Dataset: Oyster drill functional eradication field study - quadrat surveys in San Francisco Bay from 2017-2018

Site selection

To quantify the relationship between oyster drills and native oysters, we established eight intertidal field sites in Richardson Bay, CA. Of these sites, we further focused on a subset of four sites, establishing two sites for community science-based oyster drill removals and two sites as paired controls. One of our removal sites, Lani’s Beach (hereafter Lani’s) was selected because of easy access, high public use, and because it is valuable to the community due to its use in outdoor educational programs at the immediately adjacent Richardson Bay Audubon Center & Sanctuary. Lani’s was paired with a control area that was separated by 50 m along shore (Cheng et al. 2021; Fig. 1, Supplementary Information S1). Second, we used two sites located on Aramburu Island because of extensive habitat restoration activities that were completed by the Audubon Society in 2010. The Aramburu removal and control sites were separated by 140 m along shore. The quadrat survey reported here is for the four core sites.

 

Benthic sampling

To quantify the abundance of Urosalpinx and its relationship to native oysters, we conducted quadrat surveys at each of the four field sites. At each site, we established a permanent 30 m transect at 0.5 m above mean lower low water (MLLW). Along each transect, we censused all oyster drills and oysters at the surface and by overturning all stones within 10 randomly distributed 0.5 x 0.5 m quadrats. Quadrats were randomly stratified such that five were conducted between 0 and 15 m of the transect and the remaining five occurred between 15 and 30 m. For each site, surveys occurred two to five times (20–50 quadrats, mean = 40.5 quadrats) during the low tides of summer, fall, and winter of 2017 and spring and summer of 2018. 

 

Functional eradication of drills

At each removal site, we established a 60 m swath of shoreline (along shore) from the lower mud zone to the upper barnacle zone (approximately 15 m across shore) to serve as the focal area for removals. For the removal sites, the 60 m total swath included the 30 m fixed transect with additional 15 m buffer zones on each side (along shore). Paired with each eradication site, we established a similar swath of shoreline to serve as a control area except snails were not removed from these areas. Control and removal zones were also separated by stretches of shoreline that did not have hard substrate, potentially limiting the movement of oyster drills. All areas were marked with stakes for the duration of the experiment. We organized drill removal events, inviting members of the public to assist us in finding and removing drills. To increase community participation, we scheduled drill removals on weekends and only during daylight low tides. In 2017, we organized four removal days at Lani’s and three at Aramburu; in 2018, we held three removal days at each location. Between 20 and 35 people participated at each event and were provided project background and training prior to removal efforts. Teams then worked for 1–2 h, removing snails by hand from the focal areas described above. Teams also searched for snails on the surface of the mud, but these were rarely found. To ensure complete spatial coverage of the removal area, we divided removal and buffer areas into * 2 m wide swaths running perpendicular to shore and assigned volunteers to these zones. Collected snails were taken to the Smithsonian Environmental Research Center’s Tiburon, CA laboratory (housed at the Estuary and Ocean Science Center, San Francisco State University) and frozen.