Caroline Link

Date of Award

2022

Document Type

Thesis

Degree Name

Bachelors

Department

Natural Sciences

First Advisor

Diaz Almeyda, Erika

Area of Concentration

Marine Biology

Abstract

The driving force between the high biodiversity and productivity of coral reefs is corals’ symbiotic relationship with photosynthetic dinoflagellates within the family Symbiodiniaceae. Recent studies have found that Symbiodiniaceae species differ in their physiological thermotolerances and that symbiont identity is a key determinant of a coral host’s susceptibility and acclimation to increased temperature. However, the specific thermotolerances between species and among species strains remain partially unknown. This is due in part to the difficulty associated with maintaining ex hospite symbionts in culture and sourcing intact coral-algal holobionts with a symbiont that has known physiology when in culture. Cassiopea xamachana jellyfish, which are easily sourced, cultured, and infected with a range of Symbiodinaceae strains, is a potential model organism for coral-algal symbioses. Here we compared the thermotolerance of Symbiodinium tridacnidorum (strain CassEL-1) when in culture versus in hospite within C. xamachana ephyrae. S. tridacnidorum cultures were found to be thermosensitive. Meanwhile, in hospite symbionts displayed significantly increased thermotolerance at the onset of treatment, which began to fade after 6 days at 32°C. This suggests that Cassiopea may provide symbionts with some degree of protection during initial stress exposure. Furthermore, host age, size, and health were found to not significantly affect symbiont photosynthetic efficiency and thermotolerance. Taken together, these results highlight the need for further study on host-symbiont interactions under environmental stress and provide valuable considerations for the future use of C. xamachana as a model organism.

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