{"id":63916,"date":"2020-10-16T08:57:22","date_gmt":"2020-10-16T06:57:22","guid":{"rendered":"https:\/\/www.sonnenseite.com\/?p=63916"},"modified":"2020-10-16T08:57:22","modified_gmt":"2020-10-16T06:57:22","slug":"the-great-barrier-reef-has-lost-half-its-corals","status":"publish","type":"post","link":"https:\/\/www.sonnenseite.com\/en\/science\/the-great-barrier-reef-has-lost-half-its-corals\/","title":{"rendered":"The Great Barrier Reef has lost half its corals"},"content":{"rendered":"\n

A new study<\/a> of the Great Barrier Reef shows populations of its small, medium and large corals have all declined in the past three decades.<\/p>\n\n\n\n

Lead author Dr Andy Dietzel, from the ARC Centre of Excellence for Coral Reef Studies (CoralCoE), says while there are numerous studies over centuries on the changes in the structure of populations of humans\u2014or, in the natural world, trees\u2014there still isn\u2019t the equivalent information on the changes in coral populations.<\/p>\n\n\n\n

\u201cWe measured changes in colony sizes because population studies are important for understanding demography and the corals\u2019 capacity to breed,\u201d Dr Dietzel said.<\/p>\n\n\n\n

He and his co-authors assessed coral communities and their colony size along the length of the Great Barrier Reef between 1995 and 2017. Their results show a depletion of coral populations.<\/p>\n\n\n\n

\u201cWe found the number of small, medium and large corals on the Great Barrier Reef has declined by more than 50 percent since the 1990s,\u201d said co-author Professor Terry Hughes, also from CoralCoE.<\/p>\n\n\n\n

\u201cThe decline occurred in both shallow and deeper water, and across virtually all species\u2014but especially in branching and table-shaped corals. These were the worst affected by record-breaking temperatures that triggered mass bleaching in 2016 and 2017,\u201d Prof Hughes said.<\/p>\n\n\n\n

The branching and table-shaped corals provide the structures important for reef inhabitants such as fish. The loss of these corals means a loss of habitat, which in turn diminishes fish abundance and the productivity of coral reef fisheries.<\/p>\n\n\n\n

Dr Dietzel says one of the major implications of coral size is its effect on survival and breeding.<\/p>\n\n\n\n

\u201cA vibrant coral population has millions of small, baby corals, as well as many large ones\u2014 the big mamas who produce most of the larvae,\u201d he said.<\/p>\n\n\n\n

\u201cOur results show the ability of the Great Barrier Reef to recover\u2014its resilience\u2014is compromised compared to the past, because there are fewer babies, and fewer large breeding adults.\u201d<\/p>\n\n\n\n

The authors of the study say better data on the demographic trends of corals is urgently needed.<\/p>\n\n\n\n

\u201cIf we want to understand how coral populations are changing and whether or not they can recover between disturbances, we need more detailed demographic data: on recruitment, on reproduction and on colony size structure,\u201d Dr Dietzel said.<\/p>\n\n\n\n

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\u00a9 ARC Centre of Excellence for Coral Reef Studies \/ Andreas Dietzel<\/figcaption><\/figure>\n\n\n\n

\u201cWe used to think the Great Barrier Reef is protected by its sheer size\u2014but our results show that even the world\u2019s largest and relatively well-protected reef system is increasingly compromised and in decline,\u201d Prof Hughes said.<\/p>\n\n\n\n

Climate change is driving an increase in the frequency of reef disturbances such as marine heatwaves. The study records steeper deteriorations of coral colonies in the Northern and Central Great Barrier Reef after the mass coral bleaching events in 2016 and 2017. And the southern part of the reef was also exposed to record-breaking temperatures in early 2020.<\/p>\n\n\n\n

\u201cThere is no time to lose\u2014we must sharply decrease greenhouse gas emissions ASAP,\u201d the authors conclude.<\/p>\n\n\n\n