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.
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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.
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.
