Ciliate micrograzer dynamics of the New England Shelf

Abstract

Protists play important roles in grazing and nutrient recycling, but quantifying these roles has been hindered by difficulties in collecting, culturing, and observing these often-delicate cells. During long-term deployments at the Martha's Vineyard Coastal Observatory (MVCO) (Massachusetts, USA), Imaging FlowCytobot (IFCB) made it possible to study live cells in situ without the need to culture or preserve. IFCB records images of cells with chlorophyll fluorescence above a trigger threshold, so taxonomically resolved analysis of protists is limited to mixotrophs and herbivores, which have eaten recently. To overcome this limitation, I coupled a broad-application 'live cell' fluorescent stain with a modified IFCB so that protists which do not contain chlorophyll (such as consumers of unpigmented bacteria and other heterotrophs) can also be recorded. Staining IFCB (IFCB-S) revealed higher abundances of grazers than the original IFCB, as well as some cell types not previously detected. To analyze a 10-year time series of herbivorous ciliates at MVCO and address broad patterns of seasonality of major ciliate classes and their components, I employed a statistical model that estimates a seasonal density pattern and simultaneously accounts for and separates any annual-scale effects. I describe the seasonality of three functional groups: a phototrophic ciliate, a mixotroph, and a group of strict heterotrophs, and comment on potential drivers of these patterns. DNA sequencing has also contributed to the study of protist communities, providing new insight into diversity, predator-prey interactions, and discrepancies between morphologically defined species and genotype. To explore how well IFCB images can be used to detect seasonal community change of the class Spirotrichea, an important and numerous group, I used high-throughput sequencing (HTS), which does not discriminate between chlorophyll-containing cells and the rest of the community. I report on species and genera of ciliates for which morphotype and genotype displayed high congruency. In comparing how well temporal aspects of genotypes and morphotypes correspond, I found that HTS was critical to detect and identify certain ciliates occupying a niche associated with warmer temperatures. I further showed that when these types of analyses are combined with IFCB results, they can provide hypotheses about food preferences. These last six and a half years have been full of scientific and self-discovery. I could not have pursued this adventure without a village of support. I'd like to thank all of these people.To my advisor, Heidi, your guidance, patience, and belief in me is something I will always cherish and never forget. Apart from being an amazing advisor in a academic way (opening my eyes to diverse questions, guiding my writing, etc.), you also helped me with many life obstacles and stimulated me during my difficult moments. I am forever grateful I had you as role model throughout these years and for that I am a better scientist.To Rob, thank you for takin...

The genetic diversity of plastids associated with mixotrophic oligotrich ciliates

“…One of the most conspicuous plastidic oligotrichs is L. strobila , due to its widespread occurrence in temperate coastal ecosystems, large size, unique morphology, and cytoplasm densely packed with plastids (McManus and Fuhrman ; Montagnes et al ; Stoecker et al ; Agatha et al ). L. strobila is the most abundant mixotrophic oligotrich enumerated at MVCO by the in situ IFCB and peaks in April and May, representing ~ 14% of annual ciliate biomass (Brownlee ). In field populations, L. strobila has been shown to account for 8% of total phytoplankton primary production, and ~ 90% of microplankton primary production on the Georges Banks during early summer (Stoecker et al ).…”