Mapping oysters on the Pacific coast of North America: A coast-wide collaboration to inform enhanced conservation

Abstract

To conserve coastal foundation species, it is essential to understand patterns of distribution and abundance and how they change over time. We synthesized oyster distribution data across the west coast of North America to develop conservation strategies for the native Olympia oyster (Ostrea lurida), and to characterize populations of the non-native Pacific oyster (Magallana gigas). We designed a user-friendly portal for data entry into ArcGIS Online and collected oyster records from unpublished data submitted by oyster experts and from the published literature. We used the resulting 2,000+ records to examine spatial and temporal patterns and made an interactive web-based map publicly available. Comparing records from pre-2000 vs. post-2000, we found that O. lurida significantly decreased in abundance and distribution, while M. gigas increased significantly. Currently the distribution and abundance of the two species are fairly similar, despite one species being endemic to this region since the Pleistocene, and the other a new introduction. We mapped the networks of sites occupied by oysters based on estimates of larval dispersal distance, and found that these networks were larger in Canada, Washington, and southern California than in other regions. We recommend restoration to enhance O. lurida, particularly within small networks, and to increase abundance where it declined. We also recommend restoring natural biogenic beds on mudflats and sandflats especially in the southern range, where native oysters are currently found most often on riprap and other anthropogenic structures. This project can serve as a model for collaborative mapping projects that inform conservation strategies for imperiled species or habitats.

Intra-decadal increase in globally-spread Magallana gigas in southern California estuaries

“…In North America, increases in M . gigas recruitment since 1945 are strongly correlated with warming waters [ 23 ] and have been observed in estuaries across British Columbia, the U.S. West Coast, and Baja California, Mexico [ 24 ].…”

“…These range expansions have not been limited to European coasts; M. gigas have been introduced to every continent aside from Antarctica [16]. In North America, increases in M. gigas recruitment since 1945 are strongly correlated with warming waters [23] and have been observed in estuaries across British Columbia, the U.S. West Coast, and Baja California, Mexico [24].…”

Identifying refuges from climate extremes to enhance conservation in a shallow estuary

“…Persistence of fresh water that lasts several days has wiped out large portions of these communities. In 2006, 2011, and 2017, extreme precipitation caused periods of low salinity in parts of SFB leading to near-complete mass mortality of invertebrate and seagrass communities adapted to saline estuarine conditions, and community assembly shifted as a result (Grosholz et al 2008 One impacted invertebrate was the Olympia oyster (Ostrea lurida), a native foundation species that lives in the intertidal and shallow subtidal zone of West Coast embayments from British Columbia, Canada to Baja California, Mexico (Baker 1995;Kornbluth et al 2022). As foundation species, oysters engineer high-value habitat that increases the diversity and abundance of numerous native species (Kimbro and Grosholz 2006; Ramsay 2012; Boyer at al.…”

“…However, across their range, Olympia oysters have lost an enormous proportion of their historic spatial extent, and this downward trajectory is continuing into the 21st century (Zu Ermgassen et al 2012; Kornbluth et al 2022).…”

“…While warm temperatures can be beneficial for Olympia oysters to an extent, it is possible that the marine heat wave influenced biotic and abiotic conditions for oysters in SFB, such as food availability or dissolved oxygen. Further research would be required to confirm if the marine heat wave may have contributed to the 2015 SFB Olympia oyster decline, and how that can be factored into restoration planning.Olympia oyster populations are continuing to decline even in the 21st century, despite efforts to conserve and restore them(Kornbluth et al 2022). Today's smaller existing population size may limit Olympia oysters' reproductive output and genetic diversity, making recoverymore difficult.…”