Defining the ecological and physiological traits of phytoplankton across marine ecosystems
Defining the ecological and physiological traits of phytoplankton across marine ecosystems
Date
2016-02
Authors
Alexander, Harriet
Linked Authors
Person
Alternative Title
Citable URI
As Published
Date Created
Location
DOI
10.1575/1912/7755
Related Materials
Replaces
Replaced By
Keywords
Kilo Moana (Ship) Cruise KM12-19
Knorr (Ship : 1970-) Cruise KN12-17
Phytoplankton
Ecology
Knorr (Ship : 1970-) Cruise KN12-17
Phytoplankton
Ecology
Abstract
Marine phytoplankton are central players in the global carbon cycle, responsible for nearly
half of global primary production. The identification of the factors controlling phytoplankton
ecology, physiology, and, ultimately, bloom dynamics has been a central problem in the
field of biological oceanography for the past century. Molecular approaches enable the direct
examination of species-specific metabolic profiles in mixed, natural communities, a task
which was previously intractable. In this thesis, I developed and applied novel analytical
tools and bioinformatic pipelines to characterize the physiological response of phytoplankton
to their environment at various levels of taxonomic grouping. An in silico Bayesian
statistical approach was designed to identify stable reference genes from high-throughput
sequence data for use in RT-qPCR assays or metatranscriptome studies. Using a metatranscriptomic
approach, the role of resource partitioning in the coexistence of two closely
related diatom species in an estuarine system was examined. This study demonstrated that
co-occurring diatoms in a dynamic coastal system have apparent differences in their capacity
to use nitrogen and phosphorus, and that these differences may facilitate the diversity
of the phytoplankton. The second field study focused on the diatom, haptophyte, and dinoflagellate
functional groups, using simulated blooms to characterize the traits that govern
the magnitude and timing of phytoplankton blooms in the oligotrophic ocean. The results
indicated that blooms form when phytoplankton are released from limitation by resources
and that the mechanistic basis for the success of one functional group over another may be
driven by how efficiently the transcriptome is modulated following a nutrient pulse. The
final study looked at the sub-species level, examining the balance of phenotypic plasticity
and strain diversity in the success of the coccolithophore Emiliania huxleyi. Results indicated
strong control of nitrogen on the species complex and showed that nutrient resupply
shifted the strain composition as well as transcript abundance of key biogeochemical genes
involved in nutrient acquisition and the life stage of the population. Together, these studies
demonstrate the breadth of information that can be garnered through the integration of
molecular approaches with traditional biological oceanographic surveys, with each illuminating
fundamental questions around phytoplankton ecology and bloom formation.
Description
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2016
Embargo Date
Citation
Alexander, H. (2016). Defining the ecological and physiological traits of phytoplankton across marine ecosystems [Doctoral thesis, Massachusetts Institute of Technology and Woods Hole Oceanographic Institution]. Woods Hole Open Access Server. https://doi.org/10.1575/1912/7755