FRIEND OR FOE? EFFECT OF EELGRASS ON FILTER FEEDER BIOMASS AND CONDITION INDEX IN A MULTI-HABITAT LIVING SHORELINE

Over the past decades, estuarine ecosystems have suffered significant habitat loss. Multi-habitat living shorelines (MHLS) implementation can restore lost habitat function. Researchers constructed a MHLS in 2016-2017 in Newport Bay, CA by restoring eelgrass and oyster beds together and in isolation at each of four sites. I hypothesized that eelgrass would increase sedimentation rates onto adjacent oyster beds, causing declines in oyster and other filter feeder biomass and per capita condition indices (CI). One year (2018) and four years (2021) post-restoration, I excavated filter feeders from replicate quadrats on oyster beds, identified them by species, weighed them to determine wet and dry tissue and shell weight, and quantified CI. I quantified sedimentation by measuring mud deposition on oyster beds using a periodontal probe and quantified eelgrass densities using quadrat surveys. Mud deposition was not affected by eelgrass presence or density, except in 2018 at one of three sites, where deposition was higher when oyster beds were restored without eelgrass. After one year, eelgrass presence decreased native oyster and non-native mussel biomass and increased native and non-native mussel condition indices. Eelgrass density had no effect on filter feeder biomass or CI at one and four years post-restoration. 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.