The Oyster is Your World

Eastern oysters are well known ecosystem engineers responsible for water filtration, providing habitat and refuge for numerous species, and other ecosystem services. However, natural oyster reefs are declining due to several natural and anthropogenic threats. To mitigate for the loss of natural oyster reefs, many reef restoration projects have been completed and several more are being planned. It is known that variation in reef height, interstitial space, and slope can encourage oyster settlement, but little is known about how reefs can be designed to exclude predation of oysters by oyster drills, fish, crabs, and other predators. In this study, we seek to quantify the effectiveness of varying oyster reef designs at excluding predation. Four replicates of six different reef designs varying interstitial space and lower reef gastropod obstacles have been created from Portland cement and baited with adult oysters. These reef units were tested in a mesocosm setting in Biloxi, MS. Daily monitoring of the location of oyster drills on the reef and oyster mortality were recorded. Results from this study can be used to inform the design of oyster reef restoration projects.

Oysters are a focus for many coastal restoration projects; however, little information is known about habitat preferences for one of their primary predators (oyster drills). Oyster drills (Stramonita haemastoma complex) are recognized as significant oyster predators, posing a threat to oyster populations as well as the success of conservation and restoration efforts using oysters, such as living shorelines. Drill abundance is known to be influenced by salinity, with a preference for higher salinities; however, information on other habitat preference factors is limited. In this study, the impact of substrate type and oyster presence on oyster drill abundances along the coastal regions of Mississippi and Alabama was assessed. Four sites, paired with controls, were used that included a combination of sites with oysters present or absent and either fine or coarse sediment. Oyster drill abundances were quantified using baited traps deployed parallel to the shoreline every four weeks between May and October 2023. Statistical analyses revealed significant differences in oyster drill abundances among sites, with coarse sediment sites exhibiting higher abundances. However, oyster presence did not significantly influence drill abundances. These findings suggest factors other than salinity and oyster presence, such as sediment type, may drive oyster drill abundances. Understanding these factors is crucial for informing coastal restoration efforts and management of oysters.

Over the past decade, Mississippi Sound has been subjected to profound interannual variation in Mississippi River inflows that have led to the most active application of human managed diversions as well as interventions intended to inhibit saltwater intrusions threatening upstream freshwater supplies. As a means of assessing large-amplitude interannual variations in riverine flows affecting the living marine resources of the Mississippi Gulf Coast, the University of Southern Mississippi modeling group has applied a 400 m resolution, 24-layer circulation model of the Mississippi Sound and Bight (msbCOAWST), which utilizes the Coupled Ocean Atmosphere Wave Sediment Transport modeling system. Our model is designed to support the coastal management community, providing the tools and resources needed to better evaluate complex scientific issues and inform natural resource management decisions. msbCOAWST has been designed to explicitly include riverine diversion constructs, both extant and proposed, that affect the estuarine and shelf waters of the MS Sound/Bight. Here, we apply our modeling framework to characterize how the hydrodynamic environments resulting from the unprecedented repeat openings of the Bonnet Carré Spillway (2018-2020) contrast with the hydrodynamic conditions resulting from the reduced river inflows of recent years. Within this context, the climatological (i.e., business as usual) solution is used as further context for assessing the degree to which the recent interannual trend holds promise for reestablishing the MS Sound's shellfishery.

The main focus of this study is to understand the bi-weekly and seasonal variability of circulation and salinity under extreme freshwater inflow conditions, focusing on experimental oyster leases near Saint Louis Bay (SLB) and Pascagoula Bay (PB) to guide oyster reef restoration efforts in the Mississippi Sound (MSS). Two-way-nested hindcast (2019) simulations in a regional MSS and Bight application of the Coupled Ocean Atmosphere Wave Sediment Transport modeling system were setup using high-resolution nested grids. Oyster lease areas are affected differently under high and low freshwater inflow conditions depending on the mean circulation variability at SLB and PB regions in response to the combined effects of different forcings. Results indicate that north-eastward currents dominate the circulation both in surface and bottom layers on bi-weekly scale near SLB in Western MSS from mid-March to mid-July because of higher barotropic pressure associated with the Bonnet Carré Spillway (BCS) openings and multiple peak discharges in Pearl River. Episodic events, i.e., BCS closing in April and Hurricane Barry in July, affect the circulation on bi-weekly scale by decreasing the current intensity and increasing the salinity, especially in the bottom layer. The opposite bi-weekly mean surface current is observed in spring in Eastern MSS near PB due to westward wind component and high barotropic pressure caused by peak discharges in Mobile River from March until the current reversal due to BCS re-opening in May. Our analysis reveals the collective controlling effects of winds and freshwater inflow upon the mean circulation patterns within SLB and PB regions. A deeper understanding of spatial and temporal variability of the circulation in MSS using high-resolution nested ocean models allows us to better understand the water quality variability which is crucial for maintaining the viability of oyster reefs.

Oyster resources have rapidly declined in Mississippi waters in recent years. Over the past two decades, devastating declines occurred due to Hurricane Katrina (2005), the Deepwater Horizon Oil Spill (2010) and openings of the Bonnet Carré spillway (2011, 2019) to divert flood waters of the Mississippi River from New Orleans and surrounding areas. Extended discharge through the Bonnet Carré spillway in 2019 completely decimated adult oyster stocks, and commercial harvests have not occurred within western Mississippi Sound since 2018. A collaboration between USM and ERDC offers an opportunity to address management questions related to the vulnerable oyster reef ecosystem in Mississippi Sound using a recently completed experimental reef plot system consisting of four 50-acre reef sites, two each in western and eastern Mississippi Sound. At each site, six base reefs constructed within one-acre plots were created from #4 limestone rock. Two additional plots at each site serve as non-reef controls. One site each within the western and eastern Sound was completed in two phases, the first in March and the second in June/July of 2024. The hierarchical layout of the experimental reef plot system enables investigations at multiple spatial scales with proper replication. The reefs can serve as a testing ground for tracking oyster recovery, restoration experiments, and harvesting methods, and will permit at-scale comparisons of alternative methods of cultivation practices for on-bottom leaseholders. Results from experiments will ideally inform management and end users of the costs and benefits of alternative rearing and harvesting practices based on oyster performance metrics like production and survival, as well as positive effects as habitat for the Gulf sturgeon and other beneficial fishes, thereby contributing to the formulation of management guidelines.

In recent years, the integration of heavy-lift agri-drones into environmental restoration projects has shown significant promise, particularly in the field of oyster restoration. AquaTech Eco Consultants, with over 25 years of experience in coastal mitigation and restoration, has pioneered the use of these drones to enhance the viability and efficiency of restoration efforts. This presentation will explore the innovative application of heavy-lift agri-drones in deploying oyster seeds in estuarine environments.
Estuaries, often referred to as the "nurseries of the sea," are critical ecosystems that support a diverse range of marine life and contribute significantly to the national economy. However, these ecosystems are under threat from rising pH levels, increasing water levels, and decreasing salinity. To combat these challenges, AquaTech has collaborated with local non-profits, universities, and restoration aquaculture facilities to develop and implement advanced drone technology for oyster restoration.
The presentation will highlight a case study in Apalachicola Bay, where AquaTech successfully deployed 36 million oyster seeds using agri-drones. This project demonstrated the drones' ability to deploy seeds precisely and efficiently, significantly improving the restoration process. The use of drones has also brought socio-economic benefits, increasing public awareness of environmental issues and providing new revenue opportunities for local farmers.
By showcasing the successful integration of drone technology in environmental restoration, this presentation aims to inspire further innovation and adoption of advanced technologies to preserve and restore vital estuarine ecosystems.

Oyster farming, particularly in the Gulf of Mexico, has witnessed significant expansion with the adoption of off-bottom culturing techniques. The vulnerability of floating cage oyster farms to severe weather events such as hurricanes remains a crucial concern. Existing knowledge of storm preparedness is often based on anecdotal evidence, lacking a science-based approach tailored to floating oyster farm's infrastructure failure caused by wind, waves, currents, and fluctuating sea level. This encompasses the establishment of a comprehensive infrastructure assessment system for oyster aquaculture. Based on an open-source computational fluid dynamic program and up-to-date hydrodynamic modeling approaches, we develop a three-dimensional fluid-structure-mooring model for floating oyster aquaculture that enables realistic resistance evaluations against extreme conditions. At the cage level, the model considers the intricate arrangement of floats, cage and bag wires, and randomly packed oyster shells to estimate the environmental load on a single cage. At the farm level, the model resolves the interaction between multiple bodies, fluid dynamics, and flexible constraints are to better estimate the mooring load. Through meticulous scenario studies, the infrastructure integrity at multiple operation states (normal floating, flip-over, and bottom-sinking) under extreme conditions are investigated. After validated with flume experiments, the modeling system will be applied to study infrastructure resilience of realistic floating oyster farms in the Mobile Bay-Mississippi Sound area. The outcomes will provide practical recommendations to minimize economic losses and enhance farm design. By collaborating with aquaculture business specialists and stakeholders, the research outcomes are disseminated to the wider community, contributing to the enhancement of oyster farm infrastructure.