February 16, 2010

Darwin Days: Biodiversity of the Sea

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While water covers over 70 percent of the earth, land life is 300 times more diverse than sea life. However, the ocean has a wide diversity of species. On Wednesday, in “Evolution and Biodiversity of the Sea,” panelists examined the threat of climate change on the biodiversity of the sea.

Limitations to sea biodiversity include restricted productivity, habitat complexity and weak barriers to dispersal. Still, panelists showcased the evolutionary diversity that lies in coral reef and mollusk phylogenies.

Prof. Catherine Drew Harvell, ecology and evolutionary biology, discussed the effects of pollution level on coral reefs. Reefs include organisms that fascinated Darwin, and he wrote about them extensively.

Coral reefs provide homes to food chains, comprised of diverse “calcifying” organisms, which convert calcium carbonate into shells.

She described how a high concentration of carbon dioxide has lowered water pH, negatively affecting calcifying organisms.

She referenced the Australian reef, where symbiosis between coral and symbiotic algae results in orange and red coral. As carbon dioxide levels rise, pigments turns white. Then, when temperatures drop, coral dies.

“The concentration is higher now than it was 20 million years ago, and it is also higher whenever we see large amounts of extinction,” she said.

She suggested that the question we must ask ourselves. Are we on the edge of mass extinction? She suggested, with a temperature shift of five to six degrees, extiniction is possible.

Prof. Paula Mikkelsen, ecology and evolutionary biology, described the possible threat of mollusk extinction. Since the Cambrian explosion, mollusks have played an important role in the sea’s environment.

With over 120,000 species, and 100, 000 living in the sea, mollusks are the sea’s largest phyla. It includes over 20 times the number of species of mammals. Until recently, scientists have seen no sign of mollusk extinction.

Having survived five major extinctions, mollusks provide an excellent fossil record due to their hard shells. Darwin studied mollusks in the Andes, where he started looking at natural selection.

Prof. James G. Morin, ecology and evolutionary biology, who completes research at Shoals Marine lab, described how many lineages in the ocean world evolved. He discussed how molecular sequences allow for a greater understanding of species, allowing us to distinguish between many similar organisms. While he said the sea may not have as a diverse species population as land, it is very diverse when it comes to phyla.

The panelists showed that variation in the sea is natural but endures a human component. Harvell urged her audience, “We would have to wonder what Darwin would think (about human activity).”

Original Author: Tajwar Mazhar