Coral Human impacts

Just Put on the Market: Ideal for Coral Reef Development

Scientists Identify Best Spots for Reef Restoration

Coral reefs have been front and center in the news lately, as rising temperatures, increased acidity, and nutrient pollution cause mass bleaching events and scientists lament losses they say mark the “death” of coral reefs around the world. Conservation superstars have even weighed in on the issue; Suzuki, the Cousteau family, and the usually up-beat Attenborough have all made multiple public calls for action to turn the tide on an issue that affects every person on Earth. With international fisheries, coastal settlements, and multi-billion dollar tourism industries at stake, scientists are scrambling to find new solutions that could slow or reverse the exponential loss of corals and the goods and services they provide. The latest include genetic engineering, 3D printing, and artificial reef substrates. Together, they could give individual coral species and individual populations a fighting chance at surviving and reproducing through disturbances that would otherwise cause bleaching and ecosystem collapse.

Satellite image of the Great Barrier Reef off of Queensland (retrieved from Wikipedia, photo by NASA).

Without strategic prioritization however, many of these innovative conservation tools may be ineffective at restoring corals in environments facing many hardships. Recreating every single coral reef is simply impossible, not only because it’s expensive but also because there are few places in the ocean that experience only one human-caused stressor. What’s the point in restoring a reef if it’s just going to disappear the following year, choked by high temperatures or pollution? To successfully save the coral reefs, each species, population, and community needs to be resilient to changes over time. This leads us to the question, where should we focus our efforts?

Hock et. al. suggest focusing on reefs most likely to contribute to wider ecosystem rehabilitation. They list three criteria necessary for maximizing the chance of individual reefs contributing to the restoration of the whole system: 1) a source population is needed to supply other populations with the genetic material to create new corals, and this transfer of resources from the source population to others needs to be consistent through time, 2) this source population must experience lower exposure to disturbances compared to others in the system, so that it can maintain its adult stock required to initiate recovery of the other populations, and 3) the source population must only share desirable resources with the outside populations, such as sex cells or larval corals, and not share undesirables, like disease, pests, or invasive species. Reefs that meet all three of these criteria offer the greatest resilience to the wider coral reef system by facilitating the fastest and most likely-to-be-successful recovery after disturbance.

To identify these reefs, the researchers explored the connectivity and profiled disturbances in the world’s largest coral reef system, the Great Barrier Reef. Here, corals are plagued by both bleaching events and the invasive Crown-of-Thorns Starfish and have experienced significant declines in recent decades.

Left is a healthy fire coral, while on the right is a fire coral that has “bleached” itself due to environmental stressors. (Source:

Hock et. al. found a few reefs in the Great Barrier system that experience low disturbance and are just connected to neighboring reefs enough that they could serve as a source of genetic material while not promoting the spread of the invasive Crown-of-Thorns. Over 500 reefs (14%) met the criteria of being good consistent sources of new corals, being relatively close to their neighbors, while just over 1,000 reefs (33%) appeared to be naturally resilient against thermal stress, and about half of these met both the first and second criteria. The third criteria is where the number takes a dip, in reefs that don’t also supply their neighbors with larvae of the invasive Crown-of-Thorns. Because both coral and starfish larvae are transported to new reefs via ocean currents, reefs that could supply new coral stock are also likely to promote invasion by the foreign starfish. To avoid this, the source reefs have to have a low likelihood of accumulating the starfish themselves. These reefs are upstream of the currents that transport larvae to other reefs, which are inward towards the land. Hock et. al. found that about half of the 500 well-connected reefs met this criteria, being upstream enough that they are likely to distribute released coral larvae while not accumulating (and therefore not distributing) starfish larvae. Nearly 100 reefs met all three criteria.

Beach cleanups are one way we can make a positive impact on our coasts. (U.S. Air Force photo/Michael Peterson)

Together, these reefs form a network of systematic resilience that, if adequately conserved, could form part of a strategy for maintaining the system as a whole. While the researchers estimate these reefs contribute to the resilience of nearly half the entire Great Barrier Reef, they make up only 3% of the total number of reefs in the system, pointing at the importance of ensuring effective local conservation to maintain these key populations. It’s also vital to improve conditions at the recipient locations, as water quality and other factors can affect the likelihood of larval settlement and healthy growth in these areas. The importance of these conservation measures will likely increase in the future as well, as climate change makes life harder for corals in both location types and the need for recolonization sources becomes more dire. Hock et. al. offer a method for prioritizing reef conservation and restoration that might maximize benefits while reducing cost. However, the researchers also make it clear that global action is still required to reduce the pressures that threaten all coral reefs. So now, we turn to you. Reducing your disposable plastics consumption, joining a beach cleanup, talking to your politicians – what will you do to help save our coral reefs?

Hock K, Wolff NH, Ortiz JC, Condie SA, Anthony KRN, Blackwell PG, et al. (2017) Connectivity and systemic resilience of the Great Barrier Reef. PLoS Biol 15(11): e2003355.

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