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 with Rhopilema nomadica blooms, 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 in Endozoicomonas and unclassified Rickettsiales were significantly more abundance during late summer blooms, while Tenacibaculum dominated 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-Bacteroides was predominantly found in the bell, Simkaniaceae in the gonads, and Endozoicomonas in the tentacles. Further expanding our research, we compared the top taxa of R. nomadica with those of nine other jellyfish species from different locations. Interestingly, while no universal core microbiome was found, several taxa, including Endozoicomonas, Mycoplasma, and Spiroplasma, 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 with R. nomadica are 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 within R. 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. IMPORTANCEJellyfish blooms, like those of Rhopilema nomadica in the Eastern Mediterranean, impact marine ecosystems and human industries. Understanding the complex relationships between jellyfish and their microbiomes is important, as these interactions may influence bloom formation and decline. Our study explores microbiome variations across different stages of R. nomadica blooms, identifies common bacteria among jellyfish from various locations, and examines potential transmission modes of the main jellyfish-associated bacteria. Microbial communities vary significantly between bloom stages and jellyfish tissues, becoming less diverse towards the end of the bloom. Although no universal core microbiome was discovered, taxa such as Endozoicomonas, Mycoplasma, and Spiroplasma are prevalent across various jellyfish, suggesting significant ecological roles. Finally, our findings indicate that key bacteria associated with R. nomadica predominantly reside near bloom areas and are absent from distant seawater, highlighting localized transmission mode. This study enhances our understanding of jellyfish-associated microbial communities and their role in bloom dynamics.