Newswise — New research suggests that as global temperatures rise, the lethal coral disease is spreading and is expected to establish itself universally on reefs within the coming century.
The recently published study in Ecology Letters demonstrates the severe impact of climate change on coral well-being, posing a significant threat to the survival of entire reef ecosystems and causing devastating consequences for coastal communities.
To conduct the meta-analysis, experts from UNSW Sydney examined 108 studies that focused on coral health, surveying coral reefs for signs of disease. By correlating the findings of these disease surveys with oceanic sea surface temperature data, the researchers gained insights into the impact of climate change, particularly ocean warming, on the global prevalence of coral diseases. Additionally, they employed modeling techniques to project the potential spread of diseases under different scenarios of future warming.
The study revealed a significant correlation between rising ocean temperatures and the escalation of coral diseases over the years. The prevalence of coral disease has tripled globally over the past 25 years, reaching 9.92 percent. Furthermore, the researchers' modeling indicates a potential surge in disease prevalence to 76.8 percent by the year 2100 if temperatures continue to follow the current trajectory—an alarming projection based on the most conservative worst-case scenario.
Samantha Burke, the study's lead author and a PhD candidate at the School of Biological, Earth & Environmental Sciences, emphasizes that the results underscore the catastrophic consequences of increasing temperatures on coral reefs. She emphasizes the urgent necessity for immediate measures to address and alleviate climate change in order to protect these delicate ecosystems.
Ms. Burke asserts that coral disease poses a significant threat to the survival of corals worldwide and contributes to the decline of reef ecosystems. She highlights the modeling results, which indicate that the situation is projected to deteriorate further, even under conservative estimates of ocean temperature changes. This statement underscores the urgency of addressing the issue of coral disease and implementing effective measures to safeguard coral reefs.
The study also suggests coral disease is likely to worsen more in the Pacific Ocean than in the Atlantic Ocean or Indian Ocean based on current data.
According to Ms. Burke, specific oceans face higher susceptibility to coral disease, but it is challenging to determine whether this vulnerability is solely due to rising ocean temperatures or a combination of various other stressors that corals encounter. However, the indisputable fact is that the prevalence of coral disease is increasing worldwide. Without immediate action to address the issue of rising temperatures, the number of diseased corals will continue to rise. This highlights the critical need for urgent measures to combat climate change and protect coral ecosystems.
An ecosystem on the brink
Coral reefs serve as crucial components of the marine ecosystem, providing vital support for approximately a quarter of the world's fish species. They hold immense significance for coastal communities, acting as essential resources for fisheries and tourism. Moreover, these reefs offer valuable protection against storms and coastal erosion, safeguarding coastal regions and their inhabitants. Recognizing the multifaceted benefits of coral reefs highlights the importance of preserving and protecting them for both ecological and socioeconomic reasons.
“They are the habitat builders. Without coral, there is no reef environment and no coastal industry,” Ms Burke says.
Coral disease occurs when the immune system of coral becomes weakened, often due to infection by pathogens such as bacteria or fungi that induce illness in the animal. This condition is distinct from coral bleaching, which transpires when corals undergo stress and expel the symbiotic zooxanthellae algae residing within their tissues. The expulsion of these algae is responsible for the loss of coloration and the corals turning white during bleaching events. While both coral disease and bleaching are detrimental to coral health, they are separate phenomena with distinct underlying causes.
According to Ms. Burke, certain coral diseases exhibit a rapid progression, leading to the eventual death of affected corals. The detrimental impact of these diseases is significant because the establishment of coral reefs is a lengthy process. Consequently, coral populations may not have sufficient time to recover from the disease, resulting in the loss of entire sections of the reef. This highlights the vulnerability of coral ecosystems and the critical importance of addressing coral diseases to prevent the irreversible loss of these vital marine habitats.
Corals are highly sensitive organisms that rely on specific environmental conditions to thrive, including factors like water temperature, salinity, and overall water quality. When these conditions deviate from the optimal range, corals become stressed, leading to various negative consequences. Stressed corals experience reduced growth rates, diminished reproductive capabilities, and ultimately face a heightened risk of mortality. Their sensitivity to environmental changes underscores the importance of maintaining the delicate balance of conditions necessary for their survival and the overall health of coral reef ecosystems.
While coral disease is primarily caused by infectious pathogens such as bacteria and fungi, it is important to note that stressed corals are particularly susceptible to these infections. Environmental stressors, including rising water temperatures, can weaken coral immune systems, making them more vulnerable to disease-causing organisms. Moreover, higher water temperatures can also contribute to the increased virulence or accelerated growth rate of these pathogens. Thus, the combination of stress and elevated temperatures poses a significant risk to the health and survival of coral reefs.
Ms. Burke explains, "As ocean temperatures rise, coral stress intensifies, leading to a diminished immune response." She further highlights that elevated temperatures can create an environment that is more conducive to the growth and activity of disease-causing pathogens.
Several coral diseases are identified based on their visible characteristics, such as black band disease or yellow band disease. However, a significant number of disease-causing pathogens remain unidentified by scientists. Despite recognizing the visible symptoms, the specific pathogens responsible for these diseases have not yet been fully characterized or identified. This knowledge gap underscores the need for further research and investigation to better understand the underlying causes of coral diseases and develop effective mitigation strategies.
Ms. Burke points out that there is still limited understanding regarding whether the microbes found in diseased corals are the primary cause of the disease or if they are merely a consequence of the coral's sickness and dying tissue. While it is evident that the coral is unwell and experiencing tissue deterioration, the exact role of the fungi or bacteria present in either causing the disease or feeding on the decaying tissue remains unclear. Further in-depth studies are required to shed light on this matter and provide researchers with a deeper understanding of coral diseases and their microbial associations.
Ms. Burke emphasizes the importance of conducting additional research on coral disease, highlighting its significance in developing effective interventions to combat these diseases. Furthermore, she underscores that further study will shed light on the intricate nature of the threats currently confronting coral reef ecosystems. Recognizing the complexity of these threats is crucial for implementing comprehensive strategies to protect and preserve coral reefs in the face of increasing challenges.
Ms. Burke asserts that addressing coral disease requires a multifaceted approach that encompasses actions at both large and small scales. She highlights that relying solely on a universal antibiotic or a single solution would not be a viable strategy. Instead, she emphasizes the need for proactive and concerted efforts involving various interventions to combat coral disease effectively. This underscores the importance of adopting a comprehensive approach that considers factors such as reducing stressors, improving water quality, implementing conservation measures, and promoting sustainable practices to safeguard coral reef ecosystems.
Considering the high stakes involved, it is imperative to take significant strides towards the development of effective mitigation strategies for coral disease. Ms. Burke emphasizes that a crucial starting point would be to address the escalating temperatures. Recognizing the pivotal role of temperature in exacerbating coral stress and disease, implementing measures to mitigate and reduce rising temperatures becomes paramount. Taking proactive steps to address this fundamental issue can contribute to the overall preservation and protection of coral reef ecosystems.
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