34956 |
| Date | 29 August 1994 |
| Creators | Blanchette, Carol A. |
| Contributors | Menge, Bruce, Lubchenco, Jane |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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