Coral reef degradation in Hawaii, USA

Problems

• Rising water temperatures

  Coral reefs in Hawai’i are home to spectacular biodiversity of plant and animal species (many endemic to the Hawaiian archipelago), support a deep-rooted culture of subsistence fishing, provide coastal protection, and are central to tourism and recreational activities. 
  
  Rising water temperatures cause coral reef degradation in Hawaii by affecting the health and survival of corals and their symbiotic algae. Corals live in a mutualistic relationship with microscopic algae called zooxanthellae, which live inside their tissues and provide them with food and oxygen. When water temperatures become too high, corals can expel their algae, losing their color and energy source. Bleached corals are not dead but more vulnerable to disease, predation, and mortality.
  
  The 2019 El Niño marked a significant occurrence of widespread coral bleaching in Hawai’i due to record-breaking heat and the arrival of the massive ocean heatwave known as “the Blob.” With the ongoing effects of climate change, scientists predict an increase in the frequency and intensity of El Niño events attributed to more frequent and warmer sea surface temperatures (SSTs).
  
  According to a study by the National Institute of Food and Agriculture, Hawaii experienced extreme coral bleaching events in 2014 and 2015, which affected more than 50% of coral reefs across the archipelago. The study also found that human activities and natural events can slow down reef recovery after bleaching by increasing stress and damage to corals. For example, tourism, fishing, sedimentation, and nutrient pollution can reduce coral resilience and diversity.
  
  Another consequence of rising water temperatures is ocean acidification, which is the decrease in the pH of seawater due to the absorption of carbon dioxide from the atmosphere. Ocean acidification can affect coral growth and calcification, which is building their skeletons from calcium carbonate. Acidic water can dissolve calcium carbonate, making it harder for corals to maintain their structures and repair damage.
  
  Rising water temperatures and ocean acidification are global threats to coral reefs that are worsened by climate change. They can negatively impact the biodiversity, ecosystem services, and cultural values of coral reefs in Hawaii and worldwide.

• Overtourism

  Millions of tourists visit Hawaii yearly, but tragically, these tourists are damaging and destroying these islands’ natural environment, particularly its coral reefs. 
  
   According to a study by Arizona State University and Princeton University, there is a strong correlation between the number of tourists visiting a reef site and the decline in coral cover and diversity. The study used high-resolution aerial mapping and geotag data from Instagram to measure the impact of tourism on coral reefs across the Hawaiian archipelago. The researchers found that tourism can harm coral reefs by increasing physical damage, sedimentation, nutrient input, and disease transmission. 
  
  The data also showed that most visitors either stayed close to shore or remained on the beaches, whilst a smaller (but not insignificant) number of tourists went snorkelling or took scuba diving excursions that brought them into indirect and direct contact with more distant reefs. These interactions were obvious from the condition of the corals — the farther that the corals were from shore (and from the hoards of people), the better their health.