Reef design and site hydrodynamics mediate oyster restoration and marsh stabilization outcomes

Abstract

The detrimental ecological impacts of engineered shoreline protection methods (e.g., seawalls) and the need to protect the coastal zone have prompted calls for greater use of natural and nature‐based infrastructure (NNBI). To balance competing needs of structural stability and ecological functioning, managers require assessments of NNBI designs and materials for differing environmental settings (e.g., among wave‐energy regimes). To examine the effects of setting and oyster‐based NNBI design on the provision of shoreline protection, we constructed reefs from two substrates: a novel, biodegradable material (Oyster Catcher, OC) and traditional oyster shell bags (SB) on low‐ and high‐energy eroding salt marsh shorelines, designated based on fetch and boat wake exposure. Both reef types buffered marsh elevation change on the high‐energy shoreline relative to unaltered controls, but only SB reefs were able to do so on the low‐energy shoreline. Additionally, both shorelines experienced high ambient rates of retreat and declines in marsh vegetation shoot density. Although constructed reefs did not mitigate marsh retreat on the low‐energy shoreline, novel OC reefs significantly reduced retreat relative to SB reefs and control sites (no reefs) on the high‐energy shoreline. Those SB reefs were severely damaged by storm events, increasing their areal footprints at the expense of vertical relief. Conversely, OC reefs on both shorelines exhibited steady oyster recruitment and growth and hosted higher densities of larger oysters. To successfully provide shoreline stabilization benefits, oyster‐based NNBI must be structurally stable and able to promote sustained oyster recruitment and growth. Our results indicate that deliberate decisions regarding NNBI substrate, siting, and configuration can produce resilient reefs, which reduce rates of erosion and, in some cases, enhance vertical accretion along salt marsh edges. The growth trajectory, structural stability, and co‐benefit provisioning of OC reefs demonstrate the potential of alternative restoration substrates to provide valuable oyster habitat along threatened marsh shorelines.

Assessing habitat enhancement by living shoreline restoration: exploring potential caveats of nekton community metrics

“…The breakwaters also provide structurally complex habitats, and hard substrate favorable to the settlement of ecosystem engineers such as oysters (Morris et al 2019). Successful LS breakwaters also stabilize sediments (Morris et al 2019; Luom et al 2021; Wellman et al 2022), and provide favorable ground for the establishment of a more diverse assemblage of prey types (Bilkovic et al 2016; Bilkovic & Mitchell 2017; Wellman et al 2022). In addition, the stabilization and recovery of marsh shorelines from steep eroding edges (such as the ones at our control sites) to more gently‐sloped aggrading shorelines will allow more opportunities for nekton to access the flooded marsh surface and the benefits they gain from doing so (Minello et al 2012; Baker et al 2013; Plumlee et al 2020).…”

The Use of Non-Plastic Materials for Oyster Reef and Shoreline Restoration: Understanding What Is Needed and Where the Field Is Headed

“…Two additional types of restoration units were included in Table 1 as they were mentioned by multiple respondents; soft-sided gabions are similar to rigid gabions with the exception of using lighter-weight metal mesh to make the resulting structure more flexible in shape, and Oyster CORE (Community Oyster Reef Enhancement) modules that incorporate natural fibers, wood chips, cement, and oyster shells into low-profile blocks. Additional non-plastic material designs published in the peerreviewed literature include cement Oyster Castles ® (e.g., [30]), Portland cement-infused jute structures called Oyster Catchers™ (e.g., [64]), and Pervious Oyster Shell Habitat (POSH) that combines cement and oyster shell [65]. Non-plastic materials are being tested at every project scale in Florida, and scale was shown to be an important factor in determining the approach for reducing or eliminating plastic in oyster and living shoreline restoration.…”