Coral reefs thrive in shallow, brightly-lit waters, so the amount of sunlight reaching the sea floor (called ‘benthic irradiance’) in a reef area can be used as a critical indicator for ecosystem health.

Sediment and other water quality impacts can reduce benthic irradiance, which can have wide-ranging impacts on coral, including slower growth and recovery from disturbance.

A project at the Tropical Water Quality Hub will model 14 years of benthic irradiance (at an almost daily frequency) across the entire Great Barrier Reef.

Project 2.3.1, led by Dr Katharina Fabricius at the Australian Institute of Marine Science (AIMS), in cooperation with NASA, will investigate what determines the loss in irradiance [or light], including river discharges and other point-source events.

Dr Fabricius said processing the massive amounts of MODIS satellite data was ‘not a trivial task’. “There is a huge amount of number-crunching involved,” she said.

“Our challenge is developing an algorithm to quantify how much light energy is reaching the corals in that area, and to work out the critical light thresholds to support reef health. In parallel, we are running a light exposure experiment at AIMS’ National Sea Simulator, to validate these thresholds.

“There are a lot of drivers for benthic irradiance – depth, day length, sun angle, wind, cloud cover and other natural factors need to be corrected for, then you can start looking at runoff and sediment.”

The project aims to develop a new tool that will allow us to measure from space the status and trends of water quality, and to interpret it in the context of its effects on coral reef health.


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