August 1, 2012.
Testing the salinity tolerance levels of similar invasive species found in the San Francisco Bay
Julia Smith1,2, Elizabeth Sheets2, and C. Sarah Cohen2
1Department of Teacher Education, California State University, Sacramento 2Department of Biology and Romberg Tiburon Center, San Francisco State University
Three non-indigenous colonial ascidian species, Botrylloides violaceus, Botrylloides diegensis, and Botryllus schlosseri, have become well established in San Francisco Bay. Two species, B. violaceous and B. schlosseri, are globally distributed, and understanding the salinity ranges and tolerances of these successful invaders in their introduced habitats is important for predicting their spread. We tested the tolerance of these three morphologically similar species to salinity ranges that they may encounter locally in San Francisco Bay, and globally, in their broad distributions, including a freshwater transit experiment designed to simulate conditions for ships transiting through the Panama Canal. Botrylloides violaceus, B. diegensis, and Botryllus schlosseri were exposed to various salinities (10, 15, 18, and 20 ppt) for a period of 14 hours, and then assessed for two signs of vitality immediately after each treatment, and were monitored for survival after a week. Our preliminary results showed survival of Botrylloides diegensis, and B. violaceus at the lowest (10 ppt) salinity treatment after 1 week, but no colonies of Botryllus schlosseri survived this salinity treatment in a preliminary trial. The three species all showed survival at our higher (15, 18, and 20 ppt) salinity treatments. In a separate trial, the three target species were also exposed to a drastic salinity decrease to 0 ppt for 7 hours, related to conditions in the Panama Canal. There were no signs of immediate survival in colonies that experienced very low salinity conditions. However, small vascular fragments appear to remain in many colonies three weeks later, and are currently being monitored in the event that they may regenerate, as local colonies of each of these speceis have successfully carried out whole body regeneration from vascular fragments as small as 3.9 mm (Benson Chow, unpub. data).
Marine Biology | Other Ecology and Evolutionary Biology | Science and Mathematics Education
Dr. C. Sarah Cohen
Romberg Tiburon Center for Environmental Studies (RTC)
This material is based upon work supported by the S.D. Bechtel, Jr. Foundation and by the National Science Foundation under Grant No. 0952013. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the S.D. Bechtel, Jr. Foundation or the National Science Foundation. This project has also been made possible with support of the National Marine Sanctuary Foundation. The STAR program is administered by the Cal Poly Center for Excellence in Science and Mathematics Education (CESaME) on behalf of the California State University (CSU).