Bachand, PaxtonPowers, NicoleHaye, Kenneth C.Pinnell, LeeTominack, SarahTurner, JeffreyWetz, Michael S.2022-07-012022-07-012022-04https://hdl.handle.net/1969.6/92586Aureoumbra lagunensis forms persistent brown tide algal blooms that disrupt ecosystem processes through light attenuation, decreased oxygen availability, and reduced sediment stabilization. These disruptions have negative, cascading effects on the ecology and economy of coastal regions. Nearly four decades of research has explored the environmental and anthropogenic drivers of A. lagunensis blooms, yet previous research has not explored a bloom’s microbiome. Here, we present a holistic study wherein we characterized the water quality parameters and microbial consortia associated with a recurrent brown tide bloom, utilizing nearby non-bloom waters as comparison. Bloom waters were characterized by higher oxygen, pH, salinity, water temperature, chlorophyll a, and organic nitrogen and carbon concentrations. Variation in algal cell con- centrations were explained largely through dissolved organic nitrogen, organic carbon, and oxygen. Several bacterial taxa were significantly more abundant in bloom samples: Alphaproteobacteria (Rhodobacterales; 8.41%), Gammaproteobacteria (Chromatiaceae; 2.11% & Alcanivoracaceaewere; 1.73%), and Cyanobacte- ria (Nostocales; 4.50%). Alphaproteobacteria and Gammaproteobacteria have the potential to mediate B-vitamin acquisition and supply of sulfur compounds, respectively, in addition to the supply of reduced carbon and nitrogen compounds through cyanobacterial bloom co-dominance. Additionally, conditionally rare taxa that comprised nearly 15% of the bloom community (𝑃 ℎ𝑦𝑐𝑖𝑠𝑝ℎ𝑎𝑒𝑟𝑎𝑒(2.02) may mediate organic compound degradation, vitamin acquisition, and algal pathogenesis. Collectively, these results confirm and expand understanding of bloom drivers and demonstrate that A. lagunensis blooms are colonized by a unique microbial consortium that likely plays a significant role in bloom dynamics. Although a small percentage of the bloom’s community, these low abundance organisms can contribute disproportionate effects to the ecosystem and therefore play an important role in regulating bloom dynamics.Attribution 4.0 Internationalhttp://creativecommons.org/licenses/by/4.0/microbial ecology16s rrnaharmful algae bloomeutrophicationPresentation