LB 11-146 - Multi-factor impacts on condition index of Ostrea lurida, Mytilus galloprovincialis, and Magallana gigas

Background/Question/Methods:

Over the past decades, estuarine ecosystems suffered significant habitat loss. Implementation of multi-habitat living shorelines (MHLS) can restore lost habitat function, including shoreline stabilization and filtration function. Researchers constructed a MHLS in 2016 in Newport Bay, California by restoring eelgrass and oyster beds together and in isolation. Five years later, we compared the health of bivalves recruiting to restored oyster beds vs bivalves recruiting to human-introduced substrates while also exploring effects of tidal elevation on bivalve health. Urbanized estuaries such as Newport Bay with various natural and anthropogenic habitats set the foundation to study how per capita condition index (CI, a proxy for species health) changes among the native Olympia oyster, Ostrea lurida, and two non-native bivalves, Mediterranean mussel, Mytilus galloprovincialis, and Pacific oyster, Magallana gigas. I hypothesize the CIs would change across sites, substrates, and tidal elevations. In November 2021, O. lurida and M. galloprovincialis were collected from seawalls, restored oyster beds, and cobbles at two sites (protected vs. human-impacted) and their CIs were quantified. Subsequently, O. lurida and M. gigas were collected in February 2022 on seawalls and cobbles at one site to determine if tidal elevation also affected the CIs.

Results/Conclusions:

O. lurida and M. galloprovincialis experienced strong inverse relationships between length and CI; as length increased, CI decreased (linear regression, p < 0.05, both species). After removing length effects, O. lurida had a higher CI at a protected site relative to a human-impacted site (2-way ANOVA, site, p = 0.0439). M. galloprovincialis had a higher CI on cobble and restored oyster beds versus seawall, but only at the human-impacted site, and the CI was higher on cobble at the human-impacted versus protected site (2-way ANOVA, site*substrate, p = 0.0001). In February 2022, the bivalve length effect was not detected (linear regression, p >0.05, both species), and neither tidal elevation nor substrate affected the CI of O. lurida and M. gigas (2-way ANOVAs, all factors, p >0.05). Understanding the relationship filter feeders share with site, substrate, and tidal elevation will inform future management decisions about how comparable MHLS are to anthropogenic habitats and can help restoration practitioners construct management strategies to increase individual bivalve health. This information may be transferable across other urbanized estuaries along the U.S. West Coast which is a region of active Olympia oyster restoration.