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roundtable:a modern mass extinction Watch Show 3:
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Of all species that have existed on Earth, 99.9 percent are now extinct. Many of them perished in five cataclysmic events.

According to a recent poll, seven out of ten biologists think we are currently in the throes of a sixth mass extinction. Some say it could wipe out as many as 90 percent of all species living today. Yet other scientists dispute such dire projections.

As our panelists debate the issue, they also consider how one species -- Homo sapiens -- may be triggering a modern mass extinction.

are we in the midst of a mass extinction
  Question submittal is now closed. Please go to the forums to read our panelists' answers to the user questions.
Tundi Agardy (a woman)Tundi Agardy is an internationally renowned expert on marine conservation, specializing in marine protected areas and coastal planning. From 1997 to early 2001, she was senior director for the Global Marine Program at Conservation International, a global environmental organization.

Many marine ecologists would agree we are indeed facing an extinction crisis. This may surprise those who view the seas as vast and immutable -- the one great constant in an ever-changing world. But while there are remote ocean areas that remain relatively pristine, most coastal areas have undergone a radical human-induced transformation in the last 100 years.

The marine extinction crisis is not as widely grasped as the crises in tropical forests and other terrestrial biomes. Though the number of marine extinctions is small, this is due to our state of knowledge. First, the bulk of marine species are undiscovered -- we are losing species before we even know of them. Second, the species label itself does not work well for marine organisms -- here unique populations are at risk, not entire species (the U.S. placing certain runs of salmon on the endangered species list exemplifies this). As with species extinction, the devastation of genetically unique populations is an irreversible biodiversity loss.
Marine biodiversity is reduced by both over-exploitation of living resources and the much more insidious and dangerous loss of habitat. Nearly three-quarters of the world's commercially fished stocks are overharvested and at risk. At the same time, habitat loss is a chronic and much more acute problem, with grave consequences for marine life and the entire biosphere. The most ecologically essential habitats -- estuaries, wetlands, shallow water seagrasses, and coral reefs -- are most threatened. Thirty percent of the world's mangrove forests and nearly half the world's coral reefs have been lost due to direct habitat destruction. Many of the remaining critical marine habitats are indirectly degraded by pollution, freshwater diversion, and climate change. As human population pressures grow, essential ecological services and species are affected, leading to conditions in which the planet's vital organs can serve neither nature nor us.
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