Tracing Molecules Through Oligotrophic Marine Ecosystems: Microbial Hydrocarbon Cycling and Coral Trophic Ecology

• Main Author: Love, Connor
• Other Authors: Valentine, David L
• Format: Thesis
• Language: English
• Published: eScholarship, University of California 2023
• Subjects: Biological oceanography; Geochemistry; Environmental science; biology; chemistry; climate; coral; cyanobacteria; ocean; North Atlantic
• Online Access: https://escholarship.org/uc/item/7b03n1s7

The creation, movement, and consumption of distinct biomolecules by marine organisms has far reaching implications regarding ecosystem material and energy flow and how we manage the marine environment. Lipids are ubiquitous, energy rich biomolecules that are essential for all life and are used for cell membrane structure, energy storage and serve as useful indicators for ecosystem and food web dynamics. In this dissertation, the flow of specific lipid biomolecules through multiple marine environments is measured, explored, and clarified to better understand biogeochemical cycles, marine food webs and ecosystem connectivity. In the first chapter of my dissertation, I measure, quantify, and close the loop of the open ocean microbial hydrocarbon cycle, with implications for priming effects of the ocean microbiome to oil spills. It is estimated that seeps, spills, and other oil pollution introduce ~ 1.3 million tons (1.3 Tg) of hydrocarbons into the ocean each year. Additionally, it is known that globally abundant marine cyanobacteria Prochlorococcus and Synechococcus which account for ~25% of ocean net primary production also produce hydrocarbons from fatty acids. But little is known about the size, turnover and fate of these cyanobacterial hydrocarbons and the implications for the ocean’s microbiome response to future oil spills. From a research expedition in the North Atlantic, I report that cyanobacteria in an oligotrophic gyre mainly produce n-pentadecane which correlates tightly with fluorescence and Prochlorococcus abundance in oligotrophic waters. Using chemical and isotopic tracing I find that pentadecane production and diel dynamics mainly occurs in the lower euphotic zone at the deep chlorophyll maximum. I estimate the global flux of cyanobacteria-produced pentadecane exceeds total oil input in the ocean by 100 to 500-fold, with cyanobacteria producing ~ 130-650 million tons of pentadecane per year. Analysis of sinking particles at the base of the euphotic zone show that nearly all pentadecane (< 0.001 ...