Combining ecology and technology to kick‐start oyster reef restoration

OnlinePublTechniques that enhance the recruitment of foundation species to restoration sites can inform the ecological development of the restored habitat. However, techniques are often considered in isolation, potentially overlooking synergies from combining them. Native oyster reefs have been lost worldwide, resulting in restoration efforts in systems that are often recruitment limited, or where recruiting oysters must spatially compete with opportunistic species. Here, we present a field-based study that combines ecological knowledge on positive species interactions with novel acoustic technology, both of which are demonstrated to boost oyster recruitment in isolation, to test whether their interaction synergistically enhances the early larval recruitment that drives oyster reef development. At three sites across a 20 ha oyster reef restoration in southern Australia, we used self-made speakers to broadcast healthy reef soundscapes that attract oysters and combine this with artificial kelp that facilitates oyster recruitment by suppressing competitive species (turfing algae). The combination of acoustic enrichment and artificial kelp increased oyster recruitment to the topside of substrate (326.98%increase), whereas only acoustic enrichment increased recruitment to the underside of substrate (126.95% increase). Our findings suggest that the combination ofmultiple techniques and their interactive effectsmight boost the early stages of reef development, providing proof-of-concept that these approaches can help oysters to build and bind reefs (i.e. recruit to the topside and underside, respectively). By combining ecology with technology during the first stages of a developing reef restoration, we show the potential value of these novel approaches to kick-start the recovery of lost oyster reefs.Brittany R. Williams, Dominic McAfee, Sean D. Connel

Oyster larvae swim along gradients of sound

First published: 04 May 20221. Marine soundscapes provide navigational information for dispersing organ-isms, but with wide-scale habitat loss, these soundscapes are becoming muted. Consequently, dispersing larvae that use soundscapes for navigation may be lost at sea, limiting the success of restoration efforts that rely upon the recruitment of dispersing organisms to restore habitat. Where limited larval supply constrains restoration efforts, using speakers to create gradients in healthy soundscapes could provide the navigational cue that attract larvae and enhances recruitment.2. Combining laboratory and field studies, we test whether broadcasting soundscapes might act as a directional cue for oysters targeted for national-scale reef restoration; the Australian flat oyster Ostrea angasi. In the laboratory, we tested whether settlement of larvae increases along a gradient of increasing sound in-tensity (8 m laboratory tank) versus a no sound control, and whether settlement increases with soundscapes that approximate healthy reefs.3. In the field, we tested the context dependency and magnitude of using boosted soundscapes for restoration practice in areas of low, medium and high back-ground noise, by observing the settlement rates of naturally recruiting oysters at three restoration sites when exposed to boosted reef sound relative to ambient conditions.4. In the laboratory, we showed that 83% of larvae swim horizontally towards reef sound to settle in greater densities closer to its source, a near doubling of the larvae (44%) that dispersed in the no sound controls. Larval settlement increased by 300% in the presence of reef sound relative to controls in the laboratory. In the field, speakers increased larval settlement in localities of lower background noise. To our knowledge, this is the first evidence that oyster larvae can swim horizontally and choose to move towards a sound source.5. Synthesis and applications. We discovered that oyster larvae can swim horizon-tally towards reef sound and then settle in higher densities, relative to controls. Importantly, this effect of sound on recruitment is enhanced in localities of lower background noise. We propose that where recruitment is limited, restoration practitioners best use acoustic technology in localities of lower background noise to guide larvae to boost recovery.Brittany R. Williams, Dominic McAfee, Sean D. Connel

Repairing recruitment processes with sound technology to accelerate habitat restoration

Humanity's ambitions to revive ecosystems at large scales require solutions to move restoration efforts beyond the small scale. There are increasing calls for technological solutions to reduce costs and facilitate large-scale restoration through use of emerging technologies using an adaptive process of research and development. We show how technological enrichment of marine soundscapes may provide a solution that repairs the recruitment process to accelerate the recovery of lost marine habitats. This solution would solve the problems of current practice that largely relies upon natural recruitment processes, which carries considerable risk where recruitment is variable or eroded. By combining the literature with laboratory experiments, we describe evidence for 'highways of sound' that convey navigable information for dispersing life-stages in search for adult habitat. We show that these navigational cues tend to be silenced as their habitat is lost, creating negative feedbacks that hinders restoration. We suggest that reprovisioning soundscapes using underwater technology offers the potential to reverse this feedback and entice target organisms to recruit in greater densities. Collective evidence indicates that the application of soundscape theory and technology may unlock the recruitment potential needed to trigger the recruitment of target organisms and the natural soundscapes they create at large scales.Brittany R. Williams, Dominic McAfee and Sean D. Connel

Evaluation of constraint methodologies applied to a shallow-flaw cruciform bend specimen tested under biaxial loading conditions

A technology to determine shallow-flaw fracture toughness of reactor pressure vessel (RPV) steels is being developed for application to the safety assessment of RPVs containing postulated shallow surface flaws. Matrices of cruciform beam tests were developed to investigate and quantify the effects of temperature, biaxial loading, and specimen size on fracture initiation toughness of two-dimensional (constant depth), shallow surface flaws. The cruciform beam specimens were developed at Oak Ridge National Laboratory (ORNL) to introduce a prototypic, far-field. out-of-plane biaxial stress component in the test section that approximates the nonlinear stresses resulting from pressurized-thermal-shock or pressure-temperature loading of an RPV. Tests were conducted under biaxial load ratios ranging from uniaxial to equibiaxial. These tests demonstrated that biaxial loading can have a pronounced effect on shallow-flaw fracture toughness in the lower transition temperature region for RPV materials. The cruciform fracture toughness data were used to evaluate fracture methodologies for predicting the observed effects of biaxial loading on shallow-flaw fracture toughness. Initial emphasis was placed on assessment of stress-based methodologies. namely, the J-Q formulation, the Dodds-Anderson toughness scaling model, and the Weibull approach. Applications of these methodologies based on the hydrostatic stress fracture criterion indicated an effect of loading-biaxiality on fracture toughness, the conventional maximum principal stress criterion indicated no effect

An interim report on shallow-flaw fracture technology development

Shallow-flaw fracture technology is being developed for application to the safety assessment of radiation-embrittled nuclear reactor pressure vessels (RPVS) containing flaws. Fracture mechanics tests on RPV steel, coupled with detailed elastic-plastic finite-element analyses of the crack-tip stress fields, have shown that (1) constraint relaxation at the crack tip of shallow surface flaws results in increased data scatter but no increase in the lower-bound fracture toughness, (2) the nil ductility temperature (NDT) performs better than the reference temperature for nil ductility transition (RT{sub NDT}) as a normalizing parameter for shallow-flaw fracture toughness data, (3) biaxial loading can reduce the shallow-flaw fracture toughness, (4) stress-based dual-parameter fracture toughness correlations cannot predict the effect of biaxial loading on shallow-flaw fracture toughness because in-plane stresses at the crack tip are not influenced by biaxial loading, and (5) a strain-based dual-parameter fracture toughness correlation can predict the effect of biaxial loading on shallow-flaw fracture toughness

Development of a shallow-flaw fracture assessment methodology for nuclear reactor pressure vessels

Shallow-flaw fracture technology is being developed within the Heavy-Section Steel Technology (HSST) Program for application to the safety assessment of radiation-embrittled nuclear reactor pressure vessels (RPVs) containing postulated shallow flaws. Cleavage fracture in shallow-flaw cruciform beam specimens tested under biaxial loading at temperatures in the lower transition temperature range was shown to be strain-controlled. A strain-based dual-parameter fracture toughness correlation was developed and shown to be capable of predicting the effect of crack-tip constraint on fracture toughness for strain-controlled fracture. A probabilistic fracture mechanics (PFM) model that includes both the properties of the inner-surface stainless-steel cladding and a biaxial shallow-flaw fracture toughness correlation gave a reduction in probability of cleavage initiation of more than two orders of magnitude from an ASME-based reference case

Preliminary assessment of the effects of biaxial loading on reactor pressure vessel structural-integrity-assessment technology

Effects of biaxial loading on shallow-flaw fracture toughness were studied to determine potential impact on structural integrity assessment of a reactor pressure vessel (RPV) under pressurized thermal shock (PTS) transient loading and pressure-temperature (PT) loading produced by reactor heatup and cooldown transients. Biaxial shallow-flaw fracture-toughness tests results were also used to determine the parameter controlling fracture in the transition temperature range, and to develop a related dual-parameter fracture-toughness correlation. Shallow-flaw and biaxial loading effects were found to reduce the conditional probability of crack initiation by a factor of nine when the shallow-flaw fracture-toughness K{sub Jc} data set, with biaxial-loading effects adjustments, was substituted in place of ASME Code K{sub Ic} data set in PTS analyses. Biaxial loading was found to reduce the shallow-flaw fracture toughness of RPV steel such that the lower-bound curve was located between ASME K{sub Ic} and K{sub IR} curves. This is relevant to future development of P-T curve analysis procedures. Fracture in shallow-flaw biaxial samples tested in the lower transition temperature range was shown to be strain controlled. A strain-based dual-parameter fracture-toughness correlation was developed and shown to be capable of predicting the effect of crack-tip constraint on fracture toughness for strain-controlled fracture