Geography and Environment Prospective Students

Phytoplankton play a key role in removing carbon dioxide from the air, what makes them thrive?
Numerical and Statistical Characterization of Phytoplankton Niches

Marine photosynthetic organisms known as phytoplankton are responsible for approximately 50% of the photosynthesis that takes place on earth and play a critical role in the planet's carbon cycle. Thus, with the surge in carbon dioxide released into the atmosphere over the past century, it has become increasingly important to understand the biological and chemical conditions which are most conducive the survival of such a ubiquitous and essential marine organism. The focus of this study is to define these conditions for approximately twenty different species of phytoplankton and ultimately, develop a statistical model for their distribution throughout the North Atlantic. In doing so, I hope to elucidate both the environmental conditions these species prefer as well as the associations various species have with one another.

At present , I am exploring two different statistical techniques for the model. The first, known as a Generalized Additive Model, fits smooth curves to the various environmental parameters and combines these covariates into a multiple additive regression. The second technique, known as Maxent, restricts the distribution based on certain observed conditions and fits the model which adheres to these conditions and at the same time, remains as close to the uniform distribution (also known as the distribution with the “maximum entropy”) as possible.

My supervisor for this project is Dr. Andrew Irwin and my research is supported by an NSERC Undergraduate Summer Research Award.

Has climate change influenced the morphological evolution of silicoflagellates over the last 65 million years?

Helena van Tol

Over the past 65 million years, diatoms and dinoflagellates have decreased in size. These are photosynthetic marine plankton which form biogenic opaline silica cases (like glass). It is thought that evolution towards smaller cell sizes for these siliceous phytoplankton may be a response to the shift from an ancient “greenhouse” to the more recent “icehouse” climate. As the oceans became less well-mixed, less nutrients became available in the upper layer where sunlight penetrates. Therefore, species of siliceous phytoplankton which use less silica to build their skeletons are more likely to outperform larger cells which require more nutrients.

This theory is of some relevance to the construction of current climate models. Phytoplankton, particularly heavy siliceous ones such as diatoms, capture a massive quantity of carbon from the Earth’s atmosphere. Some portion of this carbon will be transferred back up the food web and some will sink to the deep ocean in a process known as the biological pump. The smaller cells, seen today, would have a lower sinking rate than those in the past and store less carbon in the ocean depths.

I am creating a database of first and last appearances of silicoflagellate species in the fossil record and collecting a variety of morphological metrics from images in the literature. By graphing species diversity and changes in these features through geologic time it’s possible to identify mass extinctions, determine the effects of mass extinctions on silicoflagellate evolution, and perhaps observe a general change in morphology over time.

My supervisor for this project is Dr. Zoe Finkel and I am able to spend the summer doing this work thanks to receiving an NSERC Undergraduate Summer Research Award.

The world's oceans are a significant source of primary productivity, with photosynthetic singled-celled organisms such as cyanobacteria and diatoms forming the basis of the food web. Understanding the population structure of the phytoplankton community is very important for understanding the ecology of the oceans, which has a global impact on climate. One important factor in determining which organisms fill specific niches is size, which varies with both genome size and metabolic rates.

Cells with higher metabolic rates growth faster, meaning they tend to dominate the phytoplankton population, at least in terms of numbers. In general, for all organisms, metabolic rate relative to mass is lower in larger cells. This means that smaller cells should dominate populations of phytoplankton. As larger cells are fairly common, there are other advantages to being large, including escaping predation and different responses to light.

Another big correlation present in Eukaryotes is that cell size is correlated to genome size. This is interesting because most of eukaryotic DNA is non- coding, that is it's not a gene, and doesn't get transcribed. A possible function for this seemingly useless DNA would be that it is necessary to support larger cells. Cell size is largely determined by the regulation of the cell cycle, which is related back to metabolic rates.

My research uses the diatom Ditylum brightwelli to examine these relationships within a single species. As diatoms grow and divide constraints in their rigid silica shell cause decreases in width. In addition to looking at this variation of size over the life cycle of Ditylum brightwelli, I use two different populations of the diatom, one with a genome twice the size and correspondingly larger cells. By comparing the growth rates and sizes of the different populations I can see how either genome size or cell size control metabolic rate. A better understanding of what fundamentally determines the growth rates of phytoplankton could yield insights into why certain sizes of phytoplankton are suited to certain environmental conditions.

I'm supervised by Drs. Zoe Finkel and Dr. Amanda Cockshutt. This is my second summer working on the project. Last summer I was funded by an NSERC Undergraduate Student Research Award and this summer I'm funded by a RTM Allan Summer Research Fellowship. I also completed an independent study credit last fall for work on this project.