(peaceful music)
- [Woman] Let's visit an underwater forest
near Monterey, California,
where kelp grows
over 100 feet tall, reaching
towards the sunlight above.
It's fallen blades litter
the sea floor below,
providing nutrients
for a host of creatures
including these spiny purple sea urchins
which move slowly in search of food.
Sea urchins make a tasty
mean for this marine mammal.
Sea otters help keep the sea
urchin population in check.
Too many sea urchins
will devour living kelp,
destroying the forest.
We consider otters a keystone species.
As active predators they protect kelp
from hungry herbivores like sea urchins
and help maintain diversity
and balance and this ecosystem.
But we're seeing just one small
part of an intricate network.
Sunflower stars also prey on sea urchins
and may become dinner
for a hungry sea otter.
But otters prefer abalone and crabs.
From the smallest microbes
to the largest animals
these species take part
in a diverse food web
that links more than a thousand species.
The connections in the web represent
the transfer of energy with every meal.
At the California Academy of Sciences,
paleontologist Peter
Rutenrein studies both
modern day food webs, like this one,
and those from the past.
- [Peter] Basically a food web is a map
of all of the interactions,
what we call the trophic
interactions, in an
ecosystem or community.
And those are predator prey interactions.
Who eats whom, who eats you,
what do you eat, and so on.
The food web is one of,
if not the most important
representation of interactions
that we have in an ecosystem
because it's a main passage of energy.
Through that system energy
is produced, it's consumed,
and everything else runs on that.
- [Woman] Let's take a closer
look at our marine ecosystem
off the coast of California.
What connections do you
see in this food web?
Can you predict the flow of energy
between otters, urchins, and kelp?
From primary producers to top predators,
this dynamic ecosystem supports
a diverse set of species.
Small changes, however,
can have big impacts
across the entire community.
Imagine you're a citizen
scientist exploring marine
ecosystems on the California coast.
You visit the same kelp forest every year
and observe seat otters, sea
urchins, and kelp populations.
Looking over your field notes
now, what trends do you see?
How are otters, urchins,
and kelp connected?
Take a moment to pause the
video and examine your graph.
Here we see the impact sea otters
have as a keystone species.
When otters are present,
urchin and kelp populations are stable.
When absent though, urchins
boom and kelp beds are reduced.
Let's take another look
at our coastal food web.
Can you predict how a
removal of sea otters
would impact the flow of
energy through the system?
Which species would be
negatively impacted?
Would any be positively impacted?
Pause the video to take a closer look.
Removal of a keystone
species, the sea otter,
has cascading effects,
impacting populations
across multiple trophic levels
and disrupting the flow of
energy through the entire system.
Understanding ecosystems
and the various threads
that connect species together in food webs
can help us better direct
resources for conservation efforts
and, most importantly, come to sustain
these diverse networks of life.
