December 6th, 2017
California has received a lot of rain so far this winter- we have been waiting through several years of drought for this! The last time we needed our umbrellas this often was the winter of 2010-2011. Many of California’s heavy rains are from a type of storm called an atmospheric river, or a pineapple express. We know how heavy rains can affect us- we have seen frequent flooding of major roadways and cities this winter in the bay area. How do heavy rains affect water in the bay, and the animals that live there? Scientists from the SF Bay NERR, along with colleagues from the Smithsonian Environmental Research Center and UC Davis, recently published some of their research on this question in the scientific journal Proceedings of the Royal Society B.
Our team regularly monitors the native Olympia oyster throughout San Francisco Bay, focusing on the Marin shoreline around our reserve site at China Camp State Park. In some years, China Camp has an enormous oyster population that is significantly larger than anywhere else in the bay where we work. However, when we got to our field sites at China Camp in spring 2011, almost every oyster was dead! What happened? When freshwater flows into the bay from rain storms or snow melt, the salinity of the bay declines. Different species of animals that live in the bay can tolerate different salinity levels and if levels are too low for a species it can cause problems. Lead author Brian Cheng knew from his past research that Olympia oysters are able to survive in low salinity water by sealing their shell valves shut, but can only do so for about 8 days before they start to die. Salinity data from our reserve’s water quality station at China Camp was then analyzed alongside precipitation data associated with atmospheric river storms. There were many atmospheric rivers throughout the 2010-2011 winter, and we found that salinity at China Camp stayed at a low level below approximately 6 psu for 8 days following a cluster of atmospheric river storms in March. This research shows the biological impacts of atmospheric rivers on natural ecosystems: this mass die-off of native oysters coincided with a series of atmospheric rivers and the resulting long period of low salinity at China Camp.
How is all the rain affecting our bay this winter? Here is a graph of salinity data from China Camp since December 2016. The orange line shows salinity at 6 psu, the low level associated with the oyster die-off in 2011. From what you learned above from our previous research, what do you predict oyster densities might look like this coming spring during our surveys?