Threats to Coral Reefs

Context: Recent studies and reports have warned about severity of coral bleaching events, and the impact it has on coral reef ecosystems.

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Key Highlights of the Study

• Vulnerability to environmental changes: Corals are highly susceptible to bleaching when the water temperature rises beyond a certain point. This vulnerability is a result of global warming and the increasing temperatures experienced worldwide.
• Appearance-based definition: When corals bleach, they lose their vibrant colors and turn white. This change in colour serves as a visible indicator that something has changed in the surrounding water, making it valuable for observers to recognize and assess the health of coral reefs.
• Causes of zooxanthellae expulsion: When the ocean environment undergoes changes such as excessive temperature increase, acidity, or increased brightness, the zooxanthellae living within the coral leave. As a result, the coral loses its colour and appears bleached.
  • Corals have a symbiotic relationship with algae called zooxanthellae.
  • The zooxanthellae provide essential nutrients such as amino acids and sugars to the corals, while receiving minerals and carbon dioxide in return.

• Additional stressors: Besides temperature, other stressors like low tides, water pollution, and ecosystem changes resulting from the climate crisis can further impact the health of corals and increase their susceptibility to bleaching.
• Survival and recovery: While coral bleaching can be detrimental and even fatal for many coral colonies, some have shown the ability to survive and recover from bleaching events.
  • Example: Japan’s Iriomote Island experienced bleaching in 2016 but displayed signs of recovery by 2020, indicating the potential for resilience and restoration in certain coral populations.

Global Warming and Threats to Coral Reef

Global warming poses a more significant threat to coral growth and reef accretion than ocean acidification.

• Ocean acidification (OA) as a threat to coral reefs:  OA is the gradual decrease in the pH of the Earth’s oceans due to the uptake of carbon dioxide (CO2) from the atmosphere.
  • Reduced calcification: The lower pH of ocean water affects the growth and survival of coral reefs by reducing calcification rates in reef-building organisms i.e. coral polyps.
  • Affects coral reproduction: Coral reefs reproduce by spawning eggs and sperm into the water. When the water is more acidic, the development and survival of coral larvae may be affected.
• Global warming as a threat to coral reefs: The study has found that coral reefs are more affected by global warming-related heat-stress than by ocean acidification.
  • The study also found that the effects of temperature on the metabolism of corals were stronger than the effects of increased CO2.
  • Coral bleaching: As global warming continues, the frequency and severity of bleaching events will increase, making it harder for coral reefs to recover from these disturbances.

Case Study: 2016 & 2017 Mass coral bleaching in the Great Barrier Reef

• The Great Barrier Reef, located off the coast of Australia, is the largest coral reef system in the world.
• In 2016 and 2017, the Great Barrier Reef experienced mass bleaching events, which were caused by a combination of high ocean temperatures and El Niño.

• Both the events collectively affected almost two thirds of the Great Barrier Reef.
  • Disease outbreaks: High temperatures can also increase the incidence and severity of coral diseases.
  • Changes in storm patterns: This leads to stronger and more frequent storms that can cause the destruction of coral reefs.
  • Sea level rise: may lead to increases in sedimentation for reefs located near land-based sources of sediment. Sedimentation runoff can lead to the smothering of coral.
  • Reduced growth and reproduction: Increased water temperatures can also negatively affect the growth and reproduction of coral reefs.
  • Changes in coral community composition: High temperatures can cause certain coral species to become more dominant or extinct, altering the composition of coral communities.

About Coral Reefs

• Coral reefs are diverse underwater ecosystems formed primarily by the accumulation of calcium carbonate exoskeletons secreted by corals.
• They are often referred to as the “rainforests of the seas” due to their rich biodiversity and importance in supporting a wide range of marine life.
• Coral reefs provide habitats, breeding grounds, and food sources for countless species, making them crucial for the overall health of ocean ecosystems.

Types

There are two main types of coral reefs:

• Fringing Reefs:
  • Fringing reefs are located close to the shorelines of continents or islands.
  • They develop directly from the coastline, and their shallow, nearshore environments make them easily accessible.
  • Fringing reefs typically grow parallel to the shorelines, forming a border or fringe along the coastline.
• Barrier Reefs:
  • Barrier reefs are found farther offshore, separated from the mainland by a lagoon or deep water.
  • These reefs are characterized by a continuous and extensive reef structure parallel to the coastline, forming a barrier between the open ocean and the shoreline.
  • Barrier reefs can be quite large, with the Great Barrier Reef in Australia being the most famous and largest example.
• Atoll:
  • There is another type of coral reef called an “atoll,” which is a circular or oval-shaped reef that surrounds a central lagoon.
  • Atolls are typically found in the open ocean, often formed on the remnants of submerged volcanic islands.

Coral Bleaching and Consequences

• Coral bleaching is a phenomenon where corals expel the symbiotic algae-zooxanthellae from their tissues due to stress caused by changes in environmental conditions such as elevated sea temperatures, increased solar radiation, ocean acidification, infectious diseases, chemical pollution, increased sedimentation, and human-induced threats.
• When the zooxanthellae are expelled, the corals lose their colourful appearance and turn completely white, revealing the translucent tissues of calcium carbonate.

The consequences of coral bleaching include

• Disruption of the food chain: Changes in coral communities can impact species that depend on them, such as fish and invertebrates that rely on corals for food and shelter. This can disrupt the entire food chain in coral reef ecosystems.
• Loss of biodiversity: When corals die due to bleaching, genetic and species diversity decline, leading to a loss of biodiversity within coral reef ecosystems.
• Economic impact: Healthy coral reefs are important attractions for tourism, including activities like diving. Bleached and degraded reefs can deter tourists, negatively affecting local economies that depend on reef-based tourism.
• Food availability: Coral bleaching can cause significant shifts in fish communities, resulting in reduced catches for fishers. This can have implications for the availability of seafood and impact the livelihoods of communities dependent on fishing.
• Coastal protection: Coral reefs serve as natural barriers, absorbing wave energy and protecting coastlines from erosion, storm damage, and flooding. The loss of healthy coral reefs due to bleaching can leave coastal communities more vulnerable to these natural hazards.

Threats to coral reefs other than ocean acidification and global warming

• Pollution: Pollution from sources such as agricultural runoff, sewage, and industrial discharges can damage coral reefs by smothering them with sediment, increasing the growth of harmful algae, and reducing the water’s oxygen levels.
• Overfishing: Overfishing can disrupt the balance of coral reef ecosystems by removing key herbivores and predators.
• Coastal development: Coastal development can damage coral reefs by destroying their habitats and increasing the amount of sediment and pollution in the water.
• Unsustainable tourism: Overuse of coral reefs for tourism and recreation can lead to physical damage to the coral, sedimentation, pollution, and overfishing.
• Invasive species: Invasive species such as the crown-of-thorns starfish and the lionfish can damage coral reefs by eating coral and competing with native species.

Stats IQ: Current scenario of degradation of coral reefs

• In 2019, the Global Coral Reef Monitoring Network (GCRMN) reported that coral reefs have declined by 50% in the last 30 years and it is expected that, this rate of decline could reach 70% by 2030.

Methods to protect and restore coral reefs

Major Initiatives

Several initiatives and programs that aim to protect and conserve coral reefs include:

• International Coral Reef Initiative (ICRI): ICRI is a partnership between governments, international organizations, and non-governmental organizations (NGOs) that aims to promote the sustainable management and conservation of coral reefs worldwide. It provides a platform for collaboration, knowledge exchange, and policy development.
• Global Coral Reef Monitoring Network (GCRMN): GCRMN is a network supported by the United Nations Environment Programme (UNEP) and other partners. It coordinates global monitoring efforts to assess the status and trends of coral reefs, facilitating data sharing and providing scientific information for conservation decision-making.
• Global Coral Reef Alliance (GCRA): GCRA is an international organization focused on coral reef restoration, research, and education. It works to develop and implement innovative techniques to restore damaged coral reefs and promotes sustainable management practices.
• The Global Coral Reef R&D Accelerator Platform: This platform aims to accelerate the development and implementation of cutting-edge science and technology solutions to address the threats facing coral reefs. It fosters collaboration between scientists, policymakers, and innovators to drive innovation and action for reef conservation.
• National Coastal Mission Program: In the case of India, the National Coastal Mission Program is an initiative aimed at protecting and sustaining coral reefs in the country. This program focuses on the conservation of coastal and marine ecosystems, including coral reefs, through various strategies such as research, awareness campaigns, and community engagement.
• Local and regional conservation efforts: Many countries and communities have implemented their own conservation initiatives, including the establishment of marine protected areas (MPAs) and the adoption of sustainable fishing practices.

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