Coral reefs are vulnerable on multiple fronts:
Overfishing: Overfishing has caused a decline in populations of key reef species and negatively impact coral reef ecosystem structure, function, and economic value.
Destructive Fishing Methods: Destructive fishing methods – especially explosion of dynamite and poisoning with cyanide – are often used to stun reef fish so they can be captured for the aquarium and live food trades.
Contact with Boats, Anchors and Divers: Corals can be damaged or destroyed by shipwrecks, anchors and careless drivers
Coral Harvesting and Mining: Careless harvesting of coral for jewelry, aquarium use or other purposes can damage reefs.
Sewage: Human sewage discharged from coastal developments can cause diseases in corals, for example the White Pox disease.
Sedimentation and Pollution: Sediment from soil disturbance or erosion harms corals by decreasing light penetration into the water and reducing photosynthesis by algae. Excessive sediments can smother reefs. Chemical and nutrient runoff from coastal developments lowers water quality and can stimulate excessive growth of macro algae at the expense of corals, decreasing biodiversity
Sea Surface Temperature: Elevated sea surface temperatures cause coral bleaching and increased damage to reefs from breakage as storm frequency and intensity increase.
Ocean Acidification: Ocean acidification decreases the availability of calcium carbonate and the ability of corals to make and retain their exoskeletons.
Overfishing, destructive fishing practices, coral harvesting, mining, sewage, sedimentation, pollution, elevated sea surface temperatures and ocean acidification are all stressors. Less stress and greater resilience to stress increase the likelihood of coral reefs living beyond the Anthropocene. So saving the coral reefs is a two-part project: reducing stressors and increasing the ability to bounce back from stressors that are hard to reduce, such as stressors related to climate change, namely rising sea surface temperatures and ocean acidification.
To prevent major die-offs of coral, we will have to manage coral reef ecosystems. Such management may entail:
Banning gill nets and aquarium collecting
Limiting or prohibiting fishing of beneficial herbivores such parrotfish
In some areas, banning all fishing
Integrating coral reef management with land-use and coastal zone planning to reduce pollutants such as fertilizer run-off.
Practicing “bio-buffering”, such as growing sea grasses to absorb CO2 and reduce acidity in local waters.
Replanting bleaching-resistant coral
Enhancing enforcement of laws and regulations designed to protect reef ecosystems
And of course: more research is needed to develop ever-more resilient strains of coral and to perfect the technique of “microfragmentation”. This technique consists of breaking the corals into smaller pieces of 1 to 5 polyps, stimulating the coral tissue to grow and allowing them to grow into clones up to 50 times the normal growth rate. Microfragmentation may sound like science fiction, but it’s already been tried - with great success, as reported recently by Amy Wilson in Medium:
“Thanks to this technique, labs are able to fragment, grow and recombine corals in under 2 years to a size which would normally take 100 years, enabling much faster restoration of reefs. Furthermore, the recombined colonies become sexually mature, which would usually take up to 75 years. They have now successfully planted more than 20,000 corals onto depleted reefs in the Florida Keys.”
There is hope yet.
References and Links:
Chung, A., T. Oliver, et al. (2019). "Translating resilience-based management theory to practice for coral bleaching recovery in Hawai‘i." Marine Policy 99: 58-68. https://doi.org/10.1016/j.marpol.2018.10.013
Datta, R. & Sarkar, D. Bio-Buffering to Combat Ocean Acidification? Current Pollution Reports (2018) 4: 283. https://doi.org/10.1007/s40726-018-0101-0