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[♪ peaceful chord ♪]
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[whales grunting]
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[whale calls]
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[whales grunting]
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[whale calls]
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-[narrator] One of the most exciting
scientific findings of the past half-century
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has been the discovery
of widespread trophic cascades.
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A trophic cascade is
an ecological process
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which starts at the top
of the food chain
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and tumbles all the way
down to the bottom.
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We all know that whales
eat fish and krill,
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and some people-- certain
politicians in Japan, for instance--
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have argued that killing whales
is good for human beings,
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as it boosts the food
available for us to eat,
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and so you would think.
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But as the great whales declined,
so did the numbers of fish and krill.
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It seems counter-intuitive--
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surely their numbers would rise
as their major predators disappeared.
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But it now turns out that whales
not only eat these animals;
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they also keep them alive.
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In fact, they help to sustain
the entire living system of the ocean.
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Whales feed at depth in waters
that are often pitch dark,
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and then they return to the surface,
to the photic zone,
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where there is enough light
for photosynthesis to happen.
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There they release
what biologists call "fecal plumes,"
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vast outpourings of poo--
poonamis!
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These plumes are rich
in iron and nitrogen,
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nutrients which are often very scarce
in the surface waters,
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and these nutrients
fertilize the plant plankton
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that lives in the only place
where plants can survive:
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the photic zone.
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Fertilizing the surface waters
isn't the only thing the whales do.
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By plunging up and down
through the water column,
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they also keep kicking the plankton
back up into the photic zone,
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giving it more time to reproduce
before it sinks into the abyss.
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Even today, the whale populations
have been greatly reduced,
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the vertical mixing of water
caused by movements of animals
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up and down through
the column of the oceans
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is, astonishingly, roughly the same
as the amount of mixing
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caused by all the world's
wind and waves and tides.
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More plant plankton means
more animal plankton,
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on which the larger creatures
then feed.
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In other words, more whales
means more fish and krill.
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But the story
doesn't end here
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because plant plankton not only
feeds the animals of the sea,
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it also absorbs carbon dioxide
from the atmosphere.
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When eventually it sinks
to the ocean floor,
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it takes this carbon
out of circulation,
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down to a place where it remains
for thousands of years.
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The more whales there are,
the more plankton there is.
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The more plankton there is,
the more carbon is drawn out of the air.
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When whales were at
their historical populations,
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before great numbers
of them were killed,
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it seems that they might
have been responsible
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for removing tens of millions
of tons of carbon
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from the atmosphere
every year.
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Whales change the climate.
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The return of the great whales,
if they're allowed to recover,
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could be seen as a benign form
of geo-engineering.
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It could undo some of
the damage we have done,
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both to the living systems of the sea
and to the atmosphere.
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[♪ peaceful music ♪]
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[whale calls]
