Corals count on nearby neighbors for successful reproduction

A recent study highlights a critical challenge for coral reproduction in the face of climate change. Led by Professor Peter Mumby from The University of Queensland, the research found that corals must be within a few meters of each other to reproduce successfully.

This surprising discovery has significant implications for coral survival, as warming oceans and other climate impacts continue to decimate reefs.

Factors in coral reproduction

The research team measured the success of a natural coral spawning event in March this year.

“In what came as a surprise, we saw that corals needed to be within 10 metres (32.8 feet) of one another, and preferably closer than that for fertilization to take place,” explained Professor Mumby.

The team’s findings revealed a stark reality. Fertilization rates averaged 30% when corals were very close to each other. However, this figure dropped to less than 10% at a separation of 10 meters (32.8 feet) and was virtually zero at distances beyond 20 meters (65.6 feet).

“We knew corals couldn’t be too far apart, but we found they need to be closer than we’d expected,” noted Professor Mumby.

“Climate change impacts like bleaching are killing and reducing the density of corals, so we’re concerned that individuals may end up too far apart to reproduce successfully.”

Importance of proximity in coral reproduction

The research team set up their experiment on a reef in Palau, Micronesia. They placed containers above 26 coral colonies during a spawning event, capturing eggs and allowing sperm from nearby corals to enter the containers.

“The containers captured some of each corals’ eggs and drifted to the surface where they followed the tide,” said Professor Mumby.

“Although the eggs could not escape, sperm could enter the container and fertilize the eggs. After an hour of drifting, the proportion of fertilized eggs was noted for each type of coral, along with the distance to similar established corals.”

The results demonstrated the importance of proximity among corals for successful reproduction.

Implications for coral survival

The findings from The University of Queensland highlight how climate change exacerbates challenges for coral populations. Bleaching events and other stressors not only kill corals but also reduce their density, making reproduction increasingly difficult.

Dr. Christopher Doropoulos from CSIRO, a co-author of the study, emphasized the importance of coral reproduction for population resilience and evolution.

“In the future, we may need to help corals continue this key part of their lives,” said Dr. Doropoulos. “Understanding the importance of local neighbourhoods provides tangible targets for interventions like coral restoration.”

Restoration efforts and future directions

Coral restoration emerges as a vital strategy to combat this reproductive challenge.

“Ideally, the density of corals would be monitored at important locations and restoration carried out to return the density back to the levels required for successful reproduction,” Dr. Doropoulos added.

Professor Mumby highlighted the significance of ongoing restoration efforts.

“Our work over the past 5 years on the Great Barrier Reef through the Reef Restoration and Adaptation Program is also helping to define these critical thresholds to help restoration practitioners set targets for density to help maintain coral populations,” said Professor Mumby.

The study, funded by the McCusker Foundation and the Australian Government’s Reef Restoration & Adaptation Program, provides actionable insights for coral conservation.

By identifying critical density thresholds, researchers hope to guide interventions that can enhance coral reproduction and resilience.

Hope amidst challenges

This research highlights how vulnerable coral populations are, and emphasizes the critical need for focused conservation efforts.

Climate change, through factors like ocean warming and bleaching, is making coral survival increasingly difficult. However, studies like this provide essential insights for scientists and conservationists to better protect coral reefs.

The key finding – that corals need to be close to each other for reproduction – can guide efforts to ensure they remain healthy and viable. If corals are not able to reproduce due to greater distances between them, it could lead to the decline of these vital ecosystems.

Ensuring corals are sufficiently close for successful reproduction is therefore crucial in maintaining and preserving coral reefs for the future.

The study is published in the journal Proceedings of the National Academy of Sciences.

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