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Pining for the Fiords

Fiordland's renowned black coral will be among the species spotlighted in a major new study by the Department of Marine Science at Otago University.

The Department has signed a contract with the Electricity Corporation of New Zealand to conduct the first-ever long-term research into the ecological processes at work in Doubtful and Milford Sounds.

The seven-year project will monitor the effects on marine life of freshwater discharge from ECNZ's Manapouri Power Station into Doubtful Sound. Comparative information will also be collected from research at Milford Sound, which will be used as a reference fiord.

The data collected will be used for research and teaching purposes and provide ECNZ with information on the possible effects of freshwater flow from the power station into Doubtful Sound. ECNZ must conduct a research and monitoring programme, under its present consent, to continue to discharge water into the Sound.

The main aim of the project is to ensure that the current operation and any further development of the power station will not impact adversely on the environment, says Marine Science Head of Department, Professor Philip Mladenov.

"Before the Manapouri Power Station was commissioned in 1969, no baseline studies had been done," Mladenov explains. "It was therefore difficult to determine what impacts might have taken place because of the absence of data. Now, with the collection of this long-term data, we will be better positioned to determine if discharging more water might pose a threat to marine life."

Mladenov says black coral is likely to be very sensitive to any changes in the fiords and should therefore be a useful indicator of the possible effects of freshwater discharge on the marine environment [In the Coral Sea, June 97].

"We have tagged more than 130 black coral colonies and will follow their health over many years, which will give us a picture of each colony and what's happening to it. People are also interested in how old the colonies are -- they could be several hundred years old -- and our research will give us precise information on their growth rates."

Five instrument-carrying mooring systems are being positioned in the Sounds -- four in Doubtful Sound and one in Milford Sound. The systems consist of a 250 kg anchor linked to a surface buoy by a cable, to which the instruments are attached. The instruments will monitor physical changes in the fiords on an hourly basis -- measuring water temperature, salinity, currents and light levels. This information will be stored in a data logger inside the buoy, which is equipped with a solar panel, radar reflector and light.

Marine Science researchers will visit the buoys every three months, plug their computers into the buoy system and download the data. They will then examine how the various factors change according to power station discharge, rainfall and other weather events.

Similar data will be collected from Milford Sound, which will be the "reference site" for the project, ensuring a cross-check of the Doubtful Sound data against naturally occurring variations.

One possible change resulting from power station discharge is an increase in the thickness of the low salinity surface layer in the fiord.

Says Mladenov: "The water is quite fresh in this layer. If it gets unusually deep for some reason -- for example, because of a combination of high power station discharge and heavy rainfall -- it might contact certain species (like black coral) living on the rock walls which are not accustomed to freshwater, and harm them."

Other species which may be at risk from increased freshwater discharge include red coral and other invertebrates, such as brachiopods.

Mladenov stresses that the project's teaching and research applications are just as important as the "considerable" commercial benefits for the university. He expects the study will produce data on how the fiords function and involve many graduate students in research work.