Name: Joanne Salzer
Date: 07/29/2026
Time (EST/EDT): 10:00 am
Location: IMET Auditorium
Remote Access: email: mees@umd.edu

Committee Chair: Allen Place
Committee Members: Jonathan Deeds Tsvetan Bachvaroff

Title: Investigating the Role of Symbiotic Algae in Palytoxin Production by Aquarium-Sourced Zoanthids

Abstract: Palytoxin is one of the most potent non-protein marine toxins known and has been detected in aquarium-sourced zoanthids, posing a potential human health risk to aquarium hobbyists and others who handle these organisms. However, the biological origin of palytoxin in zoanthids remains unresolved. Proposed sources include the cnidarian host, Symbiodiniaceae algal symbionts, associated bacteria, or the holobiont collectively. Rather than framing palytoxin production as a simple host-versus-symbiont question, my thesis frames the system as a host-associated toxin phenotype that may depend on interactions among zoanthid genotype, dominant Symbiodiniaceae type, symbiont physiological state, and tissue-level storage dynamics. Palytoxin concentrations were quantified from both commercial aquarium store-sourced zoanthid colonies, as well as samples obtained directly from home aquarium poisoning events and paired with host and symbiont taxonomic assignments. To experimentally disrupt the host-symbiont association, toxic zoanthids sourced from a local aquarium store and maintained in the laboratory were subjected to (-)menthol bleaching treatments, and changes in pigmentation, symbiont cell density, tissue palytoxin concentration, and palytoxin concentration in the particulate fraction of release into incubation water were measured. Overall, palytoxin was detected in 50% of sampled colonies and varied widely among positive samples. Toxin presence was strongly associated with host clade, and symbiont genotypes were host-specific but alone did not explain toxin presence. In the bleaching experiment, (-)menthol reduced symbiont density and caused visible bleaching, but tissue palytoxin concentration in the zoanthid polyps did not decline over the experimental period (8 days). However, palytoxin was detected in incubation-water pellets from (-)menthol-treated samples and increased over time, while no palytoxin was detected in control incubation water pellets. Together, these results suggest that palytoxin production in aquarium-sourced zoanthids is strongly structured by host identity but may still involve Symbiodiniaceae-mediated or holobiont-level processes.