Magallana gigas Density and Height, Newport Bay and San Diego Bay, CA, USA, 2010-2020

We tracked changes in density and size distribution of the non-indigenous oyster, Magallana gigas in two southern California, USA bays over the decade spanning 2010 – 2020 using randomly placed quadrats across multiple intertidal habitats (e.g., cobble, seawalls, riprap) and documented density increases by 2.2 to 32.8 times at 7 of the 8 sites surveyed across the two bays. These increases in density were coincident with 2 – 4° C increases in median monthly seawater temperature during summer months, consistent with global spread of M. gigas elsewhere. Size frequency distribution data, with all size classes represented across sites, suggest now-regular recruitment of M. gigas. Our data provide a baseline against which to compare future changes in density and abundance of a globally-spread NIS of significant concern.