Marine Microbial Ecology

What are we studying?

The Australian Antarctic Division marine microbial programs focus on:

What is there?

Identifying the biodiversity of Southern Ocean protist populations.

A guide to more than 450 Antarctic protists with photographs and descriptions is being compiled, as an aid to the identification of these organisms. New organisms are being found and described every year.

Where and how much?

Determining the distribution and abundance of protists in the Southern Ocean.

The distribution, abundance and types of phytoplankton present are being determined using their photosynthetic pigments, by light and electron microscopy, and using electronic particle counters. Factors that control population abundance are being studied in relation to oceanography, nutrients and grazers - information vital to models of global carbon budgets. We are also investigating associations between species and ecological processes or oceanic regimes.

Distribution of chlorophyll a near the Antarctic coast, integrated to 150m depth.

Vertical distribution of chlorophyll (mg.m-3) in the top 200m along a north-south transect off Antarctica. Ice cover is shown at top left. ASF = Antarctic Slope Front where cold (-2°C) coastal water meets warmer (1°C) oceanic water. Tmin = temperature minimum layer.

What are they doing?

Determining the response of protist populations to enhanced ultraviolet radiation due to the Antarctic ozone hole.

Protists in the upper waters of the ocean are exposed to increased ultraviolet radiation (UV) at the time of the "spring bloom". Different species vary in their susceptibility to damage by UV, and changes of species composition have been observed in Antarctic protist communities. Such changes directly affect the abundance and nature of food available to larger organisms as well as the extent of CO₂ uptake in surface waters.

Determining the feeding rates and preferences of protozoa.

Measurements are being made of the rates of protozoan feeding in the Southern Ocean, as well as studies of their feeding selectivity. Protozoan preference for food of particular sizes and "flavours" affects their role in the microbial loop.

Determining the abundance, viability and activity of marine bacteria.

These programs link with external programs in which scientists measure phytoplankton production, carbon dioxide uptake, carbon sedimentation, nutrient concentrations and oceanography to build an integrated picture of the smallest, but the most important, components of the marine food web.

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