Coral Reefs Key Hazards


Unfortunately for Hawaii, coral reefs are one of the most exposed ecosystems to climate change. Some species can migrate to more suitable living conditions, whereas coral cannot adapt to warming acidic ocean temperatures because they have no migratory capabilities. While the future for coral reefs looks grim, their only chance at survival is of human origin. Key hazards to the reef include:

  • An increase in oceanic water absorbing carbon dioxide causing corals to become stressed and bleach ( IPCC, 2014; NOAA, 2020; University of Hawaii, 2021; IPCC, 2022).
  • Watershed pollutants entering the ocean damaging corals (Cortés and Risk, 1985; Storlazzi et al. 2009; Fabricius, 2011; Tarya et al., 2018; Jones et al., 2020).
  • Overfishing causing less fish to graze on the coral disrupting the delicate balance of the reef (Health of U.S. Coral Reef Ecosystems, 2001; Fossa et al. 2002; Friedlander et al. 2017; EPA, 2020).


Hawaii state map and its location in the Pacific Ocean

n.a, 2015

Ocean Acidification Hazard

The burning of fossil fuels is occurring at a rapid rate increasing carbon dioxide (CO2) levels in the atmosphere (Steffan et al., 2018). With an uptake of carbon dioxide, the ocean absorbs more CO2 in the water, making it more acidic (Doney et al., 2019; Gattuso & Hansson, 2011). An increase in global surface temperature of 0.1 ℃, ensuring is a 50% likelihood of warming exceeding 1.5℃ in the near future with a low emissions scenario (IPCC, 2022). Atmospheric CO2 via anthropogenic sources has increased, affecting the coral reefs strict limit of 1.5℃ of warming (IPCC, 2022). Reaching 1.5℃ of warming would create irreversible damage as coral cannot adapt to global warming at the rate it is increasing (IPCC, 2022). The IPCC projects that 70-90% of coral reefs will die even with a 1.5℃ warming scenario (IPCC, 2022). Warming is expected to be most severe at mid-latitudes which is where coral reefs ideal habitat exists (IPCC, 2022). A very high confidence scenario is predicted that coral reefs are gravely threatened due to anthropogenic climate change (USGCRP, 2018).  

"1.5℃ of warming would create irreversible damage to corals"

CO2 levels in Hawaii and its affect on the pH of the ocean

NOAA; Lueker et al., 2000

Ocean Acidification Exposure and Vulnerability

Hawaii, surrounded by reef systems, experiences significant impacts of ocean acidification (Eversole & Andrews, 2014; USGCRP, 2018).

  • Recent expansion in acidity of the water surrounding the islands (Markel, n.d.).
  • The University of Hawaii monitors the concentrations of carbonate ions in the water
    • 20% decrease of carbonate ions making the water more acidic (2021).
    • 50% of the reefs died in certain areas because of increased ocean temperatures (Division of Aquatic resources, 2016). 

With the consistent uptake of CO2 in the atmosphere more CO2 is being absorbed into the oceans, causing Hawaii to have a large vulnerability to ocean acidification (Doney et al., 2019). 


The left shows a normal reef while the right shows a bleached reef.

Ove Hoegh-Guldberg, Global Change Institute, University of Queensland  

Adaptation and Resilience to Ocean Acidification

An adaptation to ocean acidification is the reduction of one's carbon footprint. However, the future for coral reefs is not bright considering that people are not decreasing their carbon footprint. Evidenced today with gas prices reaching six dollars, society continues to pay the steep price. The problem of emissions is an issue that needs consistent change and wherewithal to tackle. Society does not have the commitment to ward off such a significant stressor. It is not looking promising for coral reefs and coastal communities dependent on them. There has been some progress in coral gardening where damaged reefs are restored (Bartlett, 2017). Challenges faced to this are heat and acidity of the water where the coral is being restored (Bartlett, 2017).


Researchers investigating recent coral bleaching events off the coast of Lanai.

NOAA Sanctuaries, 2015

Hazard of Changing Watersheds

Coral covered in sediment 

University of Hawaii Coral Reefs, 2021

 Degradation of coral reefs have been seen in great volume due to pollution from land-based runoff (Stock, 2011).

  • Reefs can be exposed to sediments originating from sewage, nutrients, freshwater, and oil (Fabricius, 2011)
    • These stressors can exist for years because the sediments continue to be suspended in the water column (Fabricius, 2011).
  • Terrigenous sediments can either continue suspended in water, shrinking the light reefs needed for photosynthesis, or conceal the coral (Jones et al., 2020).
  • Smaller sediments blanket the coral making it more susceptible to trace metals, pesticides, and dissolved material bleaching them (Jones et al., 2020).

Exposure and Vulnerability of Changing Watersheds

Coral reefs in Hawaii experience watershed pollution from increased runoff and land erosion (Storlazzi et al., n.d.; Stock, 2011; NOAA, 2020).

  • Hawaii’s watersheds have been altered due to agriculture, invasive species, and wildfires (Watson, 2002).
    • Erosion, hence, became more prevalent as less flora created greater vulnerability to soils during intense rainfall (Stock, 2011).
  • The nitrate concentrations in the water off the Hawaiian coast are 50 times greater than what is considered normal (USGS, 2018).
    • Increased runoff from land-based contaminants contributes to the destruction of the coral reef ecosystem on the coast at a rapid rate compared to the projections of ocean acidification (USGS, 2018).
  • Hawaii is vulnerable to watershed erosion which contaminates the reef
    • Increased periods of drought followed by heavy rainfall cause large erosion events as dried material is washed to the oceans (Hawaii Climate Change Department, 2014).
    • Agriculture causes harmful runoff from the farms smothering the coral with toxic chemicals (pesticides) or sediment (Hawaii Archipelago, 2018).

(Photo: USGS, 2022)

Adaptation and Resilience to Changing Watershed Erosion

Coral is smothered with sediment off the coast of Oahu.

 Subramanian, 2017

According to NOAA, 2016:

  • Land management is crucial in decreasing the amount of erosion into the oceans.
  • Restoring the habit and cleaning up the damaged trees would allow for less erosion.
  • Stopping soil erosion prevent the reefs from being smothered by sediment.
  • Educating homeowners about issues of sedimentation has been proven effective.
  • Containing sediment with vegetation help with erosion prevention. 

Overfishing Hazard

The hazard of overfishing in coastal communities causes less fish to graze the reefs and decreases the coral's biodiversity (Health of U.S. Coral Reef Ecosystems, 2001; Fossa et al. 2002; Friedlander et al. 2017; EPA, 2020).

  • A healthy sustainable fishery promotes many activities such as commercial fishing, tourism, and food (NOAA, 2018).
  • Overfishing affects the structure of food-webs as there is less fish to graze that clean coral and keep algae from overgrowing (EPA, 2020).
  • Species that populate coral reefs, such as sharks, groupers, snappers, and mollusks are deemed of high value to fishermen (NOAA, 2002).
    • Overfishing of these species has been identified on virtually every U.S. reef inshore by islands that had substantial residents (NOAA, 2002).

(Photo: Reef Builders, 2021)

Overfishing Exposure and Vulnerability

Hawaii has seen a large decline in the health of its fisheries due to overfishing (Friedlander & Donovan, n.d.). In Hawaii, fish are victim to sustenance, commercial, and tourist fisherman (Friedlander & Donovan, n.d.). Juxtaposing the ideal research species from the highly populated main Hawaiian Islands (MHI) and the non-populated North-West Hawaiian Islands (NWHI) showed that in the MHI, 40 percent of the species had biomass under 25 percent of the NWHI numbers (Friedlander et al. 2017). These figures represent the health of the waters in non-remote (MHI) versus remote Hawaii (NWHI). Remote Hawaii (NWHI) clearly had increased health of ecosystems as there was less, if any, overfishing which allows for a productive reef that creates an abundant amount of aquatic life (Friedlander et al. 2017).


Fishes grazing the coral

StockVault, n.d.

Overfishing Adaption and Resilience

A turtle swimming above the reef.

Emma Reynolds

The problem of overfishing has positive solutions through regulations. Licenses requiring people to fish, certain species that are prohibited from fishing, and Marine Protected Areas (MPA)/Marine Life Conservation Districts (MLCDs) would ensure the safety of coral reefs from overfishing (Friedlander et al. 2017). Marine Protected Areas have been shown to increase biodiversity and quality of species mass/richness than in non-protected areas (Friedlander et al. 2017). . In MLCDs the biomass of fish was 2.6 times more extensive than adjacent non MLCD areas (Friedlander et al. 2017). Regulations on the fishing industry in Hawaii have proved to increase the diversity of reef dwelling species ensuring the viability of coral reefs in Hawaii.

Hawaiians Connection to Coral

A traditional outrigger canoe off the coast of Hawaii

Uhl, 1976

Local Hawaiians are not only losing the valued coral reefs but also must deal with witnessing an important symbol of their culture vanishing (NOAA, 2018). A Hawaiian creation chant during the first Kumulipo epoch signified the importance of corals in Hawaiian culture saying that coral was the first form of life (NOAA, 2018). This connection to life is continued today as people rely on the reefs for their livelihood​. A cultural connection is ever present amidst communities that depend on and protect native reefs (USGCRP 2018). Ancient Polynesians in Hawaii noted the frequent activities dependent on the sea such as fishing and swimming, which they became experts in (Coan, 1901). The Polynesian lifestyle was one that placed a heavy importance on seagoing adventures (Grayzel, 2019). If the ocean continues to acidify at the current rate, Hawaiians will lose the relationship to their ancestors as they cannot partake in the sea activities as their ancestors did. 




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