Friend or foe? Effect of Eelgrass Density on Filter Feeder Biomass and Condition Index in a Multi-habitat Living Shoreline

Background/Question/Methods

Over the past decades, estuarine ecosystems have suffered significant habitat loss. Implementation of multi-habitat living shorelines can restore lost habitat function. Researchers constructed a MHLS from 2016 to 2017 in Newport Bay, California by restoring eelgrass and oyster beds together and in isolation. Increased sedimentation from eelgrass could threaten oysters and other filter feeders. This study will investigate how eelgrass impacts filter feeder biomass and condition index. To compare short-term and longer-term success of oysters restored with varying densities of adjacent eelgrass, I will calculate the total biomass and per capita condition indices of native and non-native filter feeders on restored oyster beds one- and two-years post-restoration. I hypothesize that increased eelgrass density will increase sedimentation rates onto adjacent oyster beds, causing declines in filter feeder biomass and per capita condition indices. I excavated filter feeders from quadrats on oyster beds, identify by species, and weigh to determine wet and dry tissue and shell weight, and quantify condition index. I quantified sedimentation by measuring mud deposition on oyster beds using a periodontal probe and quantified filter feeder and eelgrass densities using quadrat surveys.

Results/Conclusions

Mud deposition during each year from 2018 to 2020 was significantly higher on oyster beds restored adjacent to eelgrass vs oyster beds restored alone. In 2018, every species had higher biomass on oyster bed restored alone vs. with eelgrass. In 2018, M. senhousia had higher condition index on oyster bed restored with eelgrass vs. alone. Increasing understanding of the relationship filter feeders share with eelgrass will inform future management decisions about whether to restore multi-habitat living shorelines together or in isolation.