Dredging Science: Understanding how low light levels can affect coral health

Research has confirmed that some coral and important reef building algae can sustain being exposed to low light conditions for up to 10 consecutive days before their health is critically affected.

The findings have important implications for the environmental impact assessment and management of dredging operations, which cause sediment plumes.

The results of the Western Australian Marine Science Institution’s Dredging Science Node research, conducted in specially developed tank systems at the AIMS National Sea Simulator (SeaSim), have been published in Scientific Reports.

Lead researcher Pia Bessell-Browne from The University of Western Australia Oceans Institute, Centre for Microscopy, Characterisation and Analysis and Australian Institute of Marine Science said corals and important reef building algae are particularly susceptible to light limitation resulting from elevated sediment particles in the water column which can be generated by naturally occurring events, such as cyclones, as well as coastal development activities such as dredging.


Experimental tank set up at the AIMS National Sea Simulator used to determine the impacts of 6 light levels on both coral and algal health. (SeaSim)


“This study has determined light levels that need to be maintained in order to reduce negative impacts on the health of coral and reef building algae,” Ms Bessell-Browne explained. “When corals do not receive adequate light, the algae that live within their tissues and provide them with up to 90 per cent of their daily energy requirements leave, meaning the corals are without their main food source and can starve if this condition is maintained over extended time frames.”

A range of low light levels were investigated and their impacts on several species of corals, along with juvenile corals and a species of reef building algae were determined.


Photographs of representative A. millepora and P. acuta fragments after 30 d of exposure to the six daily light integral (DLI) irradiance treatments of ~0, 0.02, 0.1, 0.4, 1.1 and 4.3 mol photons m−2 d−1 (Bessel-Browne et al., (2007))


“The results demonstrate that both corals and algae are sensitive to exposure to low light conditions for more than 10 consecutive days,” Ms Bessell-Browne said. “Juvenile and adult corals have similar low light tolerance, while the reef building algae is more sensitive to the low light conditions than the corals.”

The thresholds determined by these research findings are expected to contribute to the environmental impact assessment and management of dredge programs where these coral and algae species occur in the field.

Bessell-Browne P, Negri A.P., Fisher R, Clode P.L., Jones R (2017) Impacts of light limitation on corals and crustose coralline algae Scientific Reports doi:10.1038/s41598-017-11783-z


The WAMSI Dredging Science Node is made possible through $9.5 million invested by Woodside, Chevron and BHP as environmental offsets. A further $9.5 million has been co-invested by the WAMSI Joint Venture partners, adding significantly more value to this initial industry investment. The node is also supported through critical data provided by Chevron, Woodside and Rio Tinto Iron Ore.


Dredging Science