‘Like planting a seedling’: JCU discovery buoys coral survival rates

New James Cook University research reveals similarities between growing coral and growing plants, which could prove crucial in the fight to protect the reef.

James Cook University senior research officer and lecturer Hillary Smith

Corals seeded into terracotta tiles and placed into reefs are more likely to survive than naturally growing corals at one year old, a new study led by James Cook ­University has found.

Coral also had a greater survival rate when seaweed was manually removed from reefs, similar to the process of weeding in gardens.

“Just like planting a seedling in a small flowerpot and plucking weeds, the same strategies seem to benefit baby corals,” said JCU senior research officer and lecturer Hillary Smith.

Ms Smith, who is also a University of NSW candidate, said the findings were important as coral reefs continued to “degrade under human pressure” and strategies were needed to overcome high mortality rates in early life stages.

“Coral seeding devices worked best when paired with sea-­weeding, or removal of overgrown macro-algae at this reef,” she said of the findings published in the Journal of Environmental Management.

Seeding using the specialised ceramic devices work best for reefs that have “suffered catastrophic and acute losses in adult populations and/or lack larval supply”, the study notes.

The effects dwindled beyond the first year, however, while costs remained high, with the study suggesting the need to “significantly reduce per-unit coral seeding costs” to make it scalable.

The current cost of deploying 120 seeding devices was more than $US25,000, or about $423 per surviving colony. This is about $17m per hectare, which is high compared to other reef restoration methods such as transplantation, coral gardening, larval enhancement, and substrate enhancement, which have a median cost of $400,000 per hectare.

“Our results show that survival of seeded corals needs to be monitored over multiple years to understand if the method has long-term ecological benefits,” Ms Smith said.

“We found that sea-weeding combined with seeding can give young corals a crucial head start, but it’s not a silver bullet. Long-term survival depends on many site-specific factors, and restoration strategies need to be tailored accordingly.”

The study notes: “While devices initially increased coral survival, the approach is currently expensive and the ecological benefits, if achieved, are only likely to be realised over long time periods (eg five to 10 years), highlighting the need for research on longer-term deployments.”