Jellyfish blooms Through the Microbial Lens: Temporal Changes, Cross-Species and Jellyfish-Water Comparisons

Abstract

In this study, we explore the dynamics of bacterial communities associated withRhopilema nomadicablooms, the predominant jellyfish in the Eastern Mediterranean Sea. We collected over 120 samples from more than 30 individuals across five major bloom events, capturing both lesser-studied winter blooms and the peaks and declines of summer blooms. Our analysis revealed significant microbial shifts-increases inEndozoicomonasand unclassifiedRickettsialeswere significantly more abundance during late summer blooms, whileTenacibaculumdominated in winter. Additionally, we examined microbial patterns within specific tissues—bell, gonads, tentacles, and gastrovascular system—to assess variations across these different niches. This revealed high relative abundance of specific taxa tailored to different tissue-Bacteroideswas predominantly found in the bell,Simkaniaceaein the gonads, andEndozoicomonasin the tentacles. Further expanding our research, we compared the top taxa ofR. nomadicawith those of nine other jellyfish species from different locations. Interestingly, while no universal core microbiome was found, several taxa, includingEndozoicomonas,Mycoplasma, andSpiroplasma, were common across different species, suggesting their potential ecological roles across jellyfish. Lastly, our study of potential bacterial transmission modes revealed that key bacteria associated withR. nomadicaare exclusively found near bloom areas, and are absent from remote seawater, highlighting potential localized transmission dynamics between jellyfish and their immediate marine environment. Our study marks the first exploration of microbial dynamics withinR. nomadica, while also broadening the understanding of other jellyfish microbial communities and setting the stage for future studies to delve deeper into their complex interactions.