Are Certain Coral Reefs More Resilient Than Others to Human Impact?

Check out this answer from Consensus:

The resilience of coral reefs to human impact is highly variable and influenced by a range of factors, including geographic location, local human activities, and ecological conditions. While some reefs in remote areas may not be as resilient as previously thought, certain reefs close to human populations have shown relative resilience. Understanding these variations is essential for developing targeted conservation strategies that can effectively protect and restore coral reef ecosystems.

Coral reefs are vital marine ecosystems that provide numerous ecological, economic, and social benefits. However, they are increasingly threatened by climate change and human activities. Understanding the resilience of different coral reefs to these stressors is crucial for effective conservation and management strategies. This article explores whether certain coral reefs exhibit greater resilience to human impact compared to others, drawing on recent research findings.

Variability in Coral Reef Resilience

Research indicates that the resilience of coral reefs to human impact varies significantly across different regions and conditions. For instance, a study on the coral reefs of the Comoros Archipelago in the Western Indian Ocean found high variability in reef condition and vulnerability. The live coral cover ranged from 6% to 60%, and fishery species biomass varied between 20 and 500 kg per hectare. Interestingly, offshore sites around the islets south of Mohéli were less impacted by negative pressures such as fishing, soil erosion, and river pollution, suggesting these reefs are relatively resilient to current anthropogenic stresses1.

The Role of Remoteness

Contrary to the common belief that remote coral reefs are more resilient due to their isolation from local stressors, recent findings challenge this notion. A study examining the relationship between local human influence and coral community resilience found no significant correlation between human influence and resistance to disturbance. Surprisingly, some areas with greater human development showed faster recovery from disturbances compared to their more isolated counterparts. This suggests that remoteness does not necessarily enhance coral reef resilience and that some reefs close to human populations may be relatively resilient2.

Geographic Disparities in Resilience

The resilience of coral reefs also appears to be influenced by geographic factors. Research focusing on the Caribbean region identified several factors that might predispose these reefs to low resilience, including faster rates of macroalgal growth, higher rates of algal recruitment, and lower herbivore biomass. These factors contribute to the Caribbean reefs’ susceptibility to coral-macroalgal phase shifts. In contrast, Indo-Pacific reefs would need to be heavily degraded to exhibit similar bistability or phase shifts, indicating a higher resilience in these regions3.

Are certain coral reefs more resilient than others to human impact?

Douglas Fenner has answered Near Certain

An expert from National Oceanic and Atmospheric Administration in Marine Biology

Yes, there is quite a bit of evidence that some corals are more resilient than others. There are two different things, the ability to withstand human impacts, and the ability to quickly recover. In general, species that reproduce well and grow fast can recover best, and some of the best at that are branching species, especially the staghorns (Acropora), cauliflower corals (Pocillopora) and branching fire corals (Millepora). In the Caribbean, the two Acropora species (staghorn and elkhorn) grow fast, however they don’t reproduce very much. They mostly reproduce asexually, by fragmentation. Indo-Pacific Acropora do both very well and are champions at recovery.

There is evidence that coral lifeforms, genera, species, and individual colonies vary in how affected they are by high temperatures and mass coral bleaching. Some branching corals are more affected than massive corals. Acropora, Pocillopora and Millepora have been reported as more sensitive to high temperatures, and massive Porites less. There are now a couple of studies that have found wide differences between individual species of several genera. So individualt species of Acropora vary between more sensitive and less sensitive, and the same for other genera. Individual colonies of the same species can vary a lot as well. I have pictures of colonies that at totally bleached white right next to colonies of the same species that aren’t bleached at all. I’ve even seen a few colonies that aren’t bleached when all other colonies next to them have been killed by bleaching.

Corals also differ greatly in their ability to survive sediment. Part of the differences are due to colony shape, colonies with steeply inclined surfaces tend to have the sediment slide off, while those that are flat or cup-shaped accumulate sediment which then kills them.

Corals also differ in what diseases they are subject to. The two Acropora in the Caribbean have lost 90-95% of their colonies which were killed by one disease, “white band.” But that disease does not attack other species. Each disease attacks a different range of coral species. One coral disease is caused by a bacterium that lives in vertebrate digestive systems, including humans, and so could possibly be spread in human sewage. Several diseases spread faster and damage or kill more corals at higher temperatures, and so human-caused global warming is increasing coral disease. The Caribbean has been hit hardest by coral diseases which have increased greatly in abundance in recent decades, which seems likely due to general human impacts that may reduce coral colonies’ ability to resist disease.

In the Indo-Pacific, crown-of-thorns starfish prefer to eat the tissues of some corals like Acropora over those of other corals like Porites. When they can’t find preferred corals to eat, they will eat the dispreferred types. There is good evidence that outbreaks of crown-of-thorns starfish outbreaks are more likely when there is nutrient runoff from land that fertilizes the growth of phytoplankton, which feeds starfish larvae so more survive and form outbreaks. Outbreaks can kill millions of corals and have been particularly destructive in Japan and on the Great Barrier Reef and continue to be on the latter.