AbstractCorals can potentially provide years or possibly centuries of information on trace element concentrations and reef health. However, coral bio-monitoring studies have been limited by a lack of understanding of coral calcification mechanisms. In addition almost all studies have been performed in impacted environments on a small number of different species. This study aimed to broaden the applicability of coral bio-monitoring showing that, Favids (Goniastrea aspera and Platygyra sinensis), may be used to monitor reef health and trace element concentrations in near pristine, fringing reef environments.
During the initial analysis it was confirmed that Goniastrea aspera and Platygyra sinensis contained readily datable annual density bands despite the small seasonal differences in SST and the stressful conditions experienced in Darwin Harbour. Goniastra aspera and P. sinensis corals responded to environmental stressors, showing reduced tissue layer thickness, extension and calcification rates at the most freshwater and sediment affected sites. These analyses included the first study of tissue layer thickness measurements in Favid corals.
Favids from all zones in Darwin Harbour and Heron Island also showed clear declines in calcification rate over the study period (1994-2003), possibly due to ocean acidification. This decline is in agreement with a decline attributed to ocean acidification on the northern – GBR. Favids were also found to be well adapted to the harsh fringing reef environment of Darwin Harbour in contrast to Porites spp., which were almost completely absent from Darwin Harbour intertidal reefs.
Using distribution coefficients calculated from elemental analyses of Favids and seawater it was concluded that copper, manganese and lead are taken up by corals without significant bio-regulation and are most likely aragonite bound, whilst aluminium is discriminated against and zinc is possibly bioaccumulated. Coral trace element concentrations were also found to agree with seawater and sediment concentrations indicating the presence of low level metal pollution in the slightly impacted, Darwin city and wharf foreshore areas. However, the majority of Darwin Harbour was found to be near pristine, with little change occurring over the last ~100years.
This study has shown that G. aspera and P. sinensis corals are useful bio-monitors of environmental health, and may also provide reliable trace element records provided that trace element uptake and incorporation is understood for the specific trace elements analysed.
|Date of Award||Nov 2011|
|Supervisor||David Parry (Supervisor), Niels Munksgaard (Supervisor) & Janice M. Lough (Supervisor)|