[Jane Watson] So when otters eat urchins,
they set about a huge cascade of changes
in near-shore ecosystems, and a lot of those
changes are really dramatic and they're
important changes. So in many cases, I
think they're changes that we've forgotten
about. So sea otters eat urchins. The kelp
grows very, very quickly, and I always tell
people they should appreciate kelp
because it does a lot of amazing things.
Perhaps the most important thing it does is
it increases the productivity of near-shore
ecosystems. It's essentially dumping carbon
into that system. And it's doing that by
leaking into the water and it's also
breaking up into tiny little fragments,
which in turn feed entire food webs that
really are absent in systems without otters.
And these are detritus-based food webs. So
this is when we get little animals, we call
them detritivores, because they're eating
kelp that are now feeding on that detritus.
Those little tiny animals in turn go on to
feed bigger animals.
So that's the first thing kelp does, is
increase productivity.
The second thing kelp does it's like any
terrestrial forest. As that kelp grows
towards the surface of the water, it
provides habitat for all sorts of fish, for
other animals, for things that live on the
surface of kelp, for herring to spawn on.
And there's been a lot of studies for 
example done showing that there are far more
fish in kelp forests than in areas that are
dominated by urchins. So number two thing,
otters make kelp, kelp increases habitat.
The third thing that kelp does that's a
really interesting thing that we never think
about is it slows down the movement of
water. So as water comes through a kelp
bed, it's slowed down. And that means that
organisms that are living in that forest—
say they're spawning and releasing their
larvae—those larvae are now going to be
entrained and retained in that kelp forest.
Because the water movement has been slowed
down. Instead of being scattered off to
inappropriate habitat, they're now caught
in that kelp forest.
The fourth thing kelp forests do is they're
natural breakwaters. They stop coastal
erosion. You've probably heard about the
kelp highway, this idea that people may
have come into North America along the
fringe of coastal British Columbia, traveling
along kelp. It would have been a beautiful
still ocean inside that kelp fringe.
Those are the four really important things
that kelp does, and that kelp is of course
made by sea otters eating urchins.
