#EcosystemModel

[themetaphorical]

WAKE UP—THE LIGHTS HAVE CHANGED

A recent study has revealed that an ancient oceanic plate, once part of the Tethys Ocean, is currently tearing apart beneath Iraq and Iran. This geological activity is significantly influenced by the Zagros Mountains, which play a crucial role in the bending and deformation of Earth’s surface in this region. The Tethys Ocean existed during the time of the supercontinent Pangaea, and its remnants…

[bettreworld]

#1 From DNA to Satellite Imagery, Disciplines Merge to Create Better Eco...

[datasciencegirl]

Diversity is the Key to Phytoplankton Productivity

My submission to the PacX challenge discussed in my previous posts was motivated by the main thrust of my research: modeling phytoplankton diversity in the ocean.

Thousands of phytoplankton species live throughout the ocean. These microscopic, plant-like, single celled organisms differ in their preferences for nutrients, light, and temperature. Some can cope with very low nutrient concentrations in oceanic Gyres, while others cannot live without high pulses of nutrients and light. These differences allow phytoplankton species to fill various ecological niches and therefore avoid competition for resources.

Despite this large variety of phytoplankton species in the ocean, ecosystem modelers often only consider a handful of types - usually TWO, to be exact. Depending on the question at hand, including only one "big" and one "small" phytoplankton does the trick. But when questioning the functioning of an ecosystem with a variety of niches, it may be important to represent the diverse array of life in the ocean.

A novel approach to model phytoplankton diversity in the ocean has been developed by Mick Follows, Penny Chisholm and other members of The Darwin Project at MIT. This group has formulated a self-emergent ecosystem model that includes on the order of 100 phytoplankton types (78 to be exact). While not exactly representative of the large number of species in the ocean, these analogs for phytoplankton species this representation of modeled diversity comes closer than ever before. The variety of modeled phytoplankton types are "designed" by randomly assigning a set of traits that  enable survival in a range of realistic conditions (e.g., low or high nutrients, warm or cold water, high or low light). All of these phytoplankton types are "thrown" into a realistic physical and chemical simulated ocean, and the games begin - phytoplankton "emerge" in regions where they are suited to thrive. 

The Darwin Project group applies this modeling approach on a global scale, displaying enlightening insights into the factors that drive phytoplankton diversity patterns across the entire ocean, as shown in Andrew Barton's figure of global phytoplankton diversity above. At  the University of California Santa Cruz, Chris Edwards, John Zehr and myself applied this modeling approach on a local scale to the California Current System (CCS). As a result, the model performed well, capturing observations of silicate-imbibing diatoms in the high nutrient, chilly coastal waters as well as the small phytoplankton types able to withstand the low nutrient, relatively calm and warm waters offshore. The model also represented seasonal/temporal variation in the phytoplankton types, with large diatom blooms that coincided with the spring upwelling season, and an increase in small phytoplankton types in winter.

The ability of the model to capture these general temporal (seasonal) and spatial (biogeographies) variations provided confidence in the model performance. However, of the 78 phytoplankton types modeled, only a dozen or so contributed to the upper 99% of the total modeled phytoplankton biomass (or productivity). What about the remaining 65 phytoplankton types just hanging around at low, background concentrations? Would these types play an important role with changing environmental conditions?  Or were we "wasting" a bunch of computational effort to calculate the activity of 65 phytoplankton types that simply "hung around" in the background contributing very little? 

Ecological research questions aside, I was slightly fed-up with the time it took to run these computer-intensive model simulations (!). And I could not help but wonder, "How many phytoplankton do we actually need to model the CCS?". This led to a new application of this modeling approach that tested the link between phytoplankton diversity and their function in the ocean ecosystem.