Diatoms - My Way into Science

by Xavier Benito

**Spoiler: While I personally have tons of admiration to those who leave academia after Master/PhD graduation, this post is dedicated to those early-career researchers who stay and continue along the bittersweet journey called academia **

Fig.1: Achnanthes submarina Hustedt, a dominant diatom 
species of the Ebro Delta habitats. Photo by X. Benito

To begin with, I could write about how today's early-career researchers' personal and professional lives are stressful. Instead, I will write about how important passion and curiousness about nature are in finding your way into science. Personally, I am fascinated by diatoms (Fig. 1), a group of siliceous glass-encased algae, because they can be used to understand past and present environmental conditions in nearly all aquatic ecosystems. Thus, during my PhD in Spain, I studied diatoms found in Mediterranean deltaic ecosystems by applying GIS, ecology and palaeoecology approaches. For example, in the Ebro Delta, I found a high diversity of diatoms (407 taxa to be exact) from only 24 samples! These results inspired me to continue studying diatom flora in other regions. Upon completing my PhD, I was fortunate enough to start my first postdoctoral position studying the biogeography of tropical South American diatoms at the University of Nebraska-Lincoln (UNL); the Nebraskan landscape, while homogeneously beautiful, cannot be compared with Andean and Amazonian freshwater biodiversity. 

South American diatom biodiversity

The biodiversity of the South American continent was crucial for Charles Darwin's Origin of Species seminal theory that populations evolve over the course of generations through a process of natural selection. During his travel, Darwin recognized the importance of biogeography and history and how these two factors work together to shape life on Earth. While in South America, Darwin learned about Professor Christian Ehrenberg's microscopic observations of diatoms. Due to the old age of these diatom-rich geological deposits called diatomites, based on his new theory, Darwin thought that the diatoms should be old and have a wide geographical distribution. Maybe without directly saying it, the first observations of South American diatoms by Darwin and Ehrenberg back in the 19th century, were strongly related to historical biogeography, which is nowadays a hot topic in microbial biogeography discussions. That is, due to the massive dispersal capacity and large populations of microorganisms, including diatoms, cosmopolitan (existing worldwide) distribution patterns should prevail over restricted, endemic (typical for one region) distribution patterns. In other words, everything is everywhere and the environment makes the selection, also known as the Baas-Becking hypothesis [1]. This framework was the core motivation of my next research, which built upon questions of diatom dispersal and long-term and regional perspectives of environmental change.

Fig. 2: Lake Chiriacu, Ecuadorean Andes. Photo by X. Benito

In the tropical Andes, some authors have challenged the view that diatoms are cosmopolitan, arguing that a higher number of endemisms should exist than those currently known [2]. One of the most comprehensive diatom floras identified 888 diatom taxa from 350 samples randomly distributed from Venezuela to Argentina along the Andes [3], while another study found 228 taxa in a single sample from an Andean Bolivian stream (with many taxa not identified at the species level) [2]. Furthermore, by analyzing a diatom metadatabase from the tropical Andes and adjacent lowlands, my colleagues and I found a total of 1,086 taxa in 163 aquatic samples, including streams and lakes, and estimated the joint contribution of local environmental variables (water chemistry) and dispersal dynamics (spatial factors such as aquatic connectivity) in affecting diatom community composition [4]. These recent studies show how biologically diverse and complex Andean aquatic environments are, and how a great portion of the diatom flora seems yet to be discovered.

My take on diatom diversity

Because diatoms are one of the most important components at the base of the food chain in aquatic environments, I was curious whether diatoms could be used to investigate potential human-environment impacts. I recognize that ecological problems are also social problems. For instance, human-induced climate change threatens to jeopardize many of the world's ecosystems services (benefits that nature provides to human societies such as water provision from lakes, agricultural resources from land, or coastal protection from storms). In my current postdoctoral fellowship at the National Socio-Environmental Synthesis Center (SESYNC), I study coupled long-term human-environment systems using tropical Andean lakes as model systems. Despite the apparent pristine conditions of Andean lakes (Fig. 2), humans have shaped a dynamic cultural landscape following the Inca empire expansion (AD 1450) and Spanish colonization (AD 1542). Currently, population growth and poverty as well as damming, cattle grazing and fish stocking threaten lake and páramo grassland ecosystems that in turn provide water resources to rural and urban communities. However, understanding such complex socio-ecological systems in the high-altitude tropical Andes is challenging due to the lack of long-term consistent data sets. This knowledge gap may be limiting our understanding of the impending impacts of human-induced climate change in mountain communities [5].

Ongoing work & outlook

Diatoms have been always at the core of my research and inspiration to continuously seek new approaches and ideas that will ultimately help people and nature. With a group of colleagues and collaborators, I am analyzing a unique combination of diatom community data, biophysical data (pollen and sediment geochemistry), and human data (archaeological records) to understand the nature and trajectories of human-environment couplings in the tropical Andes over time. Our preliminary results demonstrate a concomitant change occurred approximately 2000 years ago in three different Andean lakes of varied size and chemistries, which may allow asking whether early-warning signals precede these synchronous transitions.
Studies that address questions on adaptive dynamics, resilience for people and ecosystems may be more useful than studies using static, neo-ecological approaches (e.g. short-term studies) [6]. Thus, I will investigate how historical and palaeoecological perspectives of resilience can provide an alternative understanding to the monitoring-oriented approach in these socio-economic valuable ecosystems, which provide multiple goods for much of Andean and Amazonian nations.


by Xavier Benito, PhD
Postdoctoral fellow at the National Socio-Environment Synthesis Center (SESYNC)


If you have questions or comments concerning Xavier's post, please leave a comment below. You can also visit his website or connect with him on Twitter. 

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References:

[1] Williams, D.M. (2011) Historical biogeography, microbial endemism and the role of classification: everything is endemic. In Fontaneto, D. (ed) Biogeography of Microscopic Organisms. Is Everything Small Everywhere? Cambridge University Press, Cambridge.
[2] Morales, E.A., Novais, M.H., Chávez, G., Hoffmann, L. & Ector, L. (2012) Diatoms (Bacillariophyceae) from the Bolivian Altiplano: Three new araphid species from the Desaguadero River draining Lake Titicaca. Fottea, 12, 41–58.
[3] Rumrich, U., Lange-Bertalot, H. & Rumrich, M. (2000) Diatoms of the Andes, from Venezuela to Patagonia/Tierra Del Fuego, and Two Additional Contributions. Iconographia diatomologica 9 ARG Gartner Verlag KG, Königstein.
[4] Benito, X., Fritz, S.C., Steinitz-Kannan, M., Tapia, P., Kelly, M.A. & Lowell, T.V. (2018) Geo-climatic factors drive diatom community distribution in tropical South American freshwaters. Journal of Ecology, 106, 1660–1672
[5] Wymann von Dach, S., Bracher, C., Peralvo, M., Perez, K., Adler, C., et al. 2018. Leaving no one in mountains behind: Localizing the SDGs for resilience of mountain people and ecosystems. Issue Brief on Sustainable Mountain Development. Bern, Switzerland: Centre for Development and Environment and Mountain Research Initiative, with Bern Open Publishing (BOP).
[6] Knapp, Gregory. 1991. Andean Ecology: Adaptive Dynamics in Ecuador. Westview Press