![]() Using paleoecological analysis and high-precision uranium-thorium (U-Th) dating, we reveal an extensive loss of branching Acropora corals and changes in coral community structure in the Palm Islands region of the central GBR over the past century. However, little is known about past coral mortality before the advent of long-term monitoring (circa 1980s). Hard coral cover on the Great Barrier Reef (GBR) is on a trajectory of decline. U-Th dating reveals regional-scale decline of branching Acropora corals on the Great Barrier Reef over the past century.Ĭlark, Tara R Roff, George Zhao, Jian-Xin Feng, Yue-Xing Done, Terence J McCook, Laurence J Pandolfi, John M Our study implies that the management of these reefs may be predicated on a shifted baseline. Collectively, our results suggest a loss of resilience of this formerly dominant key framework builder at a regional scale, with recovery severely lagging behind predictions. Surveys conducted in 2014 revealed low Acropora cover (<5%) across all sites, with very little evidence of change for up to 60 y at some sites. The timing of Acropora mortality was found to be occasionally synchronous among reefs and frequently linked to discrete disturbance events, occurring in the 1920s to 1960s and again in the 1980s to 1990s. In 2008, dead coral assemblages were dominated by large, branching Acropora and living coral assemblages by genera typically found in turbid inshore environments. Roff, George Zhao, Jian-xin Feng, Yue-xing Done, Terence J. U-Th dating reveals regional-scale decline of branching Acropora corals on the Great Barrier Reef over the past centuryĬlark, Tara R. The growth and death of tables thus create local disturbances, and the resulting patchwork of recently shaded and unshaded areas may enhance coral diversity in areas of high coral cover.« less However, table Acropora also have high mortality rates, so that there is continuous production of unshaded areas. The fast-growing but fragile table Acropora are abundant in a wide variety of atoll habitats and grow rapidly to form a canopy approx. Light measurements made beneath table Acropora show that illumination and irradiance values fallmore » to levels at which most hermatypic corals do not occur. Results of experiments in which coral fragments were transferred to the shade of table Acropora and to adjacent unshaded areas show that shading slows the growth and leads to higher mortality of branching species, while massive and encrusting species are unaffected. Additionally, the understory community is predominantly composed of massive and encrusting species, while branching Acropora and Pocillopora predominate in unshaded areas. [ Acropora Pocilloporaįield surveys at Enewetak Atoll, Marshall Islands, show that coral density and diversity is much lower beneath Acropora table corals than in adjacent unshaded areas. ![]() Effect of shading by the table coral Acropora Hyacinthus on understory corals. ![]()
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