I'm here to unveil a new
carbon-removal technology,
one out of sight and uncelebrated.
Meet our champion: seagrass.
A very unlikely champion,
but yet a remarkable power
of carbon removal.
Seagrasses occupy
only 0.1 percent of the seafloor,
but they remove one-third
of all of the carbon
that gets sequestered
in the seafloor annually.
They are no ordinary seagrasses,
and yet, we didn’t know much about them.
When I started my journey
of research and science with seagrasses
about four decades ago,
we knew that they were flowering plants
that had adapted to grow
and colonize the ocean,
but we didn’t know
how amazing the adaptation [were] required
to [be to] achieve this feat.
In fact, only seven years ago,
we published the first
genome sequence of a seagrass,
and we were mesmerized at the amazing
adaptations that were required
to be able to colonize the ocean.
And now we understand why only 17 species
from among 300,000 or so
species of flowering plants
that are present in the biosphere
have conquered the ocean.
Seagrasses grow by extending a rhizome --
that is a subterranean stem
that elongates at rates
of about one centimeter
to about five meters per year,
and they branch
and extend along the seafloor,
forming large clones.
We knew that clones can be quite large,
but we were surprised
when, in the Mediterranean,
we found, 10 years ago,
a clone that occupied 15 kilometers;
that is the size
of the island of Manhattan.
And this is a very remarkable clone,
but we also calculated that the seed
that gave rise to this clone
germinated in the seafloor
200,000 years ago.
This is one of the oldest
living things on the planet,
and the meadow
where this megaclone is growing
is now recognized as a marine
World Heritage site.
Off the island of Ibiza,
this meadow occupies
about 800 square kilometers
and is now recognized as a protected area,
not just because of the long
life span of the clones
but also because
of the biodiversity it supports.
But we also found that this meadow
is also the champion of carbon
sequestration in the biosphere,
with one hectare of this seagrass
sequestering as much carbon
as 15 hectares
of pristine Amazonian forest.
Finding [out] how this is possible
was a path of discovery.
First, the canopies
of these plants are very large,
and they are among the most productive
ecosystems on Earth,
pumping carbon dioxide
into organic matter at amazing rates,
that produce a lot of carbon,
much of that being
sequestered in the soils
as rhizomes and roots
that are very hard to decompose.
The large canopies also form a web
that dissipates energy
and filters out particles from the flow
that settle, then, in the seafloor,
protected from being resuspended
by the protective cover of the canopy.
And these particles in the seafloor
decompose very slowly,
because the seafloor
and the soils of seagrasses
are devoid of oxygen,
and that slows down
microbial decomposition.
So this carbon accumulates
and is preserved in the soils.
And there's one more reason
why these seagrass meadows
are so effective at sequestering carbon.
And it’s that, unlike forests,
where carbon in the soil
gets emitted back to the atmosphere
with wild forest fires --
which, unfortunately, are becoming
more frequent with climate change --
there are no fires underwater,
so the carbon that settles in the soils
of seagrass is safe
and accumulates
over thousands of years, safely.
In fact, seagrasses not only grow
along the seafloor --
they also raise the seafloor upwards
at rates of one to four
millimeters per year,
and they do so,
over centennial timescales,
to the point that these
seagrasses form reefs,
such as this four-meter-tall
reef of seagrass peat
that is found in the Mediterranean.
And this is not the tallest seagrass reef
that has been discovered.
My colleagues have dug out a seagrass reef
that is 12 meters tall,
three times this size.
Just imagine the amazing amount of carbon
that is being held
in these seagrass reefs.
But it is not only carbon.
The seagrass reef protects the shorelines,
protects our infrastructure,
protects our property
and protects our lives.
And this protection
becomes particularly important
at a time when climate change
is raising sea levels
and is also leading to increasingly
strong storms and cyclones.
So very often,
seagrasses form the first line
of defense for the shorelines.
So as we became aware
of the important role of seagrass
in carbon sequestration,
and also in defending our shorelines,
then we were almost too late
to benefit from those protections,
because, sadly, we had lost
a lot of seagrass in the ocean.
In the 1930s,
disease wiped out seagrass
along both sides of the Atlantic.
And as they were starting to recover,
sewage input and agricultural runoff
led to mortality of seagrass
along the shores of all continents,
and that was aggravated further
with mechanical damage,
such as the dragging of this anchor
from a megayacht in the Mediterranean
that is plowing away
this millenary seagrass,
exposing the sediment and resuspending it
so that it will be emitted back
into the atmosphere as carbon dioxide.
And that was compounded with dredging,
trawling and coastal works
that impacted seagrass.
So by the end of the 20th century,
we calculated that one-third
of the known seagrass areas in the ocean
had been lost.
And yet efforts to protect them
became urgent.
But we can only protect what we know,
and our knowledge of the distribution
and area of seagrasses in the ocean
is still very poor.
Our estimates range
between 150,000 square kilometers
to one million square kilometers.
And narrowing down this uncertainty
is very, very challenging.
In fact, it can only be done
by scuba divers,
because seagrass meadows
cannot be resolved from satellites
or from airborne sensors,
because the deeper parts
cannot be differentiated
from other types of grounds and seafloors.
So we are actually partnering
with much better swimmers than we are,
but that share our interest
in seagrass meadows.
We are partnering
with green sea turtles,
which are mostly feeding on seagrasses,
so we track them with satellite devices
to find out where
their feeding grounds are,
and by doing this,
we are finding and discovering
new seagrass meadows
in the Indian Ocean and the Red Sea,
which were poorly studied.
And in the Bahamas,
we are now partnering with tiger sharks,
because we found that in the Bahamas,
tiger sharks spend
about 70 percent of their time
cruising over seagrass meadows.
And we instrumented,
last year, for the first time,
a tiger shark with 360-degree cameras,
which are sitting on the fin of the shark
so that when the cameras
pop up to the surface,
then we retrieve the footage,
and we can ascertain in which areas
of the track there were seagrasses.
So using tiger sharks as partners,
we have now discovered
that the Bahamas' banks --
which a US astronaut, Scott Kelly,
deemed to be the most beautiful
sight from space
when he shared this photo
that he took from space --
is actually the largest
seagrass meadow in the ocean.
And we are now growing policies
to protect seagrasses
and improve water quality
so that we can recover seagrasses.
And I tell you what,
these policies are working.
And over the last two decades,
we have seen a rebound of seagrasses
following almost a century
of sustained decline.
Now seagrasses are starting
to expand and recover
along the shores of Europe, North America,
Japan, Australia and China.
And this is only the beginning,
because we can do more
than just protect seagrasses
and wait for them to come back.
We can engage in active restoration,
such as my colleagues
in Virginia have done.
And in the early years of this century,
they released 7.5 million seeds
of seagrasses in South Bay,
in the coastal waters of Virginia.
And 16 years later,
the seagrass has expanded
to 20 square kilometers,
and by now it has covered,
already 36 square kilometers.
The amount of carbon that this restored
seagrass meadow has trapped
is so important that it has led
the Commonwealth of Virginia,
that owns these waters,
to pass a bill that regulates
how carbon grades
from seagrass restoration
should be reinvested back
in further restoration of seagrass,
and also in improving our understanding
of seagrass ecology.
But seagrasses are more than just carbon.
They also have seeds,
and my friend and three-star
Michelin chef, Ángel León,
has released this year
an important development,
which is that these seeds
can be consumed by humans
as marine rice.
And this is a wonderful crop,
one that does not require
arable land, fresh water,
neither fertilizers
nor herbicides or pesticides.
And because we only need to clip
the flower and shoots where the seeds are,
we don't need to harvest the plant,
so the meadow continues
to sequester carbon,
promote biodiversity
and defend our shorelines.
And these findings, in the past decade,
have made me believe
that it's time to ditch the idea
that seagrasses are the ugly ducklings
of environmental conservation,
as I nicknamed them 15 years ago,
frustrated, because at that point,
not even conservation NGOs cared.
Now we know that seagrasses
are beautiful swans --
which actually eat
seagrass leaves and rhizomes --
and healthy seagrass meadows
are harbingers of a healthy ocean.
And I am inspired by the tide change
from a century of loss of seagrass
to two decades of recovery
to imagine that we can actually do better.
We can expand this success story
to the rest of marine life,
and last year, we published a paper
in the journal "Nature,"
where we pledged
that it's possible to recover
and rebuild the abundance of life
in the ocean by 2050.
Just imagine that it is within our [grasp]
to hand over a healthy ocean
to our children and grandchildren.
And as we do so,
we can also step up in our race
to stabilize our climate.
Thank you.
(Cheers and applause)