Underwater Sea-Weeding

Globally, coral reefs are under increasing threats from ocean acidification, increases in runoff pollution and warming seawater temperatures. Inshore coral reefs of Magnetic Island and throughout the Great Barrier Reef Marine Park are dominated by macroalgae (commonly known as ‘seaweed’) but the direct cause of this ‘take over’ is not well understood. Macroalgal removal has been proposed as a potential intervention to aid active reef recovery through reduced competition for resources and increased substrate availability for coral larvae to settle.

In light of the current threats to coral reef systems, it is important to investigate the effectiveness of active reef recovery action. Can active interventions support the recovery of the Great Barrier Reef?

To find out, Earth Watch Australia has teamed with Lead Scientist Dr David Bourne from the Australian Institute of Marine Science and several marine scientists at James Cook University (JCU) to identify best-practice methods for coral recovery.

This past week (21-25th October 2020), two volunteers (including conservation photographer, Miranda Fittock) and I, joined an Earth Watch Expedition, Recovery of the Great Barrier Reef, on Magnetic Island off the coast of Townsville.

What we did:

Each morning we put on our wetsuits and dive weights and swam out into set locations within Arthur Bay or travelled by boat into Florence Bay. SCUBA divers descended to the seafloor which was between 2-4.5 m deep depending on the tides and started to remove the macroalgae. The divers put the macroalgae into bags and so it was the job of the volunteers (the snorkelers) to free dive to the divers and replace their full bags with empty ones. This saved both time and air for the SCUBA divers who would otherwise have to make continual trips to the surface. The full bags of algae were quite heavy so we put them in floating baskets and swam them to the research boat to be weighed.

Miranda snapped this picture of me free-diving down to the measured-out plots to remove macroalgae

Holding our breath and carrying heavy bags of algae was quite challenging but we all became comfortable and efficient by the end of the week!

As a team we managed to remove a whopping 376 kgs from the reef in just a few days!

The bags of algae were heavy so we swam them to the research boat in floating baskets to be weighed

Where to next?

While the volunteers returned home, the marine scientists are going to continue their research by monitoring the differences in coral growth between the plots with macroalgae and the plots where we removed the algae. Soon after the coral spawning in early November, juvenille corals will be swimming around looking for a suitable place to grow. We need to wait and see if the baby corals prefer the plots with or without algae.

What can YOU do?

Participate as I did! Earthwatch run a range of expeditions year-round. More information can be found here.

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