Anthopleura elegantissima is the most abundant sea anemone in intertidal communities of the northeast Pacific Ocean. This dominant invertebrate plays an important role in the ecology of these systems. Because of the unique symbiotic relationship A. elegantissima has with two distinct photosynthetic algae, it is also important as a model to help us better understand symbiotic partnerships and how they respond to a changing environment. The relative abundance of the two algae in A. elegantissima populations along the outer coast of Washington State will be assessed. This will provide a barometer for climate change; the distributions and abundances of the two symbiont species are predicted to shift if, for example, temperature or light levels change. This prediction is based on the different physiological tolerances of the algal symbionts (one prefers cooler, low-light environments while the other does better in warmer, high-light environments). In laboratory studies, the relative value of each symbiont will be tested by measuring their impact on growth and reproduction of the anemone host. Anemones will be exposed to different levels of natural sunlight, and sexual reproduction, asexual division, and body growth will be monitored. Health of the symbionts will also be measured in terms of photosynthetic productivity and division rate. Results of the work will provide valuable insights into the ecology of an important and abundant intertidal species. Results will also be important for developing testable hypotheses about how other long-lived species with multiple symbiotic partners (e.g., lichens and corals) will be affected by climate change-related shifts in symbiont complements. This project will engage in symbiosis research 14 undergraduate and 2 graduate students, including members of groups underrepresented in science. Elements of the project will be incorporated into existing undergraduate courses and an elementary school outreach program, and also disseminated through public lectures.
Symbiotic relationships, where two genetically distinct organisms live in close association with one another, are fundamental to the biology and ecology of numerous marine and terrestrial species. In associations of this kind, the abundance, identity and physiology of the symbiont can critically affect success of the host. Our goal was to determine how the presence and identity of photosynthetic endosymbionts (symbiotic partners living within the bodies of their hosts) affect the sea anemone Anthopleura elegantissima. Because A. elegantissima host two very different symbionts (green algae called zoochlorellae and dinoflagellates called zooxanthellae), and because the anemones can also exist without symbionts, this species provides a particularly good system for measuring the effect of symbiont complement on host performance. Through a combination of field surveys and laboratory and field experiments, we determined that hosting different symbionts affects growth, reproduction and life history strategy of A. elegantissima. In particular, individuals hosting zoochlorellae tend to reproduce sexually while those hosting zooxanthellae adopt a more clonal (asexual) strategy. This difference in life history could have important consequences for ecology of this species and for dynamics of the communities in which it occurs (A. elegantissima is the most common intertidal sea anemone along the west coast of North America). We found that light intensity and temperature affect the two A. elegantissima endosymbionts differently. Zoochlorellae experience significant stress under high light condition, fixing less carbon and growing more slowly. The effect is much less obvious in zooxanthellae. The A. elegantissima respond behaviorally to the stressed symbionts, showing clear patterns of exposing and shading the oral disk and tentacles under high light or temperature conditions. This may be a strategy to minimize the damage caused by reactive oxygen species produced through the photosynthetic pathways of the stressed symbionts. Data collected from field sites suggest that the symbiont complements of A. elegantissima may be changing, moving away from zoochlorellae toward zooxanthellae. Likely due to increasing mean seawater temperature in the study area, this shift may allow the A. elegantissima to persist and thrive even as environmental conditions change, but may also carry consequences related to changes in basic life history characteristics of the anemones (e.g., shifting from sexual to asexual reproductive strategies). A primary objective of our work has been to involve undergraduate and graduate students in meaningful research, training them and providing opportunities to directly engage in science. Over the course of this project, we have supervised the research of 13 undergraduate and 5 graduate researchers. Four of the undergraduates were participating in the NSF-sponsored Research Experience for Undergraduates program at the Shannon Point Marine Center. The fifth was a community college student in the NSF Centers for Ocean Sciences Education Excellence program. Eight additional students, all individuals from groups underrepresented in the sciences, were participating in the Multicultural Initiative in the Marine Sciences: Undergraduate Participation (MIMSUP) program. The student were full research partners in all aspects of the project including research presentations at conferences, informal presentations to the public, and publication of results in the refereed science literature. Results were also disseminated to the public through outreach to K-12 classrooms in the local school district, though community science events and through public lectures.
