Masters Thesis

A long term comparison of rocky intertidal communities in Redwood National and state parks

Long term comparisons are important for understanding intertidal community dynamics and documenting response to environmental pressures. This study compares the historical abundance of high intertidal sessile organisms at two rocky intertidal sites within Redwood National and State Parks shortly after the park was established (“historical”:1974-1976) to the present community (2004-2005) at the same locations. Percent cover of ephemeral, early successional species was higher in historical assessments, whereas percent cover and magnitude of seasonal variation in perennial, late successional organisms increased in assessments of the present community. The long term successional shift is likely a result of decreased disturbance severity between the mid 1970’s to present. Severe historical disturbance is linked to increased sedimentation and frequent driftwood battering associated with logging. Conservation and rehabilitation strategies in the adjacent terrestrial landscape since 1978 may have resulted in spatial dominance by mid to late successional species at these two sites. Several alternative causal hypotheses regarding long term climate change, El Niño Southern Oscillation, upwelling intensity, and species interactions are evaluated, but not supported by the results of this study.