Coral reefs have generated more new kinds of animal than all other marine habitats put together. So concludes an analysis of the earliest fossils of more than 6000 sea-floor invertebrates, which found that reefs 鈥済ave birth鈥� to close to 6 in 10 of the groups studied.
Coral reefs house a striking number and variety of organisms. Debate has raged over whether they provide the ideal conditions for new species to emerge or simply attract them from other habitats. Until now, the latter argument has tended to prevail.
鈥淥ur new finding suggests that the opposite is true,鈥� says of the Leibniz Institute for Research on Evolution and Biodiversity at the Humboldt University in Berlin, Germany.
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鈥淲hen we lose our coral reefs, we lose not just the ocean鈥檚 most beautiful harbours of life but also any chance we have of recovering the species the world is predicted to lose in the coming biodiversity crisis.鈥�
Studies have shown that humans have already destroyed most of the world鈥檚 reefs through activities such as dynamite fishing, pollution and unsustainable tourism.
Spineless study
Kiessling鈥檚 team looked for the earliest fossil evidence of 6615 genera of sea-floor invertebrates such as clams, sea snails, trilobites, crabs and corals to see where the animals had first emerged. The fossils studied dated all the way back to the Cambrian explosion of evolutionary diversity some 540聽million years ago. Fish and squid were excluded because ocean currents can carry their bodies far from where they died before they fossilise.
Of the genera analysed, 22聽per cent originated in or around reefs. After correcting for the rarity of reefs compared with other marine environments, Kiessling concluded the true proportion to be close to 60聽per cent. Of those that evolved on reefs, over 65 per cent of such genera were then 鈥渆xported鈥� to other marine habitats.
It is not clear is why coral reefs are such prolific generators of biodiversity. 鈥淩eefs provide complex, three-dimensional habitats that are rich in niches and can support lots of different species,鈥� suggests Kiessling.
Coral reef ecosystems are particularly vulnerable to environmental change and so suffer more extinctions than other environments 鈥� which, paradoxically, may further increase their fecundity. 鈥淗igh extinction rates of reefs offer additional opportunities for new species to originate,鈥� says Kiessling.
What鈥檚 more, the nutrient-poor water common around coral reefs keeps populations small 鈥� and small populations, isolated by a barrier such as a reef or a sandy bottom, are more likely to diverge into new species.
Life motor
鈥淭his study raises the possibility that it鈥檚 not just the tropics but tropical coral reefs in particular that are the evolutionary motors of marine diversity,鈥� says , who researches the evolution of marine diversity at the University of Chicago.
, who runs the Paleobiology Database at the National Center for Ecological Analysis and Synthesis in Santa Barbara, California, says, 鈥淲e all know that the fossil record is incomplete, and it鈥檚 hard to do an analysis like this one without addressing that problem. But I think they did address those concerns fully, so the patterns are likely to be real.鈥�
The records were mined from the , a vast archive of over 1聽million fossil finds. As well as reefs, they looked at calcium carbonate sediment, siliciclastic sediment such as shale, clay or sandstone, and in waters both tropical and non-tropical, shallow and deep.
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