Developing a decision-making guide for oyster restoration practices

Abstract

This proposal seeks to improve sustainable fisheries and aquaculture by investigating the suitability of restoration sites in Mobile Bay, AL to develop a cultch suitability map and to determine what strategy should be implemented to maximize the likelihood that a restored reef will become established. Results will directly benefit planned oyster restoration projects led by the Alabama Department of Conservation and Natural Resources (ADCNR) and The Nature Conservancy. Numerous factors may hinder oyster restoration efforts such as insufficient recruitment, hypoxia and predation. Different techniques may be used to overcome these challenges. For example, placing restored reefs intertidal may reduce hypoxia exposure and lower predation, and using spat-on-shell can help rebuild oyster reefs in areas of low recruitment. The survival of spat-on-shell can be significantly improved by exposing it to predator cues prior to placement in the field and using cages to reduce predator access. Recent studies suggest shading intertidal oysters can alleviate temperature stress. These techniques require significantly more time and resources than cultch planting alone, but may be necessary in areas with low recruitment, high predation or hypoxic conditions. The proposed work involves creating experimental oyster reefs using different techniques deployed in a block design to determine 

• If an area is suitable for oyster restoration.
• Which techniques are the most cost effective for restoring oysters at that location. 

We have been collaborating with Alma Bryant High School for assistance with spat-on-shell rearing and deployment, and we will
continue to work with them to pursue our goal of workforce development. We also work with Mobile Baykeeper and citizen
scientists to assist with spat-on-shell rearing.

Objectives

• Use a recently developed adaptive management decision making guide for oyster restoration and test its use while creating experimental oyster reefs.
• Collaborate with ADCNR to determine best methods for oyster reef restoration at a potential restoration sites using adaptive management guide.
• Quantify costs for different oyster restoration techniques and refine decision-making guide.
• Continue collaboration with Alma Bryant High School to involve their students in research projects and provide training for workforce development.

Methodology

We will construct experimental oyster reefs built using cultch (plain oyster shells), spat-on-shell, or spat-on-shell that was reared with predator cues to make oyster shells harder and place those at 20 locations in coastal Alabama. These three treatments will either be secured using wire mesh or left unsecured, which creates 6 treatments that will be placed in an experimental block. Oyster survival and growth will be monitored for 15 months to determine which areas and techniques are best for oyster restoration.

Rationale

Oysters provide many benefits, but their populations have declined precipitously throughout Mobile Bay, prompting numerous oyster restoration efforts. Historically, Denton Reef in Western Mobile Bay had considerable oyster reef habitat that was popular with recreational fishermen and sustained nearby reefs, but oysters in this area have largely disappeared. The Alabama Department of Conservation and Natural Resources (ADCNR) will restore oysters in Mobile Bay and Mississippi Sound to supply oyster larvae to nearby harvested reefs, to recover lost ecosystem services (e.g., water filtration), and to improve recreational fishing. In recruitment limited areas, using remote setting can improve restoration outcomes by breeding and settling juvenile oysters onto shells prior to the substrate’s placement in the field (aka spat-on-shell). Oysters harden their shells when detecting exudates from predators. Exposing spat-on-shell to predator cues prior to placement can increase survival. This approach may be needed in areas with high predation pressure. Finally, waves can displace loose oyster shells and, securing shells via wire cages may be needed to promote reef development. The purpose of this study is to test an Adaptative Management Decision Making Guide that ADCNR and other entities can use to select the most cost-effective means to restore oyster populations. Using this guide, we will determine which approach is most cost efficient for this site. We will also structure the guide to be quantitative (e.g., differences in dollars invested per gains in reef health) so it can inform future restoration efforts.