October 9, 2008
Tectonics Drive Diversity
Tectonic collisions are responsible for the emergence, and decline, of marine biodiversity hotpots, a study has concluded. "By examining fossil and molecular evidence we could clearly see that the global centre of marine megadiversity was over western Europe and Africa in the Eocene, around 50 million years ago," says Prof John Pandolfi of the University of Queensland. "By the start of the Miocene, around 25 million years ago, the hotspot of sea life had moved to the region of the Arabian Peninsula, Pakistan and west India - an area that is still quite rich today."
The global hotspot now stretches from India to Australia. In each case the region was the site of collision between two major tectonic plates. The collisions produced shallow seas filled with bays and islands, creating a network of partially separated ecosystems ideal for species diversity. The hotspot locations and the global climate at the time ensured that all were at temperatures that further encouraged life to flourish.
As the European and African plates came closer, the Mediterranean became constricted and lost the currents that had once promoted species diversification. When Arabia became part of the Asian landmass it eliminated many of the seas in which life had flourished.
"As continents merge tectonically, seas close up, nutrients increase, currents subside and the range of habitats and species also declines," says Dr Willem Renema of the Centre for Excellence for Coral Reef Research. "This period of senescence is of particular interest as it is important to understand whether species richness in a particular area is declining naturally due to tectonic changes or due to man-made changes."
The team measured the rates of appearance of new species of corals, mangroves, shellfish, reef fish and plankton. Contrary to expectations they found that few coral reef species appeared in the last few million years, with most dating to around 20 million years ago.
"Because they occur over such huge time-scales there has been a tendency to discount the role of tectonic changes in the development of life," Pandolfi says, "but we are suggesting here that it is in fact one of the major driving forces".
Marine biodiversity is highest where tectonic plates collide.
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