Coral reefs are an integral part of the ocean. These ecosystems only occupy 0.01% on the ocean floor. However, 25% marine life depends on them, and they provide vital habitat for many fish species and invertebrate types. They also have a huge impact on coastal communities with one million people benefiting. They provide food, livelihoods and reduce storm surge risk to coastal areas across the tropics. They also protect against erosion.
Coral reefs are important, but they face many threats, including nutrient runoff, deforestation and climate change. If coral reefs are not protected and restored immediately, they may cease to be a source of essential goods and services for communities around the world. These issues can only be addressed if we understand what coral reefs are and the relevant trends, threats, and reasons to be optimistic about the future of these amazing ecosystems.
Answering common coral queries
It can be difficult to understand the intricacies of coral reefs. This is a deep dive into the coral reefs, their threats and current status.
What is coral reef?
Coral reefs are three-dimensional, vast structures made up of coral animal colonies. These coral animal colonies secrete calcium carbonate, also called limestone. These limestone secretions accumulate over time and form structures that can be seen from space. There are 800 species of hard corals that build reefs. These coral colonies can take many forms and sizes. These coral colonies form vibrant underwater cities that host many invertebrate and more than 4,000 fish species.
The body of a coral animal (or “polyp”) is simple and transparent. It has a tubular body that’s covered with stinging tentacles. Although they have a central stomach that filters food, 95% of their nutrition comes via microscopic algae in the tissues of polyps, also known as “zooxanthellae”. Zooxanthellae produce sugars from photosynthesizing, which is what the coral animal needs for energy. This algae is also responsible for coral reefs’ famously vibrant colors.
What are the biggest threats to coral reefs
Both local threats and global threats to coral reefs include overfishing, sediment, nutrient, and marine pollution, and increasing ocean temperature and acidification.
Coral reefs are most at risk from overfishing. Overfishing can cause a shift in the ecology of the reef by removing herbivorous species that eat coral macroalgae. A major threat is sedimentation due to land clearing. The sediments in the water column can bury corals and reduce sunlight reaching the zooxanthellae. This will limit their ability to absorb nutrients from photosynthesis. In addition, algal cover can be affected by nutrient pollution caused by agriculture and sewage. Ships can cause damage to reefs by introducing invasive species or releasing pollutants.
Ocean warming is a growing threat globally due to climate change. Corals’ zooxanthellae are sensitive to temperature changes. Ocean warming can cause corals to lose their colored algae, a process called “coral bleaching.” The corals will appear with a bright white skeleton which deprives them of an important source for nutrition. If the corals don’t receive the symbiotic alga, or if they are unable to recover from bleaching, then eventually they will die.
Ocean acidity is also being caused by increasing levels of carbon dioxide in the seawater. This causes a decrease in the availability of aragonite which corals require to build their skeletons. The lack of aragonite can slow down coral growth, resulting in weaker coral structures that are more susceptible to erosion and damage. The trend in aragonite saturation has been decreasing over the past century. Current CO2 emissions are expected to keep this trend going into the next century.
What are the current conditions of coral reefs around the globe?
There is no single answer to the question of how coral reefs are doing. There are many factors that affect the state of coral reefs around the world. Some have been saved. Most of the reports are grim. Nearly half the world’s coral reefs have been affected by climate change, overfishing and pollution. In some areas, hard coral cover has dropped significantly, and there has been a change in coral community structure with loss of vulnerable coral species and loss of diversity .
The Global Coral Reef Monitoring Network has released a report that provides a more detailed chronology of coral loss. This report uses data from 35,000 coral survey surveys in 73 countries, covering the last 40 years. It reflects fluctuation in algal cover and live hard coral cover, which are key indicators of coral reef health. The findings, although limited in data, suggest that the average live hard coral coverage was fairly stable before the 1998 mass coral bleaching. The global coral loss was 8%, but coral reefs rebounded over the next decade.
Between 2009 and 2018, coral coverage declined by 14%. This was primarily due to repeated large-scale coral bleaching episodes and insufficient time between events for corals to recover. Coral decline is also caused by local disturbances and threats. They hinder coral bleaching recovery and create an environment for algae to take up the space. Algal cover increased 20% in that time period. The transition from coral dominance to algae dominance within a reef community decreases the biological and physical complexity of coral habitat. This is vital for ecosystem services.
What are the prospects for coral reefs in the future?
It is not the end of the story that coral reefs have been losing their live hard coral coverage over the last 40 years. Coral reefs are highly vulnerable to further declines due to future ocean warming projections and increased coral bleaching. Most coral reefs will experience coral bleaching by 2030s. This could happen at least twice per decade and perhaps every year until 2040s. This would stop coral recovery between episodes. Coral reefs could be extinct by 2100 if there isn’t a drastic change.
Although this might seem grim, there are some signs of hope. Improved management and understanding of reefs can improve resilience and prevent worst-case scenarios.
Among other studies, the GCRMN report shows that coral reefs can recover in certain conditions. Coral reefs that have a high coral diversity and coral cover may be more resistant to rising ocean temperatures than others. It is important to reduce local and global pressures on corals reefs in order to recover and sustain their resilience. This includes managing dredging, minimizing pollution, sedimentation, and preventing reef damage.
Networks Scientists, coastal managers, and conservation professionals are all working together to understand what factors contribute to coral survival and recovery. There are many approaches being tried, including:
- An amplifying of warnings about impending high sea surface temperatures. These alerts indicate when corals will be experiencing stress. This helps coastal managers reduce local threats.
- Strategic development of marine protected zones (MPAs). Protected areas allow reefs to survive and reproduce. Coral larvae from protected areas can then drift into the reefs and help them repopulate.
- This can disperse heat-tolerant alga to bleached coral reefs.
Coral reefs are becoming more protected by being included in expanded and new MPAs. Additionally, more coral reefs are located in ” fully protected and highly protected areas”, which often include areas where fishing is prohibited. Good management practices, such as the establishment of “no-take” zones that restrict the use of resources (living or dead), as well as practices to reduce pollution and disturbance within these areas, can help reduce local threats and increase coral resilience. Global actions to control global warming and reduce greenhouse gas emissions will also be beneficial to the reefs.
Reef protection requires tools that increase knowledge about coral reefs and address global and local threats. This knowledge and increased understanding of coral reefs and the threats they face, as well as their immense value, is especially important for reef protection.
Stakeholders on the ground will benefit from tools that give insight into regional interactions. The Coral Reef Regional Dashboards contains the most sought-after data for supporting decision-making related to coral reefs. These dashboards give an overview of coral reefs’ value for tourism, fisheries and shoreline protection. They also provide information about the reef dependent population and the social and economic vulnerability of those living in the area to coral decay. The dashboards also include information about the extent of coral reef habitat and mangrove habitat as well as details on how many are in MPAs or fully protected areas. The dashboards also include indicators and mapping of future and current threats locally and globally. They summarize current knowledge regarding changes in the area’s live coral cover and algal coverage.
What can be done to ensure the coral reefs’ future?
There is no single solution to save coral reefs. Many coordinated actions must be taken in order for corals to survive.
Locally, coral reef threats can be addressed by managing fisheries sustainably and eliminating all forms of fishing. Management and financial support for MPAs, and other area-based conservation measures, must be more efficient and connected. Different departments should recognize potential areas for coordination.
To reduce the likelihood of coral bleaching or acidification, global efforts must be made to limit warming to 1.5 degrees Celsius. Although international climate conferences like the United Nations Framework Convention on Climate Change are bringing more attention to the ocean, there is still little progress. It is important that ocean environments such as coral reefs are given more attention in climate mitigation strategies.
Tools that assist global leaders and regional policy makers can provide new hope for coral reef protection. Although these changes won’t be easy to make, they are necessary in order to save coral reefs.