This project team will determine the most cost-effectiveness means of nursery production to improve oyster reef aquaculture and restoration while working with oyster farmers and training future scientists. The team will develop a new hatchery technique to expose oysters to predator cues and produce oysters with thicker shells, which increases their survival and marketability for both the seafood market and reef restoration. The research team also will conduct a cost-benefit analysis of different methods of spat-on-shell restoration.

Objectives

Oyster populations have declined substantially in Mississippi and Alabama. To combat oyster loss and recover lost ecosystem services from oyster reefs, state agencies in Mississippi and Alabama have initiated remote setting operations whereby oyster larvae are settled onto cultch and then placed onto existing reefs for fisheries enhancement. Additionally, off-bottom farming of oysters for the half-shell market is also being used to boost oyster production. Yet, both remote setting and off-bottom farming are plagued by mortality for predators. Preliminary results suggest that exposing oysters to predator exudates in the nursery following settlement causes oysters to develop thicker, stronger shells that are resistant to predation and increase oyster survival. Further, thicker shelled oysters may be more valuable due to their shell aesthetics.

The purpose of this research is to develop a new hatchery technique that produces oysters with thicker shells that increases their survival and marketability for aquaculture and reef restoration by exposing oysters to cues from predators in a nursery. Specifically, this research will:

1. Increase oyster reef locations restored with spat-on-shell to determine field conditions where this technique is most useful.
2. Use diploid and triploid seed oysters to determine if using predator cues will improve survival and marketability of off bottom oyster farming.
3. Conduct a cost-benefit analysis to assess the most cost-effective methods for spat-on-shell restoration.
4. Expand workforce development by including high school students in research.

Methodology

Oysters are spawned in a hatchery and then either settled on sun-bleached oyster shells or other cultch to become spat-on-shell or settled onto microcultch to grow as singles or seed oysters that are farmed for the half-shell market. Spat-on-shell are kept in the nursery for 2 weeks prior to field placement while seed oysters remain in the nursery until the exceed 2 mm, which usually takes ~3 weeks. Preliminary studies using spat-on-shell revealed that exposing oysters to predator cues and holding them in the hatchery for 4 weeks increased oyster shell hardness and survival. Similarly, seed oysters grow stronger shells when exposed to predators, although the effects on seed oyster survival when grown off-bottom have not been investigated. Here, we will expose both spat-on-shell and seed oysters to predator cues from blue crabs. Spat-on-shell will be held in the nursery for either 2 weeks as this is standard practice or for 4 weeks because we know that this time improves survival significantly. Seed oysters will remain in the nursery until reaching 2mm as industry standard. Before placement in the field, shell strength and size will be measured. Oyster growth and survival will be monitored at regular intervals for 12 months, and then oysters will be assessed for size, fecundity, soft tissue amount and quality, and shell aesthetics to determine the effects of nursery rearing technique on these factors. A cost-benefit analysis will be conducted to ascertain if using predator cues and/or longer holding times for spat-on-shell improves return on investment for oyster restoration and aquaculture. Part of this work will be performed on an oyster lease operated by high school students in the Alma Bryant Aquaculture Program, and their participation in this project will increase work force development.

Rationale

For over a century, commercial oyster harvesting has been a fundamental component of the economy and culture of Gulf coast states. Yet, Mississippi and Alabama have experienced astonishing deteriorations in the oyster fishery and subsequent ancillary benefits oyster provide. To restore reefs and boost production levels, local businesses, academia, and state agencies have invested heavily in remote setting for oysters as either spat-on-shell for placement on bottom to boost natural reefs or as seed oysters to be farmed off-bottom. We are proposing to investigate an inexpensive technique that may drastically improve return on investment for oyster restoration and aquaculture.