Science update
Science Update5 April 2000
The SE Qld Regional Water Quality Management Strategy has been
investigating possible causes of the bloom, through the work of a Task Force
headed by Associate Professor Bill Dennison of the University of Queensland
Marine Botany. This work is being funded by the Commonwealth Government Australian
Research Council, South East Queensland Councils and the Queensland Environmental
Protection Agency. A copy of the Lyngbya newsletter can be viewed by
clicking here.
Ecophysiology
The current bloom in Deception Bay returned in mid January this year after a
13 month absence.
High water temperatures of over 24°C appear to have assisted the growth
of the cyanobacteria over the summer months and data collected has recorded
over 8km2 of the toxic bloom within the Deception Bay region. A large bloom
covering approximately 30 km2 was reported in March this year on Amity Banks.
This is in excess of previous blooms recorded within Moreton Bay.
Lyngbya appears to be tolerant of a wide range of salinity; significant decreases in productivity have been observed at salinities between 0ppt and 9ppt but rapid recovery of the cyanobacteria was observed when salinity was raised.
Lyngbya fixes nitrogen from the atmosphere and high rates of nitrogen fixation have been observed in the bloom areas.
The cyanobacteria bloom has a very rapid expansion rate and measures of bloom photosynthesis are among the highest recorded for a benthic marine organism.
Iron Chemistry
Studies indicate a clear distinction between the chemical properties of offshore
waters and those within the vicinity of the bloom in Pumicestone Passage. These
waters differ in terms of humic acid (eg. tannin content) and iron chemistry.
Sites inshore (and near the bloom) have higher humic acid (organics) (approximately
1.8-10mg/L) compared with offshore levels (approximately 0.1-1.6 mg/L). Fe (II)
is likely to be the major form of iron taken up by Lyngbya. Available information
indicates that higher organic material from land run-off lead to more bioavailable
iron. Further links are being investigated.
Toxicology
Toxicological tests have shown a direct link between Lyngbya and dermatitis.
People encountering Lyngbya are urged to avoid it and not pick up or
touch the bloom whether in the water or washed up on beaches. At least three
known toxins have been identified from the Moreton Bay Lyngbya populations
including:
- Lyngbyatoxin (dermatitis and tumor promoter);
- Aplysiatoxin (tumor promoter); and
- Debromaplysiatoxin (dermatitis and tumor promoter).
Variations in toxicity have been measured between samples collected the 2 main
affected areas, and studies are underway to determine the population structure
and origin within Moreton Bay. An epidemiological study is currently under way
to determine further effects of the cyanobacteria.
Molecular Biology
Molecular Biology is also being studied to further determine possible triggers
of the Lyngbya bloom. In samples taken from Deception Bay a particular
form of the nif gene has been identified. This is significant as the nif gene
(which has a role in nitrogen fixation) has shown to be responsive to Fe nutrition.
This gene may serve as an appropriate marker for Fe stress in the environment.
This information may also help to determine population structure and origin.
A conceptual model has been developed to explain current understanding and thoughts
about Lyngbya blooms. Research is currently aimed at testing this model to enhance
our understanding of Lyngbya blooms.
This information is kindly provided by the SE Qld Regional Water Quality Management
Strategy. For further information please contact Associate Professor Bill Dennison
through the SE Qld Regional Water Quality Management Strategy on (07) 3403 4206.
Last updated: 18 October 2004
