Oyster reef restoration: substrate suitability may depend on specific restoration goals

Abstract

A limited supply of oyster shell for restoration practices has prompted investigations of alternative substrates used in construction of artificial oyster reefs. The success of oyster reef restoration projects is increasingly focused not only on oyster densities, but also on habitat provisioning for associated fauna. A subtidal oyster reef complex (0.24 km2) was restored in the Mission‐Aransas Estuary, Texas, U.S.A., in July 2013 using replicated mounds of concrete, limestone, river rock, and oyster shell substrates. Oyster and reef‐associated fauna characteristics were quantified quarterly for 15 months, using sampling trays that were deployed 3 months after construction. The highest densities of oyster spat occurred 9 months after tray deployment (July 2014, 1,264/m2), whereas juvenile oyster densities increased throughout the study period to 283/m2. Concrete (1,022/m2) and limestone (939/m2) supported the highest number of oysters over all dates. Oyster shell (1,533/m2) and concrete (1,047/m2) substrates supported the highest densities of associated motile fauna. Faunal diversity (Hill's N1) did not vary by substrate material, but did show seasonal variation. A simple benefit–cost ratio was used to indicate the localized monetary value for each of the substrates. Oyster shell and concrete substrates returned the highest benefit–cost ratio for motile fauna, while concrete yielded the highest benefit–cost ratio for oyster abundance. Incorporating benefit–cost ratios in restoration planning will allow practitioners to better integrate substrate‐specific ecological values with economic considerations and project goals to maximize return on restoration investments.

Mimicry of emergent traits amplifies coastal restoration success

“…At present, erosion is an increasing problem along coastlines in general, and at degraded sites that require restoration in particular 36 . To combat this pervasive challenge, hard structures from shells or concrete are often applied to provide stable substrates necessary to stimulate reef formation [37][38][39][40][41][42][43] , while sediment stabilization measures have been used to support vegetation establishment 44,45 . Our approach builds upon these efforts by experimentally demonstrating that tailor-made mimicry of species-specific key emergent traits-identified from past ecological studies-facilitates the establishment of different habitat-forming species.…”

Rapid development of a restored oyster reef facilitates habitat provision for estuarine fauna

“…Indeed, densities were 2× higher than on the reportedly largest reestablished metapopulation of oysters globally (overall mean: 1027 ± 52 n/m 2 in a Chesapeake Bay sub‐estuary; Schulte et al ). In the Gulf of Mexico, Graham et al () reported mean oyster densities of 1,023 and 939 n/m 2 on restored reefs constructed using concrete and limestone substrates, respectively. In a related study, short‐term (4 month) field deployments of substrates resulted in spat densities of 1,242–1,513 and 929–1,447 n/m 2 on concrete and limestone, respectively (George et al 2015).…”

“…Limestone and concrete have been demonstrated as successful substrates for oyster reef restoration along the U.S. Gulf and Atlantic coasts (Soniat et al1991; Soniat & Burton ; Brumbaugh ; LDWF ; George et al 2015; Graham et al ). In the current study, substrate type was not an important factor influencing oyster population development or faunal community composition.…”

“…Oyster reef restoration has become a principal strategy for increasing provision of ecosystem services and enhancing biodiversity (Grabowski et al ). A number of standard restoration principles have been identified for faunal recruitment and habitat utilization, including the importance of vertical relief (Lenihan ; Gregalis et al ; Schulte et al ), structural complexity (Humphries et al ; Karp et al ), and substrate selection (Soniat et al ; Brumbraugh 2000; Soniat & Burton ; Nestlerode et al ; George et al 2015; Graham et al ). These tenets have advanced reef restoration by guiding restoration actions that contribute most to the reestablishment of desirable characteristics within a project area.…”

Concrete Durability Probed Using Compressive Strength, Chloride Penetration and Porosity Measurements on CEMII and CEMV Concretes Incorporating Mollusc Shell Spares in Artificial and Natural Seawaters

“…A substitution of 20% of the aggregates (D4/10) by oyster shell aggregates was made to study the effect of this biomineral by-product on the recruitment of oyster larvae. Indeed, the incorporation of mollusc shell aggregates can increase the bioreceptivity of concrete because they provide an ideal substrate for the settlement of marine organisms (Graham et al, 2017;Hanlon et al, 2018). After the characterization of the raw materials, concrete mix designs formulation was carried out in accordance with EN 206-1.…”