× close
The top panel shows a coral reef edge in Belize, home to branched Acropora and platy Millepora (Fire) corals, both of which are competitive and fast-growing. The bottom panel shows fertile mound and finger corals overgrown with weeds, and broken branches of dead Acropora coral overgrown with fleshy algae. Credit: E. Gischler
Tropical coral reefs could be the first victims of climate change. Marine diversity hotspots are threatened and in decline as a result of global warming, ocean acidification, water quality degradation and reef-building disease, and their growth is not keeping pace with projected sea level rise.
These are some of the conclusions drawn by an interdisciplinary team of scientists from the Goethe University Frankfurt Institute for Geosciences, Reeftech, GEOMAR Helmholtz Center for Marine Research, the Department of Earth and Environmental Sciences at the University of Ottawa, and the Geographical Institute Helmholtz. Heavy Ion Research Center.
their findingsIt was published in scientific reportis based on examination of 22 drill cores collected from the barrier reef and atoll of Belize, the largest coral reef in the Atlantic Ocean. The study focused on determining and dating coral growth and attachment rates over the past 9,000 years.
Professor Eberhard Gischler, Head of the Biosedimentology Working Group at the Goethe University Frankfurt Institute for Geosciences, and other scientists collected data between 1995 and 2002 by Gischler and Dr. J. Harold Hudson of Miami, USA. The sample was reexamined.
By studying a total of 215 meters of drill core, we have been able to develop a detailed and systematic reconstruction of the Holocene environmental conditions, on the basis of which we can reconstruct earlier ecological and environmental conditions. can. “Determine whether the current coral and reef declines are in fact unprecedented,” Gischler says.
They pooled their expertise and used radioisotope methods to identify and date 127 coral fragments, and based on more than 1,100 fossil corals, they determined changes in coral community structure over time. was statistically analyzed. Radioisotope dating allows scientists to determine the age of material by reference to the decay rate of radioactive samples present in the sample.
After determining the age of the corals, the researchers determined the distances between them in the drill core and estimated their growth rates. “Our data show that coral accretion rates in Belize have decreased during the Holocene. The average accretion rate on reef margins is 3.36 mm per year, which is in the same range as other regions of the western Atlantic; Coral reef accretion rates are slightly lower than in other regions of the Western Atlantic’s Indo-Pacific. ”
This has important implications for the future of tropical island countries, especially those based on or protected by coral reef structures, and is also interesting from a climate change perspective, Gischler explains. “This growth rate is at the lower end of the United Nations’ Intergovernmental Panel on Climate Change (IPCC) predictions for future sea level rise by 2100.”
The study confirms that living corals are in sharp decline in the Caribbean, where many coral reefs are no longer dominated by corals but by fleshy algae and weedy common taxa. . Looking at their evolution over time, Gischler and his colleagues found that stress-resistant reef-building corals predominated in older sections.
“At the base of our core, directly overlying Pleistocene reef limestone, pseudodiplolia brain corals and orbicella star corals were most abundant, indicating a clear predominance of members of stress-tolerant taxa. ,” Gischler explains. However, once the reef pedestal was completely flooded and environmental conditions improved, the abundance of this type of coral decreased.
The authors of this study highlight that the transition from stony corals to fleshy algae, and from common reef-building organisms to weedy taxa, emphasizes the increasing importance of fecundity for coral communities. They point out that this property may help them cope with increasing environmental stress.
Pre-Anthropocene growth gap
Another interesting detail unearthed in the drill core is that the fossil record of Belize’s fast-growing and competitive “elkhorn coral” Acropora has three distinct origins dating back approximately 2,000, 4,000, and even 5,500 to 6,000 years. There is a 100-year gap. Before today.
The first and last gaps coincide with two Acropora gaps in the Virgin Islands and across the Caribbean, researchers said, with possible causes of rising temperatures and increased storm activity, as well as reduced nutrient supplies. It is likely that a decline has been noted.
In contrast, a gap around 4,000 years ago from today coincides with a potential mass mortality of grazing echinoids in this region, which may have caused an increase in succulent algae during this period. . Another possible cause, the authors of this study argue, is that the mortality rate is related to the so-called 4.2k event, which is associated with drought in mid-latitudes of North America and rising sea surface temperatures in tropical oceans. It is believed that this caused the
For more information:
Eberhard Gischler et al. 9000 years of changes in coral community structure and accretion on Belizean coral reefs in the western Atlantic Ocean; scientific report (2023). DOI: 10.1038/s41598-023-38118-5