Tropical Coral Reefs Face Dire Consequences Due to Climate Change
Tropical coral reefs are on the verge of becoming one of the earliest casualties of climate change. The rich marine diversity hotspots are deteriorating rapidly due to various factors associated with global warming. These include ocean acidification, degradation of water quality, diseases affecting reef-building organisms, and their inability to keep up with the projected rise in sea levels.
A team of interdisciplinary scientists from renowned institutions such as Goethe University Frankfurt’s Institute of Geosciences, ReefTech Inc., GEOMAR Helmholtz Center of Ocean Research, University of Ottawa’s Department of Earth and Environmental Sciences, and GSI Helmholtz Center of Heavy Ion Research have recently published their findings in Scientific Reports. The researchers analyzed 22 drill cores obtained from the Belize barrier reef and atolls, the largest reef system in the Atlantic Ocean. By examining the coral growth and accretion rates over the past 9,000 years, they aimed to determine whether the current decline in coral reefs is unprecedented.
Professor Eberhard Gischler, head of the biosedimentology working group at Goethe University Frankfurt’s Institute of Geosciences, and his team reanalyzed the specimens collected by Gischler and Dr. J. Harold Hudson between 1995 and 2002. The drill cores, totaling 215 meters in length, allowed the scientists to reconstruct environmental conditions during the Holocene period, comparing them to previous ecological and environmental conditions. To date the corals, the team employed radioisotope dating, which helped determine the age of each specimen by analyzing the decay rates of radioactive isotopes present within them.
Based on their findings, the researchers discovered that coral accretion rates had decreased over time in Belize. While the average accretion rates of reef margins matched those of other regions in the western Atlantic (3.36 millimeters per year), they were slightly lower than those in the Indo-Pacific. This is significant for tropical island nations, many of which rely on or are protected by coral reef structures. Additionally, these growth rates align with the lower end of the United Nations’ Intergovernmental Panel on Climate Change’s predictions for future sea-level rise by 2100.
The study’s findings further solidify the alarming decline of live coral in the Caribbean. Many reefs are no longer dominated by corals, but rather invasive fleshy algae and weedy, generalistic species. When observing the evolution of the reefs over time, the researchers found that stress-tolerant, reef-building corals thrived in older sections. However, as the reef pedestal became fully submerged and environmental conditions improved, the abundance of these corals decreased.
Furthermore, the team discovered three significant gaps in the fossil record of the fast-growing elkhorn coral Acropora palmata in Belize. These gaps occurred approximately 2,000, 4,000, and 5,500-6,000 years ago. The first and last gaps corresponded with similar Acropora gaps in the Virgin Islands and the wider Caribbean, indicating potentially higher temperatures, increased storm activity, and lower nutrient supply as contributing factors. The 4,000-year gap aligns with a potential mass mortality event of grazing echinoids in the region, which may have led to an increase in fleshy algae. The study’s authors also suggested that this mortality event could be linked to the 4.2-kiloyear event, which caused mid-latitude droughts in North America and elevated sea surface temperatures in tropical oceans.
In conclusion, tropical coral reefs are under severe threat due to climate change. The scientific evidence presented by the international research team highlights the decline of coral reefs in Belize and the Caribbean. The study underscores the urgent need for global action to combat climate change and protect these invaluable ecosystems, which provide habitat for countless marine species and play a vital role in the wellbeing of coastal communities worldwide.
