Symbiont diversity in the eukaryotic microbiomes of marine crustacean zooplankton.

This article focuses on characterizing the diversity, host specificity, and ecological roles of protist symbionts associated with dominant crustacean zooplankton taxa—copepods, euphausiids, amphipods, and ostracods—in the northern Strait of Georgia, Canada, using DNA metabarcoding of the V4 region of the 18S rRNA gene. The study found that alveolate protists, particularly apostome ciliates and Syndiniales dinoflagellates, dominate zooplankton microbiomes, with many symbionts showing host preferences but also broad host ranges. Several identified symbionts belong to known parasitic lineages that may significantly affect zooplankton productivity and mortality, while others represent potentially novel species. Additionally, free-living protists such as diatoms and hydrozoans were detected and inferred to be part of zooplankton diets, suggesting an underappreciated pathway for carbon cycling. The findings highlight the complexity and ecological significance of protist-zooplankton symbioses and underscore the need for further research on their life cycles, transmission, and impacts on marine food webs.