Climate Change and Coral Reefs
September 22nd’s Science magazine contains an editorial titled “Refilling the coral reef glass.” The author is Dr. David Obura, chair of the International Union for Conservation of Nature’s Coral Specialist Group. The editorial discusses the impacts of climate change on coral reefs worldwide. Dr. Obura stresses the need for countries to implement policies to reduce/remove waste (i.e. carbon dioxide). This is needed in order to stabilize global temperatures. If this is not accomplished, he states that “it is virtually certain that major reef systems will not survive in the Anthropocene.”
The term Anthropocene was first proposed almost two decades ago. It describes the era in which the global environment has been shaped by human kind. While it has not been added to the official Geologic Time Scale, the term is widely used. It is often used in connection with global climate change.
So how is climate change impacting coral reefs? For about the past 30 years, coral scientists have noticed an increasing frequency of coral bleaching. Corals are animals that have a unique partnership with microscopic algae. These algae are found inside the animal cells. Their golden-brown color contributes to the yellow-brown coloration of most reef corals. When corals are stressed, something happens to cause this partnership to break down. The algae are lost from the coral, and the corals then appear white. Without the algae, the thin veneer of living coral tissue is transparent, This allows the white limestone coral skeleton to be seen. Temperature is the best-known stressor of corals. An increase in summer water temperatures of only one or two degrees Celsius (for a period of a few weeks) can trigger coral bleaching.
A partially-bleached brain coral. Photo credit: NOAA
In the time period from 1880-2012, global land and sea temperatures increased by an average of 0.85 degrees Celsius. While this may not seem like a large change, for corals, it could be enough to trigger more frequent bleaching. Corals sometimes recover from bleaching events once the stressor goes away. However, they are more vulnerable to disease or other additional stressors during this time.
Scientists in many coral reef areas, including Florida, are growing corals in nurseries. These corals are used to restore damaged reefs. In some cases, corals that are naturally growing in warmer water areas are being used to produce more corals that will hopefully be more tolerant of warming water temperatures (and less prone to bleaching).
Staghorn corals being grown in a coral nursery. Photo credit: FWC
As we well know, the 2017 hurricane season has been devastating for many areas. The 2014 National Climate Assessment states, “The intensity, frequency, and duration of North Atlantic hurricanes, as well as the frequency of the strongest (Category 4 and 5) hurricanes, have all increased since the early 1980s. Hurricane-associated storm intensity and rainfall rates are projected to increase as the climate continues to warm.”
Impacts of Hurricanes Irma and Maria
Researchers have not yet been able to fully assess the impact of the recent storms on coral reefs and nurseries. Initial observations from the Florida Keys show that while Irma had some impact on coral nurseries there (relocating some of the corals as far north as Fort Lauderdale!), many of the young corals were relatively unscathed. The story from Puerto Rico is less optimistic. Dr. Edwin Delgado is a researcher at the University of Puerto Rico’s Center for Applied Tropical Ecology and Conservation. He reports that that island’s coral restoration efforts suffered a huge setback. “We did lose 95-99% of our coral farms and 100% of our coral out-plants with 7-11 meter high swells during Irma in Culebra. We lost 15 years of work, and close to 60,000 corals. Now with Maria I think we lost everything else.”
Time will tell whether coral reefs are able to survive “in the Anthropocene.”