The use of living organisms as an indicator for pollution is not a new concept – nearly a century ago the use of 'coal mine canaries' began. These birds were used to detect the colourless, odourless, tasteless and potentially fatal carbon monoxide gas often present in mines...
Macroalgae as environmental indicators
In Antarctica we are using living creatures fixed to the ocean floor as our 'canaries', they are macroalgae, more commonly known as seaweeds. Signs of stress in macroalgae because of pollution are generally not visible to the naked eye. Stress, however, is measurable using equipment specifically developed to monitor the plant's ability to use life-giving energy from the sun.
Shirley Island: abundant macroalgae in an exposed high-light location
Photo: John Runcie
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Diving under the fast ice off the coast near Casey
Photo: John Runcie
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Equipment set up to measure the health of seaweeds
Photo: John Runcie
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Why are we focussing on seaweeds?
The marine sea-bed communities in Brown Bay, adjacent to the abandoned waste tip in Thala Valley near Casey Station are very different from those at other locations in the area. One of the most striking differences is that seaweeds are virtually absent from Brown Bay. Our studies with the PAM will help us understand whether seaweeds are absent from that site for natural reasons or whether their absence is caused by contamination.
Light absorption and fluorescence
Plants receive radiant energy from the sun and use it to convert carbon dioxide and water into sugar or food, during photosynthesis. Within the plant, chlorophyll a absorbs light energy of specific wavelengths and uses most of this energy to do photosynthetic work (photochemistry) or redirects excess energy to heat dissipation (protection against damage caused by high light). A small portion is re-emitted as fluorescence. Those wavelengths that are re-emitted can be easily measured using fluorometery techniques. The Pulse Amplitude Modulation (PAM) fluorometers designed by the German company Walz are designed to operate in sunlight, and use a signal modulation technique to eliminate background noise from the reflected sunlight.
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| Light energy absorbed by chlorophyll a and redirected into fluorescence, heat dissipation and photochemistry. |
Making seaweeds speak with fluorescence
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Fluorescence of a macroalgae being measured in the laboratory. Half of this plant has been exposed to a pollutant.
Photo: John Runcie
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A healthy plant capably absorbs light from the sun, and directs a proportion of the energy absorbed to photosynthesis. Generally, the maximum possible proportion is slightly above 80%; that is of all the light received by the plant, 80% is directed to photosynthesis. This proportion is determined by providing a very bright pulse of light and determining the difference between minimal and maximal fluorescence. Any decline in this proportion indicates a reduction in the efficiency with which light is converted to photosynthetic product (e.g. growth or reproductive output), and such a decline is often seen when a plant is stressed. So when plants becomes exposed to pollutants (heavy metals, petrochemicals) or are otherwise stressed, they are often less able to convert sunlight into photosynthetic product and this stress can be detected using fluorescence.
Fluorometers that use the PAM technique work by rapidly sending brief pulses of light to a plant. A healthy plant responds to this light very quickly (within microseconds) by re-emitting some of the light energy as fluorescence which is detected by the fluorometer. PAM fluorometers are designed to measure only the light that is changing quickly (it does not read the slow changing, ambient, or background light).
Macroalgae are extremely sensitive indicators to environmental pollution
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How does a PAM work?
The amount of returned light (fluorescence) under normal conditions from a plant is very small. Small enough in fact, to be 'swamped' by the ambient, or background light from the sun. PAM technology is able to overcome this by bombarding the macroalgae with very fast pulses of light that can be absorbed by chlorophyll a. A healthy plant is able to respond to this fast, intense illumination. The electronics of the PAM filters the light that it receives to read only the light that is changing very quickly, thereby filtering out the slow changing, ambient light.
Innovation of the octopam
Working in Antarctic conditions can be very challenging. Diving is often not possible because of strong winds or bad weather. In an attempt to collect multiple, unattended readings, the multi-channel fluorometer was developed.
The PAM technique for measuring fluorescence in sunlight has been around for many decades and the increasing use of PAM fluorometers around the world has been largely due to instrumentation developed by the German company Walz. The Diving-PAM, a Walz fluorometer, was used extensively by ANARE in 2001-02 at Casey station, however its use was restricted to single dives and it was unable to provide information about changes in algal health over a 24 hour period. Engineers and technicians of Science Technical Support worked closely with scientists from the Human Impacts research program to adapt existing PAM technology to produce a world first; a device that can simultaneously measure chlorophyll fluorescence of eight separate plants underwater 24 hours a day, without user intervention. Previously these instruments would require an operator and their use was generally limited to daylight hours and good weather.
Underwater housing of Octopam, in the foreground is the 8-way blue light source and its underwater connector.
Photo: Warren Nicholas
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The completed octopam on the sea ice at Sparkes Bay.
Photo: John Runcie
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The arms of the octopam spread out over a number of macroalgae
Photo: John Runcie
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Science Technical Support adapted the simple Junior-PAM (Gademann Instruments, GmbH) for use in a waterproof, robust and remotely operated module. The Junior-PAM is positioned within the housing on a rotating spindle so that it sequentially shines its measuring light down eight flexible "light pipes" that are directed on individual marine plant samples. This multi-channel device, otherwise known as the Octopam as it has eight arms – was still under development when it left on a ship bound for Casey Station in late 2002. Telecommunications and innovation by the engineers in Australia and the science and support staff in Antarctica resulted in a fine product. Early results were encouraging and the Octopam will be further developed to gain an even greater amount of results in future season.
Excavating contaminated material from Thala Valley
Photo: H. Cook
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To the future
- For Casey this season (2004-05) a programmable single-channel fluorometer is being developed that can be set up in different combinations and at different depths under the water to provide many more opportunities for measurement. These devices have a novel feature that enables them to exclude external light during the measurement.
- Information gained from this research will contribute towards the development of Antarctic water quality guidelines.
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