Large‐scale variation in wave attenuation of oyster reef living shorelines and the influence of inundation duration

Abstract

One of the paramount goals of oyster reef living shorelines is to achieve sustained and adaptive coastal protection, which requires meeting ecological (i.e., develop a selfsustaining oyster population) and engineering (i.e., provide coastal defense) targets. In a largescale comparison along the Atlantic and Gulf coasts of the United States, the efficacy of various designs of oyster reef living shorelines at providing wave attenuation was evaluated accounting for the ecological limitations of oysters with regard to inundation duration. A critical threshold for intertidal oyster reef establishment is 50% inundation duration. Living shorelines that spent less than one-half of the time (<50%) inundated were not considered suitable habitat for oysters, however, were effective at wave attenuation (68% reduction in wave height). Reefs that experienced >50% inundation were considered suitable habitat for oysters, but wave attenuation was similar to controls (no reef;~5% reduction in wave height). Many of the oyster reef living shoreline approaches therefore failed to optimize the ecological and engineering goals. In both inundation regimes, wave transmission decreased with an increasing freeboard (difference between reef crest elevation and water level), supporting its importance in the wave attenuation capacity of oyster reef living shorelines. However, given that the reef crest elevation (and thus freeboard) should be determined by the inundation duration requirements of oysters, research needs to be refocused on understanding the implications of other reef parameters (e.g., width) for optimizing wave attenuation. A broader understanding of the reef characteristics and seascape contexts that result in effective coastal defense by oyster reefs is needed to inform appropriate design and implementation of oyster-based living shorelines globally.

Oyster Reef Surfaces in the Central Wadden Sea: Intra-Reef Classification and Comprehensive Statistical Description

“…Further, the reported parameters were chosen as they have been identified to exert an influence on the surrounding hydrodynamics in environmental hydraulics (Nikora et al, 1998;Aberle and Nikora, 2006;Coleman et al, 2011;Flack and Schultz, 2014;Navaratnam et al, 2018) and mechanical engineering (Flack and Schultz, 2010;Chung et al, 2021). Hence, a comprehensive set of topographical parameters has been provided adding to the call for understanding of roughness effects of this relatively new biogenic habitat on the intertidal flats of the central Wadden Sea (Markert et al, 2010;Borsje et al, 2011;Walles et al, 2015b;Folmer et al, 2017) and worldwide (Morris et al, 2021).…”

“…Previous studies have used a mean number of roughness elements, their average height and width as site-specific topographic descriptors (Manis et al, 2015;Kitsikoudis et al, 2020) and illustrate a direct influence of the density and size of individual shells on wave attenuation. Morris et al (2021) compared the effectiveness of several C. virginica reefs as breakwaters as part of a nature-based coastal protection strategy in a field study on the East Coast of the United States. While the authors conclude that the reef crest elevation is the most important parameter for wave attenuation, they also highlight the dependency of the reef crest to an optimal inundation duration, and thus, to the water level.…”

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

“…Common historic cultch materials are recycled oyster shell, fossilized bivalve shell, or rock. Those basic materials have been used in small-scale, community-based restoration efforts (e.g., [25], or deployed from barges for large-scale restoration efforts [18,26,27]. In the Gulf of Mexico and Chesapeake regions where numerous large-scale restoration efforts have been implemented, shell material became limited and practitioners turned to concrete rubble, mixed rock material, pre-fabricated concrete structures (e.g., Oyster Castles ® , Reef Balls™), or a combination of materials [24,[28][29][30].…”

“…Next, oysters grow out and around the bag as the resulting reef fills in over time. The stacked bags eventually provide a living wave break against erosive wind wave and boat wake energy [25,35]. This plastic mesh is inexpensive, easy to obtain, volunteer-friendly, and has no observed negative impacts on oyster recruitment or other biodiversity associated with oyster breakwaters (e.g., coastal birds, infaua, fishes, mobile and sessile invertebrates, mammals) (e.g., [36][37][38][39]).…”

Strategies for Successful Mangrove Living Shoreline Stabilizations in Shallow Water Subtropical Estuaries

“…The oyster shells within the permeable bags contain biochemical cues which attract oyster larvae to the structure. A "living" breakwater is therefore created over time as more oysters settle and grow on the bags [25][26][27][28].…”