EXAMINING IN SITU SETTING OF OYSTERS IN A SHALLOW TEXAS BAY

In Texas, oyster reef restoration has only occurred through addition of substrate, including oyster shell, clam shell, rock, or a mixture of these, (e.g., Goose Island State Park in Mission-Aransas Bay http://oysterrecycling.org/).  Substrate addition has been relied upon in Texas, as oyster larval supply is not considered to limit recruitment in the region. However, catastrophic natural (i.e., rainfall) or human-induced (i.e., chemical/oil spill) events can decimate a cohort that may take years to redevelop, especially if repeated catastrophic events occur, such as seen with the 2015 and 2016 excessive spring rains in Texas.  Therefore, there is a need to develop direct restoration methods where larval supply may be limited or there is a need to "jump start" a local population.

Common effective methods to restore oyster reefs include placing oyster seed (i.e., hatchery-produced oysters usually >10mm shell height) on a reef or seeding substrate with oysters (i.e., allowing settlement of larvae onto substrate) before deployment.  Spat-on-shell is one form of seeded substrate.  Shell with spat (<1mm height) is then transported to the site for placement.  Unfortunately, multiple handlings during transport may result in crushed spat and reduced oyster survival.  Additionally, as substrate traditionally used in remote setting (e.g. oyster and clam shell) becomes more scare, other substrates are being utilized at oyster restoration sites.  Costs for both acquiring shell, as well as seeding and subsequently transporting novel substrates, will likely grow, thus reducing logistical and economic benefits of applying remote setting methods to restore reefs.

Alternate methods for direct restoration are the use of larvae release and in situ setting.  Larval release takes newly fertilized eggs or early D-larvae and releases them into the waterways as if they were spawned in the area.  This requires an excessive number of larvae added to make up for natural mortality (e.g., unfavorable advection, predation, starvation).  In situ setting, which is a form of remote setting, takes only competent larvae (i.e., larvae that are ready to metamorphose and settle) to the site and places them in enclosed areas for settlement on natural or deployed substrate.  This method has shown to produce setting efficiencies (spat produced per larvae added) comparable to traditional remote setting techniques, however, in situ (or direct) settlement methods need refinement to increase efficiency and universal applicability.

Therefore, the objectives of our research are to: 1) compare two substrates for successful settlement and survival from in situ setting, 2) determine if there is a seasonal effect on successful settlement and survival from in situ setting, 3) provide a cost analysis for an in situ setting protocol, and 4) conduct a workshop for stakeholders on in situ setting methods for restoration efforts in Texas.  Project support is from DOC/NOAA award (NA18OAR4170088) to TX Sea Grant and subaward (M1801874) to TAMU-CC.