A study on the impact of a non-native tunicate called Didemnum vexillium—a Western Pacific native that has spread to the U.S., Europe and New Zealand within the past two decades—found that it hampered the growth of eelgrass in a study area on the west shore of Tomales Bay. Ted Grosholz, one of the study’s authors and a professor at the University of California, Davis, who does research at the Bodega Bay Marine Lab, said he…