Written By Ayla Sage
Edited Sara Gagliardi
Have you ever thought about what it’d be like to live life underwater? Well, that might be the case in the next 50 years or so if you live in a coastal city or town, like Miami. OK… you might not actually be underwater but coastal flooding and erosion are some serious problems that need to be taken into consideration as coastal populations continue to grow and the effects of climate change intensify.
How Coral Reefs Protect the Shoreline
Although coral reefs are in the ocean, they play a major role in protecting our terrestrial shorelines. By definition, submerged breakwaters are structures that are designed to reduce incident wave energy . They can come in various shapes and sizes, but ultimately they are all made with the goal to protect our coasts from erosion or port channels from sand deposition. Luckily, coral reefs act as natural, low-crested, submerged breakwater systems. As waves pass over the topographical coral reefs, the frictional interaction between the water molecules and rigid coral structures decreases the overall incident energy of the wave. This becomes especially important in cases of high intensity storms. These reefs provide significant annual expected benefits for flood protection. Across reef coastlines, reefs reduce the annual expected damages from storms by more than $4 billion ! Without them, annual damages would increase by more than double (118%) . So, everyone give a big thank you to coral reefs for not making our taxes go up!
Climate Change Consequences
Over recent years, reefs have experienced significant global losses in live coral cover and reef structure. These losses can be attributed to activities such as coastal development, sand and coral mining, overfishing, storms, and climate-related bleaching events . As corals die, other microbial organisms take over and begin the process of bioerosion and dissolution of the underlying reef calcium carbonate (CaCO3) structures . Essentially when the coral skeletons become exposed from tissue loss induced by heatwave-induced mortality events, they become encased with a complex biofilm of phototrophic microbes. The metabolic activity of the microbes accelerates CaCO3— what coral skeletons are made out of – dissolution at rates that exceed CaCO3 accretion rates of healthy growing corals . Overall, the dissolution reduces skeletal density and hardness while increasing porosity. This causes the entire reef community to lose shape and structure as more colonies fall to their doom- transitioning from reefs to rubble.
To make matters worse, sea levels are continuing to rise, which impacts our coastal communities, and these impacts are magnified as reefs are diminishing. The scientific community commonly uses statistical analyses to analyze intense storm events. These analyses allow them to prepare for worst case scenarios and to implement preventative measures. When scientists ran a model, they found that in the year 2100, the land being flooded would increase by 64% compared to if the storm were to occur present day . This model assumes that emissions affecting climate change will continue to be high, which they most likely will be since humans are struggling to get the issue under control. Even worse, if relative sea level rise is coupled with a 1 m loss in reef height like figure 1 shows, the land being flooded increases by 116% . Like I said, we might not be completely underwater, but many of us will probably be standing knee-deep.
Hybrid Coral Reefs for the Future
Alright, by now this might sound a tad worrisome, especially if you live by the water – but don’t freak out just yet! Engineers and ecologists have been working in collaboration to create new designs of submerged breakwater structures. These structures are sometimes called hybrid artificial reefs because they not only work to dissipate the wave energy, but also restore degraded reef sites and enhance biodiversity. It’s not enough to be designing artificial reefs solely to maximize coastal defense in the absence of corals. Active reef growth is essential to keep pace with sea level rise and to provide new sediment to beaches. Fun fact: more than 80% of sand on beaches around tropical coral reefs comes from parrotfish poop! These parrotfish take bites out of chunks of corals, including the calcium carbonate skeletons, digest it, and release it back as fine sediment a.k.a. sand .
At the University of Miami (UM), a team has been designing and testing different submerged breakwater systems. One of their most recent systems is composed of a bottom trapezoidal structure that will have live corals placed on top. For now, they are running test with dead coral skeletons, but when implemented, the top will be covered with live Acroporiid corals . So far what they have found from running tests in UM’s wave tank simulator is that the trapezoidal structure reduces wave energy by up to 63%, but when coral skeletons were added on top an additional 14% of wave energy was mitigated .
Through conservation, outreach and education of our coral reefs, we hope that it becomes a common understanding that corals are in peril. While the end goal is still for humans to reduce greenhouse gas emissions, I believe it’s important to show how we are mitigating our impacts and taking greener approaches. Although there is still much to be done, I hope the message here inspires, educates, and encourages others to put forth their best effort to make conscientious decisions going forward, creating more environmentally friendly lifestyles! If you are curious about finding ways to contribute and help, it’s a good idea to begin with your local community. Look for local environmental organizations and programs and ask if they have any volunteer opportunities. Every contribution helps in fighting these global problems.
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 US Department of Commerce, National Oceanic and Atmospheric Administration. (2017, August 14). How Does Sand Form? NOAA’s National Ocean Service. https://oceanservice.noaa.gov/facts/sand.html.
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 Beck, M. (2019, May 7). Coral reefs provide flood protection worth $1.8 billion every year – it’s time to protect them. The Conversation. https://theconversation.com/coral-reefs-provide-flood-protection-worth-1-8-billion-every-year-its-time-to-protect-them-116636