WIXLIB

DukeNICHOLAS INSTITUTENational Ecosystem ServicesPARTNERSHIPEvidence Library for Oyster ReefRestoration in the Gulf of MexicoKatie Warnell, Rachel Karasik, Sara Mason, Alicia Zhao, Shubhi Sharma, Claudia Sandoval1

Evidence Library for Oyster Reef Restoration in the Gulf of Mexicohttp://bit.ly/NI-ESKatie Warnell, Rachel Karasik, Sara Mason,Alicia Zhao, Shubhi Sharma, Claudia SandovalINTRODUCTIONBillions of dollars will be spent on large-scalerestoration of Gulf ecosystems over the comingdecades, but there is no shared platform toguide assessment and reporting of restorationprogress and effectiveness for the broad setof environmental, social, and economic goalsshared by the many institutions working in theGulf. The diversity of these goals—includinghabitat restoration, water quality improvement,marine resource protection, communityresilience, and economic revitalization—means that a variety of metrics are needed tofully evaluate the effectiveness of restorationprojects. The GEMS (Gulf of MexicoEcosystem Service Logic Models and SocioEconomic Indicators) project aims to advancestandardized metrics of restoration successby developing ecosystem service logic models(ESLMs) with stakeholders from the five Gulfstates, relevant federal agencies, and technicalexperts. ESLMs trace the effects of restorationstrategies as they influence ecological andsocial systems to create outcomes that areimportant to people. The use of logic modelsis recommended by the National Academiesof Science as best practice for monitoring plandesign; these models can provide a practicaland transferable approach for measuringsuccess at different scales.information on the GEMS process, see theOyster Reef Restoration Report). The generalESLM is not tied to any particular oyster reefrestoration technique but represents all of theoutcomes from oyster reef restoration thatare dominant—large, tightly linked to oysterreef restoration, and important to the localcommunity. The model shows the cascadeof changes that restoration (dark blue box)causes in the biophysical and social systems(gray boxes), leading to effects on commonlymeasured ecological components (green boxes),human activity outcomes (light blue boxes),and socioeconomic outcomes (yellow boxes).Downloadable pdf and editable versions ofthe general ESLM, as well as specific versionsof the ESLM for each oyster reef restorationtechnique, are available on the GEMS website.The evidence library starting on page fivecontains summaries of the evidence for each ofthe links in the general oyster reef restorationESLM (Figure 1). Summaries include anassessment of the strength of evidence foreach link; links in Figure 1 are color-codedby strength of evidence rating. Each link inthe model has an identification number. Tofind the evidence library entry for a particularlink, you can click on the link number on theconceptual model figure or use the searchfunction (keyboard shortcut Control F) andsearch for “Link #” (e.g., “Link 3”).ECOSYSTEM SERVICE LOGIC MODELFOR OYSTER REEF RESTORATIONThe general ESLM for oyster reef restoration(Figure 1) was developed through a multistepprocess with input from oyster restorationexperts and local stakeholders as wellas through a literature review (for more2

Figure 1. Ecosystem Service Logic Model for Oyster Reef Restoration, Links Color-Coded By Strength of EvidenceRating. Numbers Correspond to Sections Below.3

In the ESLM, pathways consist of links that connect the intervention (left) to a socioeconomicoutcome (right). Major pathways are those where socioeconomic outcomes are tightly linked tooyster reef restoration (ORR) (i.e., there is a possibility that the outcome would show a noticeablechange given an ORR project) (Figure 2). Each link in a major pathway has a moderate to highstrength of evidence rating, is considered attributable to ORR (or has few “Other Factors”), andis considered significant based on the evidence and stakeholder input. We highlight five majorpathways linking the intervention to the following outcomes: Adjacent habitat (which can have a range of additional outcomes and can be exploredthrough the ESLMs for these other habitats); Economic activity in the fishing and oyster harvest industry through oyster harvest(Note: this pathway includes a feedback loop between intermediate outcomes “Oysterpopulation” and “Oyster harvest techniques.” Higher oyster populations in an area canresult in increased harvest limits (or new areas open to harvest) and greater use of oysterharvest techniques. Oyster harvest in turn decreases oyster populations and generateseconomic activity through oyster sales.) Economic activity in the fishing and oyster harvest industry though non-oyster (fish,other shellfish, etc.) harvest; Economic activity through the restoration industry; and Education4

Figure 2. Ecosystem Service Logic Model for Oyster Reef Restoration, Links Color-Coded by Major Pathways.Numbers Correspond to Sections Below.5

EVIDENCE LIBRARY FOR OYSTER REEF RESTORATION ESLMThe evidence for each link in the oyster reef restoration ESLM (Figure 1) is summarized below.Each evidence summary has the following components:Description of RelationshipShort description of the relationship between the starting and ending nodes (boxes), based on theevidence found.Summary of EvidenceOverview of the evidence found to support the relationship, including the types of methods used,geographic location, applicability to the Gulf of Mexico context, and major conclusions.Strength of EvidenceRating of the overall strength of evidence for the relationship, based on the following criteria,with a short explanation.ConfidencelevelCriteriaTypes of evidenceConsistency ofresultsMethodsApplicabilityHighMultipleDirection andmagnitudeof effects areconsistent acrosssources, typesof evidence, andcontextsWell-documented andacceptedHighModerateSeveralSome consistencySome documentation, not Somefully acceptedFairA fewLimitedconsistencyLimited documentation,emerging tPoor documentation oruntestedLimited tononeNoneNoneN/AN/AN/AOther FactorsList of external factors (including biophysical, ecological, and social factors) that influencethe relationship between the starting and ending nodes (boxes), how each factor affects therelationship, and the magnitude of the effect, if known.PredictabilityEvaluation of how predictable a change in the ending node is, given a certain change in thestarting node. For example, the relationship between the two nodes may be unpredictable due toinfluences from external factors or gaps in scientific knowledge. Any models or tools designed topredict the relationship are noted.SourcesList of sources for the evidence for this relationship.6

Link 1: Planting New or Restoring Existing Oyster Reef Oyster Reef Quantity orQualityDescription of RelationshipMost oyster reef restoration projects directly change the quantity or quality of oyster reefs byadding substrate material. Projects aimed at protecting and enhancing existing reefs may addmaterial or protect reefs so that natural processes that cause reef expansion and other attributechanges can occur.Summary of EvidenceThe six oyster reef restoration techniques considered in this project represent four majorcategories in terms of their effect on oyster reef quantity or quality; these four categories areaddressed separately in this summary.Placement of oyster substrate to create structurally simple reefs (Technique 1): These projectsplace loose cultch material (usually oyster shells, relic shells, crushed limestone, or crushedconcrete) on the estuary floor to create a flat or “two-dimensional” structure on which oysterscan grow. Monitoring reports from oyster restoration sites in Louisiana and Florida confirm thatcultch placement projects increase the extent of oyster substrate (Louisiana Natural ResourceTrustees 2016, NRDA 2017). However, these reefs are designed to recruit a single age class ofoysters; when these oysters are harvested, the majority of oysters on the reef are removed andthe reef structure is substantially damaged (for more detail on the effects of harvesting on oysterreef quantity and quality, see Link 29). Field research and modeling show that low reefs exposeoysters to poor environmental conditions, resulting in a less healthy oyster community, and aresusceptible to burial by sediment, decreasing their long-term viability (Jordan-Cooley et al. 2011;Schulte et al. 2009).Placement of oyster substrate to create structurally complex reefs (Techniques 2, 3, and 4): Theseprojects place large, durable materials (e.g., oyster balls, precast concrete structure, large piecesof limestone) to create a three-dimensional structure to which oysters can attach. The resultingoyster reef has a significant vertical component, resulting in a healthier oyster community due toexposure to better environmental conditions, and is less likely to be buried by sediment (JordanCooley et al. 2011; Schulte et al. 2009). These projects can be placed in subtidal or intertidal areasand can be open or closed to harvest (see Link 29 for discussion of harvesting effects on oysterreef quantity and quality). Metrics related to reef height and structural complexity are not oftencollected or made available, making it difficult to assess the long-term influence of projects onreef quantity and quality (La Peyre et al. 2014; Appendix A). A field survey of subtidal oysterrestoration projects in the Gulf of Mexico found that rock reefs had greater volumes (liters/m2,indicating higher vertical relief or more complexity) than shell or historic reefs (La Peyre et al.2014). Intertidal projects, often referred to as “living shoreline” projects, often use vertical relief ofthe reef as a key monitoring metric (e.g., NOAA Restoration Center 2016).Protection or enhancement of existing reefs (Technique 5): Protection of existing reefs(preventing intensive oyster harvest) does not directly change reef extent or structure. Dependingon system dynamics (including oyster growth rates, disease, and other stressors), protectedreefs may accumulate material and grow in extent, height, and complexity. An analysis of oysterstock assessment data in the Delaware Bay estimated the minimum doubling time of oyster shellmaterial on oyster beds at 10–25 years, assuming zero shell loss (Powell et al. 2006). This indicatesthat oyster reefs can grow naturally when shell loss (caused either by environmental conditions or7