A Commercial Hatchery's Perspective on Biosecure Seed Transfer to the Gulf

Moving Oysters,  Supporting Economies, and Protecting Ecosystems

Oyster aquaculture supports local economies, provides a sustainable food source, and offers ecosystem services such as habitat creation and improved water quality. Hatcheries raise oyster larvae and seed to support farmers and ongoing restoration projects. Larvae and seed are frequently shipped across state lines for these purposes, so it is important to transfer them carefully. The transfer process isn’t just about logistics, it is also about biosecurity – a set of best practices that keep pathogens and invasive species from hitching a ride. 

What Biosecurity Means in Oyster Aquaculture 

Biosecurity protects both farmed and wild populations by preventing the spread of shellfish specific diseases. Oysters from one region can sometimes carry naturally occurring diseases that are not established in other areas. Some pathogens that are common in one region, such as Haplosporidium nelsoni that causes MSX-disease in the Atlantic, may not be present in another region, e.g., the Gulf of Mexico. Other pathogens, such as Perkinsus marinus that causes Dermo-disease, extend across regions that have different genetic strains (e.g., Atlantic vs Gulf). An oyster’s ability to tolerate disease is partly determined by its genetics. Local oyster populations may struggle when exposed to unfamiliar or non-native strains of pathogens. For example, oysters from the Atlantic may not have the same level of tolerance to Gulf-specific pathogen strains or vice versa. Therefore, oyster genetics becomes a consideration for larvae and seed transfer as well.

For a number of years, the Regional Shellfish Seed Biosecurity Program (RSSBP), a collaborative group of industry, scientists, regulators, and extension, co-founded by Rutgers University and Virginia Institute of Marine Science, has been running a hatchery certification program “to streamline the process of permitting interstate commerce of biosecure hatchery shellfish seed and to promote best practices to maintain biosecurity in shellfish hatcheries.”  OSH was a founding participant in the hatchery certification program and has remained a participant since its inception. Thanks in part to the function of this program, there is a track record of pathology screenings from hatcheries up and down the east coast produced as part of the seed importation process. In these pathology screenings, and other research studies conducted by shellfish pathologists, there has been very little detection of pathogens in small seed, say 1-2mm in size, and no observation of actual infection in these seed. Therefore, there is high confidence along the US Atlantic Coast in transferring biological material across state lines. The case for larvae is even stronger, with no known detection of pathogens or observation of infection in oyster larvae. 

These clean bills of health are a combination of water treatment practices within the hatchery that are very effective at excluding these pathogens from the water, and the theory that seed this small may not even be able to pump enough water to amass enough pathogen cells to cause infection. 

Why it Matters in the Gulf

Hatchery production of seed in the Gulf—essential to that region's shellfish aquaculture industry—has faced supply challenges. The industry faces a classic catch-22 of developing shellfish aquaculture: industry growth is limited because of hatchery seed undersupply, and development of new hatcheries is limited by lack of demand. Being able to move seed from Atlantic suppliers to Gulf markets might be a way out of this seed-limited conundrum. While biosecurity testing has advanced considerably over the past decade, restrictions on importing larvae and seed from the Atlantic to the Gulf remain. These restrictions reflect valid concerns about the potential introduction and spread of disease, given the complex and sometimes unpredictable nature of pathogen dynamics in marine systems. OSH has been active in assuring and evaluating our own biosecurity through research and development and are actively investigating  the potential for a safe and bio-secure transfer of seed from the Atlantic to the Gulf.

Biosecurity R&D in 2023 at OSH: larvae

Our first Gulf biosecurity project was self-funded during the 2023 hatchery season with the goal of demonstrating bio-secure transfers of oyster larvae to a secure facility in the Gulf. 

During three separate spawning sessions, larvae from both Gulf and Virginia broodstock were produced. When larvae reached the pediveliger stage, a sample from each cohort was sent for disease screening to the Virginia Institute of Marine Science Shellfish Pathology Lab (VIMS SPL). Most of the rest of the pediveliger larvae from each cohort were then sent to the Thad Cochran Marine Aquaculture Center at the University of Southern Mississippi (USM) in Ocean Springs, MS. The USM facility was chosen because they operate a fully closed, recirculating aquaculture system (RAS) for oysters, and is therefore a de facto bio secure facility eliminating any risk of transfer of pathogens to Gulf waters during this project. The pediveliger larvae were set at USM, raised for a few weeks in their system, and a sample of these post-set seed were returned to VIMS SPL for disease analysis again. Each cohort was tested leaving the hatchery and returning after settlement. Pathology reports for all groups were negative. The significance of the negative reports on returning seed was that larvae contained no cryptic infections when they left OSH. 

Gulf Seed Transfers Under the Microscope: OSH 2024 Study

In 2024, our team received funding through The Nature Conservancy Supporting Oyster Aquaculture and Restoration (SOAR) program to examine the biosecurity of post-set oyster seed to the Gulf of Mexico. Spawns for this project, just like our 2023 biosecurity project, utilized broodstock from Gulf and Virginia origins. The objective of using the Virginia broodstock was to demonstrate that parent oysters residing in Virginia waters—where diseases of concern are endemic—would not transmit those diseases to post-set seed. For the SOAR project, 5 cohorts were spawned and reared to post-set. Most cohorts were tested as 1, 4, and 7 day old seed at VIMS SPL and subsequently shipped to USM. The other cohorts were tested at 4 or 11 days old. After three weeks of growing in the quarantine system at USM, each cohort was shipped back to VIMS SPL for a second round of pathology testing. 

No pathogens were detected in any group leaving the OSH hatchery, nor any group returning from their culture period at USM. As with our larvae study in 2023, the extra step of holding cultures at USM was meant to demonstrate that there was no incipient pathology or hitchhiking pathogens at the time of transfer from our hatchery that could manifest as an infection later during nursery culture. Pathogen screening methods included highly sensitive PCR techniques (a total of 75), in addition to traditional stained-slide microscopy.

Looking Ahead 

Our 2023 and 2024 projects provide evidence that RSSBP-guided biosecurity practices support the safe transfer of post-set oyster seed from the Atlantic to the Gulf. By using broodstock from Virginia sources, we were able to demonstrate the lack of pathogen transfer from adult to larva. Across multiple cohorts, rigorous testing of seed from both the OSH hatchery and the USM quarantine facility showed no signs of pathogens, even after an extended post transfer culture period. Continued research and adherence to these biosecurity measures are key to providing evidence-based biosecurity protocols for decision makers in the Gulf. Approval of such transfers could help stabilize Gulf oyster culture and catalyze its growth.