Marine Science

Marine Science

Senior Theses 2009

Kaela Wuesthoff

Seasonal Distribution of Algal Symbionts of Anthopleura elegantissima in the Intertidal Zone

Thesis Committee: David Hastings (chair), Nancy Smith, Jonathan Cohen

This study examined the temperate sea anemone Anthopleura elegantissima found in the Pacific Northwest rocky intertidal zone.  A. elegantissima host up to two different algal symbionts concurrently: a brown unicellular algae called zooxanthellae (Symbiodinium, dinophyte) and a green unicellular algae called zoochlorellae (Trebouxiophyceae, chlorophyte). The distribution of these highly productive cnidarians and their symbionts were measured for this study, along with environmental parameters that may affect their location in the intertidal zone.  Zooxanthellae can inhabit areas of warmer temperatures and higher light exposure than zoochlorellae, creating a hypothesized progression of zoochlorellate anemones to zooxanthellate anemones with increased tidal height.  The study analyzed anemones on a single rocky outcrop at Cattle Point, San Juan Island, Washington in 2008.  This field site was used in previous study of A. elegantissima in which a majority of zoochlorellate (>85% zoochlorellae algae) anemones were found.  Zooxanthellate (>85% zooxanthellae algae) dominated throughout the intertidal zone over the two seasons (July n= 56, November n= 54), while most zoochlorellate occurred at the lower tide height.  During periods of aerial exposure temperature exceeded 30C in the summer and 18C in early fall, possibly excluding zoochlorellate anemones from populating the higher intertidal.  Algal density remained constant over tide height and season in zooxanthellate anemones; zoochlorellate algal densities being higher may be due to higher growth rate (mitotic index).  Chlorophyll concentrations in July are higher than November concentrations possibly due to the decrease in light intensity during the seasonal change.  Spikes in chlorophyll a at the mid tide height in July and chlorophyll c at the low tide height in November could be due to prevalence of low-light environments or microhabitats at these tide heights.  Distribution of different microhabitats was evident within the intertidal zone for both seasons and might relate to symbiont type.  Overall, the expected distribution of algal symbionts was not strongly evident, with zooxanthellae not being restricted to a particular tide height in the intertidal.  The environment and physical location appear to influence the distribution of zooxanthellae and zoochlorellae through the environmental parameters of light intensity and temperature.  It is evident that both zoochlorellate and zooxanthellate A. elegantissima have adapted to these environmental influences due to the stability of their populations over time.

Student Research