Date of Award
2026
Degree Type
Dissertation
Degree Name
Doctor of Philosophy in Biological and Environmental Sciences
Department
Biological Sciences
First Advisor
Marta Gomez-Chiarri
Abstract
Bivalve molluscs are ecologically and economically important species in aquaculture, yet their production is threatened by multiple disease-related challenges, including bacterial larval crashes in hatcheries and disseminated neoplasia in farmed populations of hard clams Mercenaria mercenaria. This dissertation addressed these two distinct areas of bivalve health research through the development of new tools for pathogen screening, disease mitigation, and molecular diagnosis.
The first part of this dissertation focused on bacterial pathogens associated with larval crashes in bivalve hatcheries. A rapid hemocyte-based viability assay was developed and optimized to evaluate bacterial virulence using adult oyster hemocytes. This assay correlated well with traditional larval challenge assays, supporting its use as a practical and efficient alternative for screening potentially pathogenic bacteria. Application of this assay to hatchery-associated isolates identified multiple bacterial strains with pathogenic potential, while also indicating that larval crashes are not caused by a single bacterial species or taxonomic group. Selected pathogenic strains were characterized through whole genome assembly and annotation.
The second component of this work focused on the identification and development of probiotic bacteria capable of improving larval resilience. Bacterial isolates recovered from bivalves were screened for multiple probiotic-associated traits, including antimicrobial activity, quorum-quenching ability, biofilm formation, and compatibility with other beneficial strains. Four promising candidates, Algoriphagus yeomjeoni DEN5, Glutamicibacter soli CLAM16, Pseudooceanicola nitratireducens NEH7, and Marinomonas gallaica CLAM9, were selected for further evaluation. These isolates were safe for larvae and improved survival during pathogen challenge. Multi-strain probiotic formulations provided even greater protection, outperforming the established probiont Phaeobacter inhibens S4 alone and increasing larval survival against a broad range of pathogens isolated from hatchery crashes.
The final part of this dissertation examined disseminated neoplasia in the hard clam, Mercenaria mercenaria, using single-cell RNA sequencing. Cohabitation experiments confirmed disease transmission, and transcriptomic analysis revealed nine distinct hemocyte populations, including a cluster composed predominantly of neoplastic cells. This neoplastic population exhibited transcriptional signatures consistent with immune evasion, resistance to apoptosis, altered signaling, and metabolic reprogramming. Copy number variation analysis further revealed substantial genomic instability in neoplastic hemocytes. In addition, two neoplasia-specific genes, LOC123550102 and LOC128554517, were identified as promising diagnostic markers for disseminated neoplasia.
Together, these studies advance the understanding of bivalve disease by providing a rapid assay for bacterial virulence screening, a multi-strain probiotic strategy for improving larval survival, and new molecular insight into disseminated neoplasia in hard clams. These findings contribute practical and mechanistic tools for improving disease management and health assessment in bivalves.
Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.
Recommended Citation
Samson, Jaypee Solsana, "INVESTIGATING THE ETIOLOGIES OF BIVALVE HEALTH CHALLENGES: LARVAL CRASHES, DISSEMINATED NEOPLASIA, AND STRATEGIES FOR ENHANCING RESILIENCE AND DIAGNOSTIC APPROACHES" (2026). Open Access Dissertations. Paper 4563.
https://digitalcommons.uri.edu/oa_diss/4563