Coral reef growth cannot keep pace with sea level rise – Eurasia Review

Tropical coral reefs could end up being among the first victims of climate change. Marine biodiversity hotspots are threatened and declining as a result of global warming, ocean acidification, water quality degradation and diseases of reef-building organisms.

These are some of the conclusions drawn by an interdisciplinary team of scientists from 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 HelmholtzSI Helm. Center for Heavy Ion Research. Their findings are based on a study of 22 drill cores collected from the Belize Barrier Reef and coral reefs, the largest reef system in the Atlantic Ocean, focused on identifying and dating coral growth and growth rates over the past 9,000 years.

Professor Eberhard Gischler, head of the Biophotographic Working Group at Goethe University Frankfurt’s Institute of Geosciences, and other scientists joined Gischler and Dr. J. Harold Hudson, Miami, USA, reexamined specimens collected between 1995 and 2002. Studying the drill cores — a total of 215 meters — „allows us to create detailed and systematic reconstructions of the environmental conditions that prevailed during the Holocene, based on which we can reconstruct past environmental and ecological conditions. Determine whether the current coral and coral reef collapse is truly unprecedented,” Kishler says. Pooling their expertise, they identified and dated 127 coral fragments using radioisotope methods, and statistically analyzed changes in coral community structure over time based on more than 1,100 fossil corals. Radioisotope dating allows scientists to determine the age of an object by noting the decay rates of radioactive patterns present in the sample.

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After dating the corals, the team identified the distances between them in drill cores to estimate their growth rates. „Our data show that coral accretion rates have decreased in Belize during the Holocene. Although at 3.36 millimeters per year, average accretion rates of reef margins are in the same range as elsewhere in the western Atlantic, and slightly lower than in the Indo-Pacific. This is a potential future threat to tropical island-states. has an important impact, especially where they are based on or protected by coral reef structures, and is also interesting in the context of climate change, Kishler explains.

Research confirms the severe decline of live coral reefs in the Caribbean, where many reefs are not dominated by corals, but by succulent algae and weeds, common taxa. Looking at evolution over time, Kishler and his colleagues found that stress-resistant, reef-forming corals dominated the older sections. „At the base of our cores, directly above the Pleistocene reef limestone, Pseudodiploria Brain corals And Arbicella Star corals are more common, illustrating that members of stress-tolerant taxa are clearly dominant,” explains Kishler. Once the reef bed is completely submerged and environmental conditions improve, the number of these types of corals declines.

The shift from stony corals to succulent algae and from common reef builders to weedy taxa underscores the importance of fecundity for the coral community to cope with increasing environmental stress.

Pre-human intervals in development

Another interesting detail discovered in the drill cores is that there are three century-sized gaps in the fossil record of the fast-growing, competitive „Elkhorn Reef.„Acropora palmata.” In Belize – about 2,000, 4,000, as well as today 5,500-6,000 years ago. Both the first and last of the intervals are congruent Acropora Gaps in the Virgin Islands and the wider Caribbean may point to periods of higher temperatures and increased storm activity and lower nutrient supply, the researchers say.

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In contrast, an interval of about 4,000 years before present coincides with a mass die-off of grazing echinoids in the region, which may have led to an increase in the abundance of succulent algae during this time window. Another possible reason put forward by the study’s authors is that the deaths are linked to the so-called 4.2K-event, which is thought to have caused mid-latitude droughts in North America and raised sea surface temperatures in the tropical oceans.

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