From The Economist - May 11th - 2019

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Extinction



Dead end



A new report confirms that life on Earth is in trouble


A million species of animals and plants are threatened with extinction. Three-quarters of the world's land and two-thirds of its marine environments have been "significantly altered" by human action. Urban areas have doubled in size in just the past 30 years. More than 85% of wetlands have been lost. More than 90% of ocean fish stocks are being harvested at or above sustainable levels. These are among claims made in a report published on May 6th by the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services, a big international quango.


The report, based 15.000 research papers, makes grim reading. More than 40% of amphibians are threatened with extinction, as are a third of marine mammals, a third of sharks and a third of corals (a novel idea for the protection of which is described in the next story). Even 10% of the world's insects are on the brink.


A cynic might suggest that 1m is a suspiciously headline-grabbing figure. It is, indeed, only a little short of the number of animal and plant species (around 950,000 and 200,000 respectively) currently recognised and described by science. And its accuracy depends on many assumptions. But it is probably not a bad guess.


A consensus is emerging of there being some 8m species of animals and plants (the report ignores bacteria, fungi and unicellular creatures like Amoeba). Using figures from the International Union for Conservation of Nature (IUCN), which publishes an annual Red List of Threatened Species, the report's authors looked at the proportion of threatened species in well-studied groups of organisms and extrapolated.


In those groups, the IUCN reckons around a quarter of species are at risk of extinction. Many of the best-studied groups, however, are vertebrate animals, while most animals are invertebrates. Extrapolating from vertebrates to invertebrates is risky. The authors therefore made an exception for insects, the most speciose group (5.5m of the 8m purported species). For these they suggest 10% might be threatened with extinction—a figure in line with one derived by combining data on habitat degradation with the known relationship between habitat area and species numbers. This suggests 9% of terrestrial animals (most of which are insects) are threatened with extinction. Add the figures up and a bit over 1m is what you get. Depressing. ■




Please do not bleach

An idea to save coral reefs from from climate change takes a step forward




Bleaching is bad for coral. It happens when heat-stressed polyps, the sessile animals that construct coral reefs, eject the photosynthetic algae which usually reside within them. These algae are symbionts, providing nutrients to their hosts in return for shelter, so losing them is harmful to polyps and often results in their death. The higher temperatures brought about by global warming have therefore led to worries that more frequent episodes of bleaching might result in the loss of entire reefs.


Some of these symbiotic arrangements between alga and animal are, however, more heat-sensitive than others. It might therefore be possible to save reefs by seeding them with heat-resistant symbioses. As temperatures rose, these biological partnerships would spread and the reef they had been transplanted to would survive. Two researchers studying this idea are Megan Morikawa and Stephen Palumbi of Stanford University, in California. And they have just published a paper in the Proceedings of the National Academy of Sciences which suggests that it might work.


Dr Morikawa and Dr Palumbi started by collecting 20 representatives of each of four types of coral from a lagoon off the coast of American Samoa. They picked the lagoon in question because it was small and shallow, and thus had limited water circulation. This meant it often experienced temperature spikes, so any corals living within it would be expected to be adapted to endure such spikes. Laboratory tests proved those expectations correct.


The researchers then picked a second reef, 3km from the original lagoon, which had similar mean temperatures over the year but experienced lower daily temperature fluctuations. They seeded this with 400 fragments derived from their collected samples and a further 400 that were not heat-resistant, to act as controls. The original plan had been to let these transplanted corals grow for a while in their new environment and then bring them back to base for testing. Nature, however, intervened. Eight months after the seeding, soaring temperatures caused extensive bleaching on the reef.


Their hands thus forced, Dr Morikawa and Dr Palumbi put on their scuba gear and went diving to see how their transplants had fared. They found that those from resistant colonies were between a half and a third as likely to have become bleached as were the controls. Moreover, when they returned to the parent corals in the shallow lagoon and looked at the health of these after the bleaching event, they found that the experience of the parents tended to match that of their offspring. The eight months of acclimatization and growth the transplants had undergone had not, in other words, eliminated the heat tolerance they inherited from their parent colonies.


Though eight months is not that long, this result is encouraging. Dr Morikawa and Dr Palumbi now plan an extended study in Palau. If that proves successful, then the idea of saving reefs by seeding them with heat-resistant strains will have received a significant boost.

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