Professor California State University, Fullerton, United States
Abstract: Over the past decades, estuarine ecosystems have suffered significant habitat loss. Implementation of multi-habitat living shorelines (MHLS) 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 at four sites. Increased sedimentation from eelgrass could threaten oysters and other filter feeders. This study investigated 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 calculated the total biomass and per capita condition indices of native and non-native filter feeders on restored oyster beds one- and four-years post-restoration. I hypothesized that increased eelgrass density would 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 (n=10 quadrats per bed), identified by species, and weighed to determine wet and dry tissue and shell weight, and quantified condition index. I quantified sedimentation by measuring mud deposition directly on oyster beds using a periodontal probe and quantified filter feeder and eelgrass densities using quadrat surveys.
Mud deposition was generally not impacted by eelgrass, except at one site, Pacific Coast Highway, where deposition was higher where oyster beds were restored alone. For biomass we saw four species impacted; Ostrea lurida, Crucibulum spinosum, and Mytilus galloprovincialis had 2X, 4X, and 2X higher biomass, respectively, on oyster beds restored alone vs. with eelgrass, but only at one site, Deanza, while Musculista senhousia had a higher biomass on oyster beds restored alone vs. with eelgrass across all sites. For condition index we saw three species impacted; C. spinosum had a 20% higher condition index on oyster beds restored alone vs. with eelgrass, M. senhousia had 20% higher condition index on oyster bed with eelgrass vs. alone at Deanza, and O. lurida had 25% higher condition index on oyster beds restored alone vs. with eelgrass at Deanza. Overall, eelgrass did not increase sedimentation onto restored oyster beds. When considering filtration function, co-restoration is not recommended, but other research in our laboratory suggests that co-restoration increases biodiversity, eelgrass growth and sedimentation, and decreases upshore wave energy. 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.
