Publication Date:
2022-05-25
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 September 2014
Description:
Synechococcus is a ubiquitous marine primary producer. Our understanding of the
factors that determine its abundance has been limited by available observational tools,
which have not been able to resolve population dynamics at timescales that match
response times of cells (hours-days). Development of an automated flow cytometer
(FlowCytobot) has enabled hourly observation of Synechococcus at the Martha’s
Vineyard Coastal Observatory (MVCO) since 2003. In order to ascribe changes in cell
abundances to either growth or loss processes, information on division rate is needed.
I refined a matrix population model that relates diel changes in the distribution of cell
volume to division rate and demonstrated that it provides accurate estimates of daily
division rate for both cultured and natural populations. Application of the model to
the 11-year MVCO time series reveals that division rate is temperature limited during
winter and spring, but light limited during fall. Inferred loss rates closely follow division
rate in magnitude over the entire seasonal cycle, suggesting that losses are mainly
generated by biological processes. While Synechococcus cell abundance, division rate,
and loss rate demonstrate striking seasonal patterns, there are also significant shorter
timescale variations and important multi-year trends that may be linked to climate.
Interpretation of population dynamic patterns is complicated by the diversity found
within marine Synechococcus, which is partitioned into 20 genetically distinct clades.
Each clade may represent an ecotype, with a distinct ecological niche. To understand
how diversity may affect population dynamics, I assessed the diversity at MVCO over
annual cycles with culture-independent and dependent approaches. The population
at MVCO is diverse, but dominated by clade I representatives throughout the year.
Other clades were only found during summer and fall. High through-put sequencing of
a diversity marker allowed a more quantitative investigation into these patterns. Five
main Synechococcus oligotypes that comprise the population showed seasonal abundance
patterns: peaking either during the spring bloom or during late summer and
fall. This pattern strongly suggests that features of seasonal abundance are affected
by the underlying diversity structure. Synechococcus abundance patterns result from
a complex interplay among seasonal environmental changes, diversity, and biological
losses.
Description:
This work was supported by a Department of Defense National Defense Science
and Engineering Graduate Fellowship, National Science Foundation Grants (OCE-
0530830 to M.G. Neubert, H.M. Sosik, R.J. Olson, and A.R. Solow, OCE-1031256 to
H.M. Sosik, DEB-1257545 to M.N. Neubert, and OCE-1155566 to A.F. Post), Gordon
and Betty Moore Foundation Grant 934 to H.M. Sosik, NASA Ocean Biology and
Biogeochemistry Program Grants NNX11AF07G and NNX13AC98G to H.M. Sosik,
student awards from the WHOI Ocean Ventures Fund and WHOI Coastal Ocean
Institute, and private donation.
Keywords:
Primary productivity
;
Biodiversity
;
Measurement
Repository Name:
Woods Hole Open Access Server
Type:
Thesis
Format:
application/pdf
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