This course surveys the diversity, structure and functioning of California’s ecosystems through time and the ways they have influenced and responded to human activities and stewardship. Topics include ecosystem drivers such as climate, soils, and land use history; human and ecological prehistory of the state; comparative marine, freshwater, and terrestrial ecosystem dynamics; and managed ecosystems such as range, fisheries and agriculture in California. The course also emphasizes important skills to understand as a scientist or consumer of scientific information, including data collection, natural history, and writing.
Kelp Forests
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From the course by University of California, Santa Cruz
Ecosystems of California
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From the lesson
Marine Systems
Meet the Instructors
Erika ZavaletaProfessor
Ecology and Evolutionary Biology
[MUSIC]
I'm Erica Zavaleta and this is Ecosystems of California.
The three-dimensional world of kelp forests
is one that most people only view from the top.
The mirror of terrestrial forests that most people only view from the bottom.
In both cases there's a tremendous amount of vertical structural diversity present.
With canopy, sub-canopy, and understory species.
Epiphytes living at all different levels of that structure.
And consumers specializing in the parts that occur
at different points along that vertical spectrum.
Kelp forests globally are found in areas with relatively cool,
nutrient rich waters, at least part of the time.
And they're especially prevalent in areas with strong upwelling,
like here on the California coast.
They require shallow rocky reefs.
And they can occur anywhere from very shallow waters
all the way down to 40 meters in depth.
There are five canopy forming kelp species in kelp forests in North America.
Four of them occur in California.
This is the giant kelp, bowl kelp, and its southern species
and the feather bowl kelp.
And of those four, two are the main canopy producing species,
In most of California's kelp forests, the bowl kelp and the giant Kelp.
Kelp forests are incredibly productive ecosystems.
And that productivity is fueled by the kelp itself.
So, anchored to the bottom are the benthos by a holdfast.
Kelp are spared from having to invest a lot into structural tissue to support
their height because of the water holding them up.
So, they can instead invest a lot into the growth of their blades,
these large surface area, thin, photosynthesizing surfaces that
are up near the sunlight and produce lots and lots of energy that they can
then translocate to depths where the sunlight may not really reach.
Because they don't have to invest a lot in structural tissues kelp can grow on
the order of a meter per day during the most productive times of year.
So in that way kelp forests subsidize not only a lot of consumers and
productivity within kelp forests themselves, but they also subsidize other
more heterotrophic ecosystems, including beaches like the one that I'm sitting on,
where kelp that washes up on the beach undergirds a community of consumers, and
the subsidization of fishery species that are favored offshore and
that are produced in the kelp forest.
Below the canopy, other species of kelp, like sea palms and laminaria,
form a sub-canopy, anywhere from about one to three meters above the bottom.
And then finally, there are species of prostrate kelp that inhabit the benthos,
the very bottom.
And provide habitat for fish and invertebrates.
Now the phrenology of kelp, the timing of its bio mass and
events over the course of the year is shaped by upwelling, nutrient
availability, wave action, temperature, and daylight among other things.
In California, a typical lifecycle for the kelp forest Is one where adult
kelp individuals are ripped out by winter storms and so its biomass declines.
And then in the summer, as those storms subside, day length is long,
temperatures are warm, a lot of production can occur with maximum biomass and
productivity happening in late summer and early fall.
Kelp forest ecosystems have a pretty interesting food web structure
because they have two bases.
On one hand the upwelling of nutrients and so
on supports a lot of production by the kelp itself.
And so one base of primary production are the kelps, and
they support a variety of consumers including grazers on the kelp.
Detritivores like abalones and certain kinds of sea stars, and
then fishes that are eating those animals.
But there's another entry point for
primary production to the system because the other really important space
inhabiting organisms in kelp forests aren't plants at all.
They're filter feeding invertebrates.
Things like urchins that actually use phytoplankton out of the water column for
their base of primary production.
So phytoplankton support a different pathway of production in the kelp forest
whereby phytoplankton are consumed both by planktivorous fishes, like rock fishes,
and by all of those bottom dwelling, filter feeding invertebrates.
And then those in turn move up the food web into carnivorous, fishes,
and sea stars, and finally apex predators.
Which include things like the sunflower star, see otters, and the Moray eel.
As well as lots of non-resident predators that play a role.
Such as sharks and harvest eels.
Sea otters were hunted nearly to extinction early in California's history.
And their decline heavily affected kelp forest ecosystems.
Sea otters feed heavily on invertebrates like sea urchins
that are grazers on the kelp.
So without the sea otters, those populations of sea urchins and
other invertebrates really exploded.
With so many grazers, the kelp individuals got eaten down or overgrazed.
And what was left in place of the kelp forests were low productivity,
relatively low diversity.
And structurally simple urchin barrens.
And other benthic ecosystems.
So with the recovery of otters in recent decades, kelp forests have come back and
are much more widespread in California than they were
in that period of otter decline.
And all of that demonstrates what an important role the otters play as
a keystone species, a species that impacts its ecosystem dynamics,
really out of proportion to its numbers in biomass.
[MUSIC]
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