They are an ancient species of flowering plants
that grow submerged in all of the world’s
oceans from the latitudes of northern Alaska
to the tip of South America.
Seagrasses evolved during the age of the dinosaurs,
nearly a hundred million years ago, and are
found today in bays and estuaries around the
globe.
In shallow tropical and subtropical waters
these ‘prairies of the sea’ link the offshore
coral reefs with coastal mangrove forests.
They provide food and shelter for many marine
species that will one day inhabit the reefs.
Seagrasses and mangroves stabilize coastal
sediments and create buffers against storm
surge and flooding.
They remove carbon dioxide from the atmosphere,
filter contaminants from coastal waters, and
add value to local economies.
But seagrasses are in decline globally…
and mangroves are being lost to coastal development.
These areas are degrading right now, it’s
not 50 years from now, or a hundred years
from now, but it’s occurring right now.
The rate at which we’re losing seagrass
habitat globally could result in an ecosystem
collapse from the bottom of the food chain
all the way up.
Will restoring seagrass and mangrove communities
help sustain the ecological and economic values
of the ocean’s bays and estuaries?
And how will rising sea levels impact their
survival in the future?
Major funding for this program was provided
by The Batchelor Foundation, encouraging people
to preserve and protect America’s underwater
resources.
Over the last few decades, worldwide human
populations have increased dramatically along
coastlines.
At the same time, seagrasses have declined
at a rate of nearly 7% per year – a rate
higher than the loss of coral reefs or tropical
rain forests.
Storm water runoff from coastal communities
and human activities along the shoreline contribute
to the decline.
Boat groundings and anchor damage add to the
problem.
Unlike the more recognizable icons of the
seas, the value of seagrasses and mangroves
can be easily overlooked.
If you just casually read newspapers in places
that science stories are published you often
read about tropical forests, you often read
about coral reefs and occasionally you’ll
even read about mangroves, but you almost
never read about seagrasses.
Seagrasses are the Rodney Dangerfield of coastal
marine ecosystems.
They really get no respect.
But, researchers have discovered that seagrasses
and mangroves deserve a great deal of respect
for their many values in the ocean.
Seagrasses keep erosion down, they lock sediments
into the bottom and they actually remove sediments
from the water column.
When that happens it maintains a clear water
column so a lot of light reaches the bottom.
If seagrasses were to disappear then all of
a sudden they’re no longer holding these
sediments in place, sediments get up in the
water and the water becomes very, very turbid.
That’s really important when you’re thinking
about areas that are heavily populated, where
folks like to recreate where sediments can
get stirred up, they root them down and keep
them stable.
And they provide some hurricane protection
which, like mangroves do on a global scale,
you’ve got seagrasses and mangroves that
break wave action when storms come and that
also provide nature’s way of stabilizing
the shoreline.
We live in an area of the world where we get
these catastrophic storm events, hurricanes
and tropical storms and where they hit the
coast they can definitely create erosion problems.
And what we find is that areas that are protected,
or buffered by mangrove forested wetlands
tend to do much better.
And then we lose a lot of coastline in areas
where we removed mangroves and replaced them
with things like seawalls.
Still, some of the most important values of
these resources are less obvious.
It’s been shown that about a hectare of
seagrass, which is equivalent to a soccer
field, can use the same amount of nitrogen
that would come from treated sewage from 800
people in one year.
And then if you’re looking at the carbon
numbers, seagrass can fix the same amount
of carbon per meter squared in a year that
you would produce by driving your car 7500
miles.
Just the amount of nitrogen they pick up is
worth $19,000 dollars a year for that one
little spot of seagrass.
And you start to look at everything else that's associated with them, your not talking a monetary
amount for fisheries because you’ve got
the shrimp industry down here in South Florida,
you’ve got all of the sports fishing, as
well as most of the fish from either the mangroves
or the coral reefs having some sort of connection
with seagrass.
Seagrasses and mangroves provide the nursery
habitat, the foundation of our ecosystem and
without having a healthy nursery habitat where
fishery industries can survive and our tourism
industry thrives because we’ve got this
industry that depends on having nice clear
water and habitat where fish can grow both
for sustainability and sustenance for people
to eat and also for our tourism industry where
people like to recreate.
From the basic part of that food chain up
through human consumption you’d have, really,
an ecosystem collapse.
It certainly is a crisis.
Seagrasses are very valuable for the ecosystem
services they provide besides being just hot
spots of biodiversity and beautiful places
to visit.
I’m fascinated by seagrass habitats.
On the surface you look at a seagrass habitat
and you see a bunch of green grass essentially
that doesn’t look too different from your
lawn, for example.
But seagrasses, or the habitats are incredibly
complex, there are so many different organisms
that live there, there are so many different
bio-geochemical cycles and processes that
are going on in there.
If you put your face up close to a seagrass
habitat you’ll be amazed at the number of
different things that you’ll see on the
small scale.
In the sub-tropical waters of Southeast Florida,
neighboring metropolitan Miami, Biscayne Bay
Aquatic Preserve manages nearly seventy thousand
acres of submerged land.
Nearly three-quarters of that is covered by
seagrass.
Mangrove forested islands and shorelines grow
adjacent to these seagrass communities.
The most common variety, red mangroves, are
found growing at the water’s edge; behind
them, black mangroves; and farther upland,
white mangroves.
Historically, Biscayne Bay received freshwater
from the Everglades, but in modern times the
hydrology has been altered by drainage canals,
channelized rivers, and changes in the flow
of ground water into the bay.
The diversity of species has also changed
but it still remains an estuary where freshwater
and saltwater meet.
One of the things that we do is form partnerships
with local resource agencies, universities,
researchers who are looking at what the resources
are in Biscayne Bay so that we can get a better
understanding of what’s there now, but also,
how have things changed and how are they changing?
Marine biologists are monitoring salinity,
sediments and organisms that live on seagrasses
found in Biscayne Bay with a long term goal
of determining what effect a new freshwater
canal flowing into the bay will have on the
ecosystem.
This project is directly related to the Everglades
Restoration Project.
And what’s going to be happening is the
freshwater regime of South Florida is going
to be changing.
And everybody that’s involved wants to try to
get an idea of what and how these changes
are going to be affecting what’s already
here.
Overall, if you have salinities changing on
a much larger scale then you start getting
into chemistry a lot more, how warmer waters
are going to be acidifying with higher levels
of CO2.
That’s going to be affecting how the sediments
actually work, or don’t work.
It starts to get pretty ugly pretty quick.
We don’t know exactly what’s going to
happen.
Photo-archival data of the seagrass beds is
recorded with a specially designed boat and
shallow water positioning system known as
SWaPS.
We’ve got a glass bottom boat so you can
see the stuff that’s out there.
We’ve got a digital camera attached to the
glass bottom.
We can move that around as we need to.
That runs directly through a computer, goes
straight to a hard drive.
We’ve got GPS so it codes every photo with
exactly where it is.
Even if we’re doing a straight line, or
just trying to sit in one spot, each one of
these is tagged so precisely that we can follow
it around because seagrass doesn’t grow
all the time as just one big meadow like your
yard, there’s going to be little patches
of it.
This gives us a nice snapshot of the community
as it is right up against the mangroves and
how that changes as it moves into a little
bit deeper water.
We’re going out and year after year taking
photo quadrants, basically, and so that way in the
future we can always come back if we need
to check for any specific organisms or any
specific changes that we may have missed on
our preliminary analysis.
Seagrass and mangrove communities in Biscayne
Bay nurture juvenile fish and marine creatures
that feed and find shelter here.
Some will make their way offshore to the coral
reefs others will live out their entire life
cycles in the bay.
More than a hundred bottlenose dolphins reside
in the bay stalking fish around the seagrass
beds.
Seagrasses are a primary food source for manatees,
but as opportunistic feeders they will consume
low hanging mangrove leaves.
Seagrasses in tropical and subtropical bays
and estuaries around the world have a relationship
with mangroves like prairies do to forests
on land.
A good example of this is along the mangrove
fringe down in the southern part of the aquatic
preserve near Chicken Key and the Deering
Estate.
You’ve got an expansive mangrove forest
right adjacent to the shoreline and then out
from that for a few miles you’ve got dense
seagrass beds.
The prop roots of mangrove trees supply food
and shelter to some of the same marine organisms
and fish that are found in seagrass beds.
Because many near shore and offshore species
rely on mangroves as a nursery, when mangrove
habitat is lost fisheries soon decline.
Human impacts on these ecosystems are a clear
challenge for resource managers.
In the 1960s, developers acquired a section
of shoreline in the northern tributary of
the bay and cleared the mangrove forest to
dredge and build a marina.
Years later, the site was acquired to form
a part of the Oleta River State Park.
Today, it’s being restored to its natural
condition as a mangrove wetland.
This is a red mangrove propagule that has
just started to put out some roots and some
leaves, as you can see they are about 6 to
sometimes 9 inches in length and they come
off the tree as a very cigar-shaped, some
people say it’s pencil-shaped, very long
sort of propagule seed and they float in the
system until they find some substrate, and
the one end is a little bit heavier than the
other end and it tends to take root and get
in an upright position.
And again you have to remember the water is
going up and down as this is all happening.
Then once it starts to establish some root
into the substrate it will start to grow and
the mangroves grow about 2 feet a year.
They differ from one location to the other,
but that’s a pretty good average.
The red mangroves will grow up to a hundred
and fifty feet if they didn’t have impacts
as far as storm impacts.
And in this area we see them eighty to
a hundred feet tall. Unfortunately, we have
our frequency of hurricanes here is great
and as a result our mangroves are not as tall
as some of the ones in Southeast Asia where
they have a lower frequency of storm events.
These channel ways feeding into the site were
designed minus three feet.
It’s really been exciting in our restoration
plans, we not only just have a plane of mangroves
but we also have these tidal creeks and channels
and tidal pools.
And it’s amazing to see the life, the abundance
of life that comes in and it succeeds through
time.
We’ve seen fisheries that have come into
areas and just the species richness, or the
number of different types of fish or crabs
or shrimp have just gone right off the graph
as far as the number of individuals and the
diversity, the different types that come into
an area once it gets established.
My biggest thrill about all of this is pretty
much at a stage that we’re at now with this
project here where we’re pretty much concluding
the construction, we’re starting to plant
the site with volunteers, and that’s another
big part of this effort is to try to get the community
in to obtain a sense of ownership, stewardship
with the project, and families come out and
can plant these mangroves, and
come back and see the abundance of life
and what they’ve done and feel a part of
the overall restoration.
But balancing resource management and restoration
with recreational use is a steady challenge
particularly for specialists in Biscayne National
Park located at the southern end of the bay.
It’s a shallow water environment with submerged
resources like seagrasses and coral reefs
- a popular recreational area, but one that’s
frequently impacted by boat groundings and
propeller scarring.
We’re trying to put the sediment back in
the holes, or the scars themselves.
Seagrasses cannot grow well into the water column
itself, they need sediment to grow in, so
until we replace that, those injuries take
years and years and years to recover, if at
all.
We’re putting in sediment that’s very
fine and it can cause a very large turbidity
bloom in the water which is not a good thing.
We’re actually required through state water
quality standards to control that turbidity
very carefully.
So we will put up the yellow construction
boom around the site that we’re going to
be working at and make sure that there is
really very little option for leaking.
Then we’ll bring the sediment in on barges.
Sometimes we used containerized sediment,
for example in a burlap bag.
Sometimes we put the sediment that’s loose.
We use a crane, some kind of crane to actually
put it in the hole.
We have divers in the water feeling out the
surface with their feet to figure out where
we need to put more so we can place the sediment
exactly where it needs to be.
And the other thing the divers are doing is
collecting water samples for turbidity monitoring.
In the final phase of this restoration healthy
seagrasses will be transplanted to the site
– a method having great success in the Channel
Islands National Park off the coast of southern
California.
Alright, I’m in.
The rich seagrass habitats of the Channel
Islands sustain an abundance of marine life
- offering food for some and shelter for others.
Some of its species are found nowhere else
in the world.
Here, resource managers are harvesting healthy
seagrasses to transplant in damaged areas.
This five-year old restoration project has
expanded the seagrass beds up to a mile away
adding new habitat for a diversity of species.
But, it takes an informed public to share
the responsibility for sustaining these ecosystems…
And resource managers want to engage people
as well as local governments in promoting
the best ways to enjoy the bays and estuaries
while protecting the resources.
On behalf of Miami-Dade County and this community
do hereby proclaim March 2010 as Seagrass
Awareness Month.
Very good.
But will human intervention be enough and
in time to make a difference?
One of the things that is at the forefront
of everyone’s mind is, we’re managing
these areas but what does that mean in twenty
five years, or fifty or a hundred years,
we’ll be, this will be underwater, this
island that we’re sitting on right now.
So it’s a quandary.
In Southwest Florida’s Ten Thousand Islands,
bottle-nose dolphins corral their prey in
one of the most productive mangrove estuaries
in the world.
From the air, the islands look much the same
as they have for thousands of years.
But today they are ground zero for researchers
trying to solve one of the great scientific
problems of the future – predicting sea
level rise.
At Rookery Bay National Estuarine Research
Reserve scientists are trying to determine
how changing seas will affect the Ten Thousand
Islands’ mangrove forests and low lying
coastline.
We know without a doubt that sea level rise
is increasing and it’s actually an accelerated
increase.
That puts communities in Southwest Florida
at risk, not just here in Southwest Florida,
but I would say particularly so here because
people live on Marco Island and Naples and
the surrounding areas are living in communities
in these built landscapes in a very low lying
elevation.
A lot of the mangroves we have around Rookery
Bay are actually growing on living oyster
reef, and if the water quality conditions
are good, and in most cases in Rookery Bay
that is the case, as the reef slowly expands,
then we can also see an expansion of mangroves
that occurs at the same time.
Oysters have a tendency to grow up at a certain
rate off of the sea floor and if those oyster reefs
are growing faster than sea level is going
up the oyster reefs become emergent, they
come out of the water and then they become areas
for recruitment for mangroves.
So what was an oyster reef becomes a mangrove
forested island and those mangrove forested
islands have snaking like shapes, dendritic
kinds of patterns, and it’s those islands
that give the Ten Thousand Islands their name.
Now that sea level rise has accelerated, that
rate of sea level rise is faster than oysters
can grow, so that balance will shift and has
already shifted and it’s quite possible,
I would venture to say likely, that the Ten
Thousand Islands will disappear given the
current rate of sea level rise, which will
completely change the configuration of the
coast and completely change the estuarine
ecology of the coast, because those Ten Thousand Islands
also serve as entrapments for fresh water
that create the brackish water that serves
as the nurseries, serves as the place for
seagrass development, serves as a place for
other oyster reef development, that’s all
likely to change.
Researchers are studying sediment samples
from the Ten Thousand Islands to determine
changes over time in the mangrove communities
as a consequence of sea level rise.
These sediments indicate a shoreward retreat
of Southwest Florida’s mangrove coastline.
They’re also finding evidence of salt water
intrusion in the freshwater marshes of the
Ten Thousand Islands National Wildlife Refuge.
Arrays of circular sub-tidal ponds have been
photographed from the air.
Patches of mangroves are taking root where
only freshwater plants once grew – another
sign of sea level rise.
Since humans have become industrialized, since
humans have been recording history in history
books, we’ve been around during times of
modest sea level rise rates.
And we have barrier islands and bays, and
Ten Thousand Islands, and Biscayne Bays and
Florida Bays.
Those are all there because a modest rate
of sea level rise has allowed those features
to develop.
Now, again we see that in the sediments over
the last 5,000 years.
Now flash forward to industrialized world
and climate change and enrichment of CO2 in
the atmosphere, there’s clearly a record
in those sediments that sea level is
accelerating.
Scientists project the retreat of Southwest
Florida’s coastline if sea level should
rise from its current level one meter at a
time up to an additional nine meters.
Projections for much, much faster sea rises in sea level
over the next hundred, or two hundred years
would suggest to us that the area we’re
standing in now will soon be under water,
so one may ask the question, why bother protecting
the seagrasses here if the coast is going
to migrate away from here?
One reason is because there always will be
a coast and seagrasses will continue to respond
and move shoreward as sea level goes up as
long as humans don’t armor the coast to
such a point that a wall is built around human
cities and they continue to go up as sea level
comes up.
But, how fast will these changes occur?
And will seagrasses and mangroves continue
to yield their many ecological and economic
values with the changing seas?
For today’s researchers, these questions
are part of an experiment-in-progress with
the answers waiting somewhere in the future.
Major funding for this program was provided
by The Batchelor Foundation, encouraging people
to preserve and protect America’s underwater
resources.
