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Healthy coral populations produce a surprising number of offspring

Wiley

Healthy coral populations can produce up to 200 times more juvenile corals than degraded coral populations nearby, according to a new study in Conservation Letters. By studying one of the Caribbean's healthiest remaining coral reefs on the island of Curaçao, researchers found that healthy coral populations had a higher percentage of successful parents and each parent produced up to four times more offspring compared with corals in degraded populations. Combined with higher coral numbers overall, the healthy populations produced up 200 times more offspring per square meter of coral reef.

The conservation value of healthy coral reefs is therefore higher than previously thought because of their outsized contributions to coral reproduction and reef recovery. Traditionally, coral abundance was the most widely-used method for assessing reef health. This new study shows this measurement underestimates the hidden differences in reproduction between healthy and degraded reefs. Because coral offspring can swim and disperse to other reefs, the healthiest remaining coral reefs can help re-seed and regrow coral reefs on local and regional scales.

"Healthy reefs are critical nurseries for baby corals and they support the recovery of coral communities elsewhere," said lead author Dr. Aaron Hartmann.

The reef area studied, known as Oostpunt, was recently ranked among the three healthiest coral reef ecosystems in the Caribbean by an IUCN study of the entire region. The Oostpunt area is undeveloped, yet the island of Curaçao is currently considering a plan to build over 2,000 hotel rooms, 18,000 residences, 3 golf courses, and their supporting infrastructure directly on the coastline. The new study shows that significant ecological damage is likely to occur island-wide due to the loss of high levels of coral reproduction from this thriving, undeveloped reef region.

"The coral reefs at Oostpunt represent a window into the past when Caribbean reefs were healthy and vibrant everywhere. We've identified an explanation for why Oostpunt's reefs have remained this way - healthy parents there make lots of babies, while stressed parents on other reefs don't," said Hartmann.

The researchers also found that corals in healthy populations contain greater amounts of fats, which allow them to produce more offspring, and that corals in healthier populations make more babies per parent without reducing their investment in each offspring.

Coral reefs are worth US$1T per year in fisheries production, shoreline protection, job creation, tourism and drug discovery potential. The survival and recovery of these systems depends on the production and long-distance dispersal of coral larvae.

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