Over the course of the last several blogs, we have been focusing our attention primarily on the ways that climate change affects different types of fish species. In this blog, we will shift our attention to focusing on the ways that climate is affecting coral reefs. To begin, climate change has been identified as the biggest global threat to coral reef ecosystems. With rising temperatures due to climate change, coral bleaching and infectious disease outbreaks are becoming more common. In addition, calcification rates in reef-building and reef-associated organisms have already begun to fall as a result of carbon dioxide being absorbed into the oceans from the atmosphere. This process occurs through altering of seawater chemistry by decreasing the pH levels. The process is known as ocean acidification.
Some of the ways that climate change will affect coral reef ecosystems is through rising sea levels, changes to the intensity and frequency of tropical storms, and alterations in ocean circulation patterns. When these factors are combined, they drastically change the function of the ecosystem, along with the goods and services that the ecosystems provide to people around the world (National Ocean).
As we mentioned already coral bleaching is one of the threats to coral reefs. Coral bleaching occurs as a result of rising or falling water temperatures, which can create stress on coral polyps. This stress can cause them to lose algae that live in the polyps’ tissue. This algae provides the coral polyps with the food required for them to survive. The name “coral bleaching” comes from the fact that the coral turns completely white after the algae leaves it. While a coral is capable of surviving a coral bleaching event, it is under more stress and becomes more vulnerable to disease and other possible threats.
Another topic that has been mentioned is ocean acidification. The ocean absorbs about one-third of the excess carbon dioxide from the atmosphere, leading to a more acid in the ocean. A coral reef needs to produce limestone (calcium carbonate) in order for it to grow. This calcium carbonate must be produced at a rate greater than the rate at which the reef is being eroded. Ocean acidification slows the generation of calcium carbonate in coral reefs, and thus the growth of coral skeletons is slowed as well (Florida).
Another threat to the livelihood of coral reefs is the rises in sea levels that have resulted from the changing climate. Reef morphology which includes colony shape and size, cross-reef relief, surface rugosity, and so on. If all facets of reef morphology can remain on pace with rises in sea levels, then it is likely that any changes in depth-controlled process will miniscule or below the capability of detection. This; however, is not the case in Hawaii and parts of the Pacific where vertical reef accretion rates are lower than the predicted rate of sea level rise. With this in mind, it is unlikely that reefs in these locations, as well as, other will be able to keep pace. As a result of the inability to keep pace with rises in sea levels, some coral reefs will experience minute but important changes in selected physical processes.
Additionally, recent studies show that movement of submarine groundwater discharge from Hawaii and other High islands is notable. This water is also usually colder and more enriched by ocean-derived nutrients than the surrounding sea water. Ecosystem functions of submarine groundwater to coral reef ecosystems can be hypothesized to (1) cushion thermal stress (bleaching) in corals that are experiencing warming, and (2) provide nutrients to otherwise oligotrophic coastal waters. While an excess of the latter has caused complete phase shifts through loss of coral and replacement by macroalgae, the role of the former has not yet been tested. Both factors of the hypothesis may be substantially altered by future climate change and proposed land use that change groundwater quality, quantity, flux, composition, and fate, particularly in quickly developing areas. (Pacific)
The last factor that we will discuss is the way climate change reduces coral reefs’ ability to protect coasts. Coral reefs, which are under pressure from human activity and climate change, may have a limited ability to protect tropical islands wave attack, erosion and salinization of drinking water, which aids in maintaining life on these islands. New research by Dutch independent institute for applied research Deltares and the U.S. Geological Survey gives guidance to coastal manager on how to assess the ways that climate change will affect the ability for coral reefs to mitigate coastal hazards.
Presently, some low-lying islands experience flooding related to wave events a few times per decade. The rate of flooding is predicted to increase as sea levels rise and coral reefs decay. The dead coral are smoother and do not stop wave energy as easily. A loss of coral cover not only increases shoreline erosion, but also affects the drinking water resources on the islands. Coastal managers need to know the extent of protective coral cover that their reef system will lose, so they can take the proper action to help mitigate the resulting impacts. The new study helps provide guidance on the sensitivity of a local reef. The results implied that coast fronts with narrow reefs and steep faces and smoother, deeper flats can expect to see the highest wave rump, and thus a greater potential for island flooding. An increase in wave rumps for high water levels (which are expected with sea level rise), higher waves, and lower bed roughness (as corals become smoother from degrading) are all effects that can be expected due to climate change. As a result of the topics just discussed, rising sea levels and climate change will have a substantial negative impact on coral reefs’ ability to mitigate future effects of hazards (USGS).
Florida Keys National Marine Sanctuaries. National Marine Sanctuary. National Oceanic and Atmospheric Administration. Coral bleaching and ocean acidification are two climate-related impacts to coral reefs. https://floridakeys.noaa.gov/corals/climatethreat.html Web. April 13, 2022.
National Ocean Service. National Oceanic and Atmospheric Administration. U.S. Department of Commerce. How does climate change affect coral reefs? https://oceanservice.noaa.gov/facts/coralreef-climate.html. Web. April 13, 2022.
Pacific Coastal Marine Science Center. Sea-Level Rise and climate Change impacts to reefs. https://www.usgs.gov/centers/pcmsc/science/sea-level-rise-and-climate-change-impacts-reefs August 10, 2020. Web. April 14, 2022.
USGS – Science for a Changing World. Climate Change Reduces a Coral Reefs’ Ability to Protect Coasts. https://www.usgs.gov/news/national-news-release/climate-change-reduces-coral-reefs-ability-protect-coasts. July 22, 2015, Web. April 14, 2022.
https://www.youtube.com/watch?v=WRGQGRy2wJ0. YouTube. Video. NOAA Coral Reef Conservation Program. Retrieved April 14, 2022.
https://d9-wret.s3.us-west-2.amazonaws.com/assets/palladium/production/s3fs-public/styles/side_image/public/thumbnails/image/SLR_sedflux_restime_plot_R-2.jpg?itok=kUqPv6Nf. Image. Retrieved April 14, 2022.