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.
Estuaries
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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 Erika Zavaleta and this is Ecosystems of California.
Estuaries are the places where rivers meet the sea in an intermingling tidal
system of fresh and salty water.
California has not had many estuaries in it's history because of its steep and
rocky coastline, and it's also lost some of its estuarian systems to
landings change, drainage and diking.
Never the less, California is still home to some spectacular estuary ecosystems.
Some of them are notable for their size.
The San Fransisco Bay Delta Estuary once drained 40% of the state's area,
and itself extended over an area the size of Rhode Island.
Others are notable for the ecosystem services that they provide.
And one example of that is where we're visiting today,
at Elkhorn Slough National Estuarine Research Reserve.
This reserve provides a variety of ecosystem services,
ranging from wildlife habitat for migratory birds, marine mammals, and
rearing sharks and fishes, to services like filtering nitrogen and
phosphorous and other pollutants from agricultural runoff that enters the slough
from the agricultural landscape upstream before it enters the open ocean.
Today we're visiting Elkhorn Slough Reserve, and
we're going to start out with Kerstin Wasson,
who works with the reserve on a variety of restoration and research projects.
>> How our ability to improve global warming has changed.
Estuaries have a variety of habitat types that are almost as different as
grasslands and forests and alpine systems,
they change really dramatically along an elevation of the tides.
So highest step,
we have salt marshes, which are some of the most productive ecosystems on Earth.
Below those are the mud flats, full of worms, and crustaceans, and
small clams that feed migratory shore birds and fish and marine mammals.
And then below that are the channels and creeks,
which remain full of standing water all the time.
Estuaries have been the places that people come to live, because the land is so
productive in the floodplain around rivers where they run into the ocean,
and agriculture is really important in this region.
The lands are very productive.
For instance, farms around the Elkhorn Slough region
supply something like 20% of the strawberries for the whole nation.
But agriculture has had some strong effects on our estuary and ecosystems.
For instance, the Salinas River used to run into the Elkhorn Slough,
providing the estuary fresh water, but
it was diverted to prevent flooding of floodplain fields.
Also, ground water has been used really extensively, and so we don't have these
seeps that give us rushes and sedges on the edges of our salt marshes anymore.
And probably the biggest impact has been through diking and draining,
something like 50% of the estuary area has been diked and
drained, and parts the estuary wetland used directly for agriculture.
A final major impact is from agricultural run off,
pollution from the firm fields enters the system, and
there are pesticides and herbicides, and especially nutrients,
fertilizers that fertilize the estuary, and so, they grow algae, too much of it.
And that's bad for our estuary system, it can decrease the oxygen at night time,
to levels that fish and other animals can't tolerate.
Thousands of visitors come to Elkhorn Slough from all over the world, and
just from the surrounding area, to see the shorebirds up close,
to kayak among sea otters, to experience estuary ecosystems.
And we want to conserve and restore these ecosystems as a legacy for
future generations of visitors.
We're really excited about the Tidal Marsh Restoration Project.
It's the first major marsh restoration project in the estuary,
which has lost something like 50% of its salt marsh over the past 150 years.
So salt marshes occupy a really narrow elevational range in the tidal frame.
If they're too high, they dry out, if they're too low, they drown.
During the history of Elkhorn Slough, when marshes were diked and
drained, and used for cattle grazing, or for farming crops,
the soils in those areas dried out and shrunk, like your kitchen sponge.
And so, later on when nature reserves came in and
returned the title exchange, the salt marsh didn't return.
There were high mudflats and
lagoons in those areas, because the soils were too low.
So what we're going to do is, use beneficial reuse of sediment from
another project that generated sediment and
build the elevation back up to where it needs to be to sustain healthy salt marsh.
And not only that, we're going to go a little bit higher
to make sure the system is resilient in the face of sea level rise.
So hopefully,
a few decades from now, the two sides of this former dyke will look the same.
>> What are some of the ecosystem services that a healthy marsh like this provides?
>> Yeah, there's a whole variety, but as two examples, one is to provide habitat
for wildlife, such as the sea otters that use these creeks for
foraging and haul out on the salt marshes.
At the other end of the spectrum is an ecosystem service that
potentially has global consequences.
It's the blue carbon function of salt marshes.
And that's that salt marshes are able to capture an unusually high amount
of carbon dioxide from the air in their living plant tissues and
then bury it in the sediments of the marsh.
We have some cores that go back to salt marshes from 5,000 years ago.
But for this study we're really focusing on the top layer.
We've been measuring the biomass of the plants per meter squared, and
what's in them on top, so that we can quantify how much
carbon is captured in the plants themselves in the salt marsh.
And then, we've been taking sediment cores, 30 to 50 centimeters
of sediment from the marsh, to measure how much carbon is actually buried.
And the great thing about salt marshes is, that it's buried forever because
as water levels rise each year, the salt marsh grows higher and
new layers of carbon are buried in the salt marsh every year.
>> Thanks so much for showing us around, Kerstin.
>> Yeah, thank you for coming.
We're very hopeful that through conservation, and education, and research,
we can take care of these special estuarine ecosystems.
[SOUND] >> We're
out on the main channel of Elkhorn Slough today with Ron Eby.
Ron is a citizen scientist who's worked at the slough for over a decade now.
Focused on work involving the sea otters who've recolonized the slough in
the last 25 years.
Ron, thanks so much for having us out.
>> I'm glad to have you here.
We're just in the very beginning part of the slough so
we've only gone about a mile and a half so far, but
you can see all the wildlife that we got to see and it's really quite impressive.
I started this by kayaking for
Team Ocean, and one of the things in particular that was different from
the training that I've had was, we were what the otters were doing, and
we show that the otters often are holding out in the beach, mainly at night.
I had a friend, Robert Skulls, and
I decided we start trying to see how much they were foraging there.
At that time we weren't citizen scientists at all,
we were just naturalists observing something.
But what was really fortunate is, we had a scientist take us under her wing and
she told us what we needed to record,
how to record it, how to do it really in a scientific way.
And what we found is, that the otters in the harbor, most of them,
85%, were foraging out in the bay, so
they weren't really coming down to this area, but they were using it as a refuge.
So the colder it got and the more windy it got, the more miserable we were,
the more otters we saw.
We captured 20 otters, put transmitters in them, so we can really determine,
scientifically using the same methods that are done in the ocean,
how much time they spent foraging, how much time they spent resting.
And, because we have those radio signals that we can track them, then we can do
what we call activity budgets, where we follow them for 12 hours a day.
The other thing we do is, foraging budgets, and
that's where we monitor exactly what they're eating.
So we time as soon as they come up with a prey item, how much time
they spend handling it, whether they use a tool to open it, how much time they spend
eating it, how much time on the surface grooming before they dive again, and
then how long it takes them to come up with the next prey item.
And by measuring the prey size, what the prey type is,
we can see what the caloric demands are to do that effort of getting that prey, and
by measuring those animals that we tagged, we know what the caloric gain is.
So we can see how easy it is for them, and we found that.
It's much easier for them to meet their caloric needs here in Elkhorn Slough,
than it is out in the ocean.
You can just imagine, out in the ocean a mother with a pup, she's gotta dive down,
leave the pup on the surface, find the forage, come back up, find her pup,
then eat her prey, in the meantime, she's got all the waves.
But as you can see here, it's just an ideal habitat for the otters.
The really cool thing is, the otters are good for
Elkhorn Slough, they eat the crabs that are in the eel grass,
by getting rid of the crabs the taylor sea hair can survive.
What we have here, is a taylor sea hair, this is a small one,
they can get up to be about the size of my little finger, but
you can see it's been foraging up and down this piece of eelgrass.
They go up and sown the blades of eelgrass and keep eating all the micro algae off.
Then when they get the eelgrass clear like this, then it can photosynthesis.
These plates here, taylor sea hairs have not cleaned them, and
you can see all these micro algae.
We have so much excess nutrients in here that the micro algae just
flourishes like crazy.
The only thing that keeps them in check are these little critters.
Eelgrass is perfect for Elkhorn Slough.
It slows down the currents, which enables more sediment to come out.
Our ebb tides are stronger than our flood tides, so we're losing sediment.
The eelgrass beds help hold that sediment.
And it's an ideal nursery, it's a habitat for all kinds of fish that are out in
the ocean, they grow right here in these eelgrass beds.
Ironically, bringing the top predator back, which is the otter here,
that trophic cascade is back in play.
Otters eat the crabs, slugs survive, eelgrass thrives.
The otter population is stalled, and there's really no where for
them to go right now along the coast.
They only have a two dimensional way to go, and they've only gotten so far and
they're kind of barriers at the end.
But by learning how well they use an estuarine environment, and there are other
estuaries, Morrow Bay up the San Francisco Bay, and where historically there were
more otters just in San Francisco Bay than there are in the whole range now.
So if we learn what we learn here can be applied to other estuaries,
we may find the key to helping the otters break out of a threatened species status.
Otters originally were all up and down the coast, but
what happened is the fur trading began.
The Russians came over and they began killing a lot of them,
selling their furs, the Chinese began doing it, we began doing it.
And with all these different organizations hunting them,
they hunted them almost to extinction.
In fact, it was thought that the southern sea otter,
which is now recognized as a different species, was totally extinct.
Fortunately, there was a small group that lived down off Big Sur and
when they did discover they were there they kept it really quiet.
By then, protections had been created to protect the otters.
So from that small group of 50 to 100 otters, they've been expanding up and
down the coast.
Along the way, at about 1990s, some of them,
they were used to an ocean environment so they weren't used to a place like this,
this was strange, but they began coming here,
first males checking it out, then they left and then the females came in.
Females had their pups here,
females taught their pups how to use an estuarine environment, and
now it's grown to where we have well over 100 otters living right here.
[MUSIC]
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