Andrew Barton, together with Zoe Finkel (Mt Allison University, Sackville, New Brunswick, Canada), Ben Ward and Mick Follows have been examining the long-term Continuous Plankton Recorder (CPR) database on the abundances of diatom and dinoflagellate taxa in the North Atlantic Ocean
A marine ecosystem model that when initialized with many phytoplankton types whose physiological traits were determined stochastically, community structure and biogeography emerged to be consistent with known distributions of microbes in the global oceans.
Our numerical simulations show an equator-to-pole decrease in the diversity of phytoplankton species. Super-imposed on this gradient in the simulation are regions of high phytoplankton diversity which occur in association with areas of energetic flow including western boundary currents.
We are currently developing a “Quota” model which includes internal cellular processes such as photosynthesis, respiration and nutrient storage (the quota). This approach provides a more detailed representation of plankton physiology, and allows us to focus on some potentially important mechanisms in plankton ecology.
In region of low seasonality, resource competition theory (Tilman, Ecology, 58, 338, 1977; Tilman, Monographs in Population Biology, 17, 1982) is capable of predicting not only the competitive outcome amongst organisms in our model, but also the ecosystems control on the nutrient concentrations.
We are using our model to examine the development of biogeographical provinces in the model ocean. The simulations show clear and plausible organization of the emergent community structure by the physical regime: Strongly seasonal, high nutrient regimes are dominated by fast-growing bloom specialists, while stable, low-seasonality regimes are dominated by organisms that can grow at low nutrient concentrations, and are suited to oligotrophic conditions.
Phytoplankton absorb light at different wavelengths depending on the types of light-harvesting pigments they contain. By resolving the full light spectrum in the model we are able to incorporate these characteristics and investigate their importance in driving phytoplankton distributions in the ocean.
A central goal of biology is to understand feedbacks between the environments and the genotypes of organisms. Picocyanobacteria dominating open oceans differ in their abilities to utilize nitrate, nitrite and ammonium. We modeled selective pressures on these nitrogen use abilities in a detailed global ocean, and found that the selective consequences of losing nitrate use abilities were weakest in tropical oligotrophic regions, where non-nitrate using ecotypes of Prochlorococcus are abundant in the real world.
We explore the diversity of marine nitrogen fixers, or diazotrophs, as well as the factors that control their habitat in a global ocean model. Analogs of Trichodesmium, unicellular cyanobacteria and diatom-diazotroph associations occupy habitats consistent with those observed in the ocean, confined to tropical and subtropical waters. In the model’s South Pacific, diazotroph abundance is extremely sensitive to the delivery of iron and parameterization of its biogeochemical cycle.
It is clear that the size of unicellular organisms can have important consequences for nutrient and light acquisition and metabolic rates. We have used idealized theoretical approaches to understand the consequences of empirically constrained relationships between key phytoplankton traits and cell size for fitness and the organization of microbial communities.
We have performed an eddy-permitting global integration of the self-assembling ecosystem model. This simulation is unique in its resolution of both fine scale ocean features and phytoplankton species. The physical setup is that of ECCO2 on a cubed sphere (PDF), with a nominal horizontal resolution of 18km and 50 vertical levels.