Protective and vulnerable at the same time

Written by Carla Elliff

Climate change is one of the most pressing issues for marine environments. From sea level rise to ocean acidification, coral reefs have become a sort of poster-ecosystem for demonstrating the consequences of these changes.

That being said, it is quite surprising to think that coral reefs could actually help us respond to the impact of climate change. But how can something so vulnerable also provide us with protection? Nature-based climate change adaptation.

The idea that we can use nature to our advantage is in no way new. However, when we think of adapting our coastal communities to face climate change, we usually imagine armored shorelines and concrete walls protecting where people live.

For some time now, coral reefs have been studied to see how they can help.

Picture1
Figure 1: Waves crashing on the reef crest, away from the shoreline, promoting calm waters on the island of Boipeba, Brazil.

Waves

Before going in to how coral reefs protect our shorelines, let’s understand how a wave works.

Most waves are formed by wind blowing over the oceans, whipping water up into high crests and low troughs. When a wave reaches shallow waters, it begins to pile up and grow in height. At one point it becomes unstable and topples over. After the wave breaks, all that energy it was carrying dissipates until the water becomes calm again.

The problem here is that some waves are very strong and only break when they are close to the shoreline. That means there’s not enough time to dissipate all that energy, which instead causes erosion and destruction of coastal infrastructure.

With climate change causing more intense and more frequent storms, we can expect the service of shoreline protection to be even more important.

Shoreline protection by coral reefs

Because a reef is a sudden “bump” on the seafloor it forces waves to pile up and break. Depending on the distance of the coral reef from the shoreline and other factors, this may be enough to avoid strong waves from causing any damage to the shoreline.

 

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Figure 2: Schematic view of how a coral reef promotes shoreline protection (source: Elliff and Silva, 2017. doi: 10.1016/j.marenvres.2017.03.007)

But why not just build a breakwater? While these constructions have served their purpose in many places, they are not perfect. Coastal oceanography is very complex, so it is not uncommon that by installing a solution in one area, you are actually just transferring your problem elsewhere. This was observed in the state of Pernambuco, Brazil, for example. Two semi-submerged breakwaters were built to mitigate erosion on the coast of Olinda, but this intervention resulted in problems for other neighboring beaches.

Coral reefs and other natural habitats that provide shoreline protection, such as mangroves, also promote other important services: provision of food, recreation and tourism opportunities, carbon sinks etc.

By protecting reefs, we get a sort of “two for the price of one”: multiple benefits by conserving or restoring only one . Also, studies have shown that it is much more cost effective to invest in nature conservation and restoration to promote ecosystem services than to build and maintain artificial structures designed to do the same job.

Extra reading

If you’d like to read more about how coral reefs protect our shorelines, take a look at this article I published as part of my PhD project:

Carla I. Elliff & Iracema R. Silva (2017). Coral reefs as the first line of defense: Shoreline protection in face of climate change. https://doi.org/10.1016/j.marenvres.2017.03.007

If you are interested in how waves work, I would also recommend going to NOAA’s webpage:

https://oceanservice.noaa.gov/facts/wavesinocean.html

And, finally, if you are unsure how you can change your behavior to help fight climate change, check out this list of actions by the NRDC:

https://www.nrdc.org/stories/how-you-can-help-fight-climate-change

 

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