29 July 2010

Marine biodiversity and sea surface temperature

A study looked, for the first time, at global marine biodiversity patterns for over 11,000 marine species. Among coastal creatures, including corals and mangroves, the greatest area of diversity, or hotspots of diversity, for most species groups was around the tropics of Southeast Asia.
Biodiversity map of coastal and oceanic marine creatures, red boxes mark hotspots of biodiversity/ Tittensor.

Much research has been conducted on diversity patterns on land, but knowledge of the distribution of marine life has been more limited. This has changed through the decade-long efforts of the Census of Marine Life, upon which the current paper builds.

The study included major species groups such as corals, fishes, whales, seals, sharks, mangroves, seagrasses, and zooplankton. In the process, the global diversity of all coastal fish species has been mapped for the first time.

"We wanted to find out which species were where, and why some places were greater hotspots of diversity than others," said lead researcher Derek Tittensor. "We were also interested in how these newly mapped hot spots related to human impacts on the oceans."

What the study found worrying was that these same hot spots of marine life overlapped areas with the largest human footprints, which raises the threat of severe species losses from pollution and other human action. Meanwhile, the combined effects of pollution, exploitation and habitat destruction put at risk the benefits humans gain from diverse ecosystems, such as water filtration and fish protein.

Of all the factors the study looked at to explain why some regions had more or fewer types of creatures, the only factor that consistently explained the patterns for the 13 groups of marine life they studied was temperature.

“It was surprising that we found such a strong correlation to marine biodiversity and temperature,” said Tittensor. “You might expect a different response to temperature from cold and warm-blooded animals, for example.”

Since sea-surface temperature stood out as the only factor that consistently influenced all species groups, it suggests that climate change could rearrange the distribution of oceanic life. Warmer parts of the ocean, for example, tended to sustain greater species diversity. But at the extremes of the temperature scale, Tittensor said, biodiversity may no longer be increasing. Instead it may be reaching a plateau or declining.

Derek P. Tittensor, Camilo Mora, Walter Jetz, Heike K. Lotze, Daniel Ricard, Edward Vanden Berghe & Boris Worm. Global patterns and predictors of marine biodiversity across taxa. Nature, July 28, 2010 DOI: 10.1038/nature09329

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