Seasonal filtering of nitrogen-fixing microbial communities in a temperate estuary
MS in Marine Biology Thesis Defense by Emma Steedman
Committee Members
Dr. Pia Moisander
Professor, Department of Biology
Thesis Advisor
Dr. Jefferson Turner
Chancellor Professor, Department of Biology
Thesis Committee
Dr. Christian Petitpas
Shellfish Program Leader, Massachusetts Division of Marine Fisheries
Thesis Committee
Abstract:
Nitrogen-fixing microbes (diazotrophs)—support productivity in marine ecosystems but their dynamics in temperate coastal waters remain poorly characterised. Using monthly nifH amplicon sequencing and environmental data collected over nine years (2011-2020) in Buzzards Bay, diazotroph diversity and community composition were assessed in the context of environmental drivers.
Diazotroph Alpha diversity had limited seasonal variation in Richness but Shannon diversity and Evenness were higher in winter compared to summer. Community composition displayed clear seasonal variation, with winter and summer communities most distinct. Non-cyanobacterial diazotrophs were consistently prominent and exhibited marked seasonal shifts, with sulphate reducing taxa dominating. The cyanobacterial, algal symbiont UCYN-A (Candidatus Atelocyanobacterium thalassa) peaked consistently in late summer–early autumn, and was overwhelmingly dominated by clade A2, with minor contributions from clades A1 and A4.
Temperature (°C) was the primary factor correlating with community composition, with turbidity, salinity, and nutrients also contributing. Diazotroph dynamics were broadly similar between the coastal and mid-bay stations; however, significantly higher Richness at the coastal station compared to mid-bay indicates nearshore or sedimentary influence playing a role in diazotroph community assembly. Overall, seasonal environmental filtering shapes diazotroph community structure in this temperate estuarine system, with niche differentiation among dominant taxa underpinning the temporal stability of the potential for nitrogen-fixation capacity.
Zoom link:
https://umassd.zoom.us/j/94125276460
Zoom ID and password required.
Email Marlene Roberge to obtain password: mroberge1@umassd.edu.
Virtual
Pia Moisander
508-999-8222
pmoisander@umassd.edu
https://umassd.zoom.us/j/94125276460