Electronic Thesis and Dissertation Repository

Thesis Format



Master of Science




Tai, Vera


Understanding zooplankton productivity is critical for modeling marine food web function, of which one poorly known factor is the influence of zooplankton symbionts. Zooplankton protist symbiont diversity is underestimated due to the limited surveys and techniques previously used. Using 18S V4 metabarcoding, I characterized the eukaryotic microbiomes associated with crustacean zooplankton from the northern Strait of Georgia, BC. Apostome ciliates were most abundant in all hosts except for cyclopoid copepods, which were dominated by Syndiniales. Most symbiont lineages were more abundant in one or two hosts, suggesting some degree of host preference. Microbiome data also provided information on diet, confirming increased diatom consumption during spring in calanoid copepods and consumption of crustaceans by Cyphocaris and Corycaeus. These data also suggest that zooplankton feed on siphonophores, a previously unrecognized interaction with the Cnidaria. My work contributes to resolving the interactions between zooplankton and alveolate symbionts, and the host-specificity of potential parasites.

Summary for Lay Audience

Marine zooplankton are small animals and microorganisms that live in the ocean and eat other organisms. Animal zooplankton include well known groups such as copepods, krill, jellyfish, the larval stages of fish, crabs, lobsters, and shrimp, and many more. Zooplankton are crucial components of the marine food web because many of them feed on photosynthetic microorganisms called phytoplankton (including cyanobacteria, diatoms, and dinoflagellates) at the base of the food web. Zooplankton are themselves consumed, which transfers energy up the food web to support the growth of fish, whales, and birds at the highest trophic levels. It is important to understand how the growth of zooplankton is influenced by their environment, including their interactions with other organisms, due to their importance in food web stability. One interaction that is often overlooked or less understood is that between zooplankton and their microbial symbionts. Symbionts of zooplankton may live attached to their surface or inside their body and can have a range of effects on their hosts, from beneficial to harmful, the latter referred to as parasitism. Symbiotic microorganisms have been observed in zooplankton since at least the early 1900’s, although the true diversity of these symbionts is not known for most zooplankton, let alone their effects on the host. Microscopy is inadequate to detect and identify these symbionts, whereas DNA sequences can be used instead to determine their presence in zooplankton. This thesis is one of the first studies to characterize the microbial symbionts associated with various species of marine zooplankton using DNA sequencing methods. Ciliate and dinoflagellate lineages were the most abundant symbionts associated with crustacean zooplankton, such as copepods. Most symbionts were found associated with almost every zooplankton host analyzed, but some degree of preference for particular hosts was observed. Sequence data also provided insight into potential components of zooplankton diet including herbivory of diatoms in spring, and carnivory of crustaceans and cnidarians – which has not been known before. The high diversity of symbionts associated with zooplankton, many of which were previously undescribed, indicates potentially important and unrecognized interactions in the marine food web.