Earthwatch - JCU

Yunbenun (Magnetic Island), Australia

A coral reef with various types of coral and marine life, with a measuring tape running across the center to mark a plot. The left side shows a reef overgrown with seaweed and the right shows a reef where sea-weeding has restored the reef.
A map of the world centered on Australia, showing the location of Magnetic Island on the Great Barrier Reef.

At Yunbenun, scientific research on sea-weeding has been ongoing since 2018. The site is a collaboration between James Cook University scientists and Earthwatch Australia.


Our Story

Yunbenun reefs are dominated by benthic Sargassum spp.

Yunbenun (Magnetic Island) is located in the central inshore region of Australia’s Great Barrier Reef. Approximately 10km from the city of Townsville, it is home to diverse fringing coral reefs, mangroves, and seagrass beds. Townsville hosts a major shipping port which was established in the 1880s, and dredging since its establishment has led to increased sedimentation of the reefs surrounding Yunbenun. Combined with cyclones, flooding, and mass bleaching, the reefs of Yunbenun have showed a long-term shift toward macroalgae dominance, primarily Sargassum spp. Multiple lines of evidence support this shift, including historic archives, eDNA derived from sediment cores, repeat benthic monitoring, and oral histories.

This sea-weeding site was established in 2018 as a collaboration between James Cook University (led by Professor David Bourne and Hillary Smith) and Earthwatch Australia.

What we're doing

Understanding the pros and cons of weeding

The research at Yunbenun has examined the long-term ecological impacts of weeding, along with trying to determine the best timing and frequency of intervention. The site has twelve 5m x 5m plots established in each of two bays, with six plots in each bay being controls (left untouched) and six plots as intervention (weeded). Weeding is done manually alongside citizen scientists from Earthwatch twice per year - once right before coral spawning, and once around when the macroalgae reproduce and senesce. The team has monitored a long list of metrics, aiming to understand not only if weeding works for restoration of corals, but how it affects other elements of the ecosystem to ensure there are no unintended consequences. The metrics monitored include: benthic cover, coral recruitment, coral juvenile density, algal density and canopy height, coral bleaching risk and recovery, fish communities (visual surveys and eDNA), rubble-associated invertebrate communities (using RUBS and eDNA), micro-benthic community succession, sediment deposition, turf algae growth, hydrodynamics, and the impact of disturbances (heatwaves, floods, and cyclones) on restoration success. The site has also hosted research investigating synergies between sea-weeding and other restoration methods (e.g., coral seeding).

What we've found

Sea-weeding restores coral cover and diversity

Since 2018, the team has removed over 3000 kg of seaweed from the experimental plots at Yunbenun. And in response, the reef has thrived. While it took a few years of effort, coral cover skyrocketed from a starting point of 5-8% cover to over 60% cover. Excitingly, coral diversity also increased. While most restoration methods focus on one or a few species, sea-weeding seems to benefit a wide range of corals, restoring diverse functions and habitats to the reef. Many of the research findings have already been published (see below), but please reach out if you’d like to hear how other elements are progressing.

Stay tuned for more updates from our project!

Research outputs

Press coverage