Publication Date

Fall 2009

Degree Type


Degree Name

Master of Science (MS)


Moss Landing Marine Laboratories


Michael H. Graham

Subject Areas

Biology, Ecology.; Biology, Oceanography.


Ephemeral algae are early colonizers of the rocky intertidal zone after a disturbance, although the mechanism of early colonization (including benthic microscopic stages and waterborne propagules) is poorly known. Recruitment of the ephemeral Ulva spp. was studied in two types of disturbance manipulations (partial removal of all macroscopic organisms were removed vs. complete removal of all macro- and microscopic organisms) and an un-manipulated control at two tidal heights (high Porphyra zone and low Mazzaella zone). Replicate disturbances were created in August 2007, November 2007, January 2008, and May 2008 and were monitored until August 2008 on a rocky bench north of Pigeon Point, California. Ulva colonization by waterborne propagules (complete removals) was observed throughout the year, whereas Porphyra was restricted to spring recruitment, as expected due to temporal cues (changes in photoperiod) regulating propagule availability. Peak Ulva responses varied in treatments as a function of timing of clearing, whereas peak Porphyra responses varied in locations as a function of timing of clearing. Location and interactions with location (heterogeneity among zones) explained most of the variability in early colonization. Fall and winter clearings experienced opposing responses by Ulva and Porphyra in each zone. Further experimentation is needed to rule out a negative interaction between Ulva and Porphyra in fall and winter disturbances.