Hello marine biology students.
In this video, we're going to talk about kelp
forests.
[Intro Music]
So we've discussed the soft-bottom intertidal
and seagrass meadows.
Now let’s spend some time talking about
the hard-bottom subtidal and kelp forests.
The hard-bottom subtidal communities are actually
less common than soft-bottom communities,
and they usually develop along submerged rocky
shores.
In contrast to the soft-bottom communities,
the hard-bottom
communities are dominated by epifauna and
seaweeds in shallow water.
Space is highly competed for on a hard, rocky
bottom with community interactions
influencing the distribution of organisms
in addition to larval settling.
Grazers and predators shape community distribution
as well.
Sea urchins are one of the main grazers on
hard, rocky-bottom communities.
There will be a greater amount of seaweed
growing because a presence of hard substrate
and a greater number of herbivores feeding
directly on the seaweeds or on detritus as
well.
Phytoplankton will also be abundant, and the
filter feeders will be able to feed both on
the phytoplankton and on the detritus.
The carnivores in turn feed on these primary
consumers.
We call hard-bottom communities that are dominated
by brown algae, kelp forests.
Kelps come in a variety of shapes and sizes,
but most of them grow to be very large.
They develop only on rocky bottoms in water
as deep as light allows.
They’re fast-growing, some growing as many
as 20 inches a day, and they may also form
a floating canopy.
Kelp forests are sites of high primary production.
In the North Atlantic, the most common species
of kelp are in the genus Laminaria, which
is one of the smaller species of kelp, with
maximum heights of around 3 meters.
On the Pacific coast of North and South America,
the most common kelp is the giant kelp, Macrocystis.
They can form thick, complex forests with
very high species diversity.
Some of these Macrocystis can grow over 30
meters in length.
Kelp requires cold waters, and so we will
find these kelp where there are cold surface
currents in the oceans.
There is high species diversity within the
kelp community, and there is complex zonation,
much as you would see in a terrestrial forest,
with different organisms living on the bottom
or up in the canopy or even on the growing
structures themselves.
In a kelp community, sea urchins are very
important herbivores, and the organisms that
prey on herbivores also play an important
role in balancing the community.
While urchins feed directly on kelp, many
other members of the kelp community feed on
small little pieces of kelp that have broken
off the larger.
This is called drift kelp, and it is an important
source of detritus, which feeds many members
of the community.
We see zonation in kelp forests not only in
distance from shore but also depth in water.
As we saw in seagrass meadows, sea otters
also play a key role being a keystone predator
in these communities.
They're able to keep the urchin numbers down,
resulting in lush kelp density.
However, as the number of sea otters drop
in abundance either from predation of other
predators or because of humans, this results
in an increase in the number of urchins and
therefore a decrease in the robust diversity
of the kelp forest.
So that takes us to the end of our discussion
of kelp forests.
Now before our next video, I would like you
to think: what if the geography around you
was determined by the actions of your ancestors?
Well we'll talk about that as we discuss coral
reefs.
See you in the next video.
