August 1, 2019.
Invasive species can lead to serious ecological changes. The San Francisco Bay area is one of the most invaded areas in the world due to the commercial shipping industry and recreational water vessels. While the intertidal is not widely invaded, the harbors and docks are. One exception to this is the invasive, colonial filter-feeding bryozoan Watersipora, which has been found at various rocky outer coast sites. Further investigation into how the sites are invaded by this organism and their impact on native species must be carried out. In this project, at four intertidal sites around the SF Bay outflow, we compared Watersipora abundance at two tidal heights and assessed interactions with organisms. Using two parallel transects, separated by approximately 8 meters, we documented size and growth form of all colonies located one meter to each side of the transect. To assess community interactions, we centered a 15x15 centimeter quadrat over every other colony and photographed it. Using the photographs, organisms within each quadrat were quantified and interactions between Watersipora and organisms were assessed. At all sites, Watersipora abundance was higher in the lower intertidal than the shoreward transect. Comparing the four sites, the two sites more distant from the outflow had more total counts of colonies, in comparison to the two bay proximal sites. This may suggest that the bay outflow isn’t the source of Watersipora spread along the coast, even though it is abundant inside the Bay itself. Investigating community composition around Watersipora colonies showed most interactions with coralline algae, sponges, polychaete tubes, and anemones. Specifically, it was observed overgrowing Phragmatopoma californica tubes, and both overgrowing and being overgrown by sponges. Looking forward, investigation into how Watersipora impacts species in the same ecological niche will be critical to understanding how this invasive organism is impacting the rocky intertidal community.
Biology | Ecology and Evolutionary Biology
C. Sarah Cohen
Romberg Tiburon Center for Environmental Studies (RTC)
The 2019 STEM Teacher and Researcher Program and this project have been made possible through support from Chevron (www.chevron.com), the National Science Foundation through the Robert Noyce Program under Grant #1836335 and 1340110, the California State University Office of the Chancellor, and California Polytechnic State University in partnership with the SFSU Estuary and Ocean Science Center at the Romberg Tiburon Campus. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the funders.