University of Tasmania, Australia

Taxonomic changes in Southern Ocean phytoplankton.

Level: PhD

How are populations of Southern Ocean phytoplankton and microzooplankton structured, and have communities changed in response to climate?

Phytoplankton form the base of Southern Ocean food webs –supporting all life in the Southern Ocean – and they are crucially important in removing CO2 from the atmosphere by capturing and directly or indirectly transporting carbon to the ocean’s interior via the biological pump. They are also sensitive to environmental conditions, notably temperature, nutrients, light, mixed layer depth, and ocean acidification. Thus they are excellent indicators of changes in such factors due to climate change.

The species composition of the phytoplankton community determines factors such as the size spectrum, nutritional value, productivity, and sinking rates, thereby influencing biogeochemistry and the availability of food for the rest of the food web. Thus it is vital to determine the species composition in order to model the phytoplankton at a regional level. Also, changes in species composition or range are likely to be amongst the earliest detectable effects of climate change.

This project will investigate the species composition of phytoplankton and protozoa in the Southern Ocean using samples collected from 2002 to the present from the French vessel l’Astrolabe, which traverses between Hobart and Dumont d’Urville 3-4 times per year. It will be based around microscopic examination of whole water samples and samples collected with a 20 µm net (the latter collects only larger cells but samples are comparable with those collected using similar technology in the 1930s). Considerable environmental and pigment data exists to supplement the microscopy in statistical analysis.  A previous honours project has already indentified that, like the Arctic, the keystone species Emiliania huxleyi has significant increased its latitudinal range since the 1980s.

The aim of the project will be to distinguish phytoplankton/protozoan communities and to determine where, when and under what conditions they occur. It will also compare current data with historic data to determine whether changes have occurred. The project can start immediately.

Supervisors: Simon Wright and Andrew Davidson