The Relationship Between Seagrass, Nutrients, Algae and Herbivores

2 months ago
With funding from Oregon Sea Grant, Fiona Tomas Nash is studying how nutrients from agricultural runoff and oceanic upwelling impact the growth of ...

English subtitle

I study seagrasses, which
are marine plants that
form underwater forests.
Seagrasses create
habitat and provide
food for many organisms,
including waterfowl or baby
fish or oysters or crabs.
And those are important
for fisheries.
They're also important systems
because they produce oxygen,
and so they are important
for life on Earth.
And they also provide
coastal protection for us
because they
attenuate wave action.
Our research, which is
funded by Oregon Sea Grant,
aims to understand how nutrient
impacts that are often caused
by either agricultural runoff
or sewage or from upwelling --
the waters that come
from the deep sea --
will affect seagrass beds
along the Oregon coast.
And we also want to know
how the little grazers --
the little herbivores that live
on these seagrass ecosystems --
might help mitigate
negative effects
of this nutrient pollution.
I don't think there's
any more seagrass.
Nutrient pollution is one of
the main causes of seagrass loss
worldwide, and what happens
is that these fertilizers
from agriculture stimulate
the growth of algae that
can overgrow the
seagrass and kill it.
And so we're trying
to understand
if this is a problem in Oregon.
But when you have this
nutrient pollution,
you have this algae
that grow, but you also
have these little
grazers, what are
like little snails, sea
slugs, and other animals
that eat this algae.
And in Oregon, we don't know
which grazers are there,
which these animals
are there, how
many are there, what are they
eating, how much are they
So our first goal
for this project
is to basically understand who's
there, what are they eating,
and, therefore, if we have
an increase in nutrients,
can they help buffer
negative effects?
The results of our research
can benefit multiple agencies,
both at the state and
the federal level, that
deal with food production,
fisheries, and water quality.
The research involves
several different things.
One is actually going out in
the field at four estuaries --
so Coos, Yaquina,
Netarts, and Tillamook --
to quantify how much
seagrass there is
and which animals are there.
We're collecting
isopods, which are
one of the main
grazers of seagrass,
and they are like
long and green.
They really camouflage
with the seagrass leaves.
So what we've done is
we're doing experiments,
both in the field and in the
lab, where we add nutrients,
and we also manipulate
the presence or absence
of these animals to see how
these combinations of more
nutrients and different animals
can affect the amount of algae
that there is and, therefore,
the seagrass health.
So here we have the fertilizer
in a little satchel with poles,
and then we also have
this PVC with poles,
so it diffuses throughout.
And here, we have the same,
but without any fertilizer,
so the satchel is
empty, just to account
for any potential effects
that this structure could have
in our buckets, like
light intrusion or changes
in the water flow.
So we have these and
we'll put them in here.
And then these plants will be
receiving much higher levels
of nutrients, simulating
nutrient pollution,
and then we can see
how the plant responds
and how the grazers
also respond.
Another experiment
that we're setting up
is an experiment to
examine how these nutrients
and these grazers
can determine how
the natives and the invasive
seagrass interact together.
In Oregon and in
the West Coast, we
have the native seagrass,
which is called eelgrass,
but we also have an invasive
seagrass that came from Asia.
This invasive seagrass
is much smaller,
and it's faster grower.
It may be better at benefiting
from nutrient pollution
than the slower growing
native seagrass.
We want to look at how one
will outgrow, potentially,
or grow better in comparison to
the other, so how they compete
and how that changes when
we have nutrient pollution
and when we have these grazers.
We'll be doing
feeding trials that
try to see if the native
animals that we have
on the eelgrass beds
would eat the invasive
or the native seagrass, and
which one they will prefer,
and how much would they
eat of each of them.
So we can understand
whether there's
this potential for
the native animals
to potentially limit
some of the capacity
of this invasive
species to expand.
And so here we have
isopods that are being fed.
For example, this one is fed
an option of the two species,
so here's the invasive
and here's the native,
so it can feed on both.
This one just has
the native species,
and this one just has the
invasive one, for example.
It's a very large-scale
project and means
we have a lot of samples.
Without Oregon Department
of Fish and Wildlife,
without EPA, and
without South Slough,
we would not be able
to do this work.
Thankfully because of
this great team of people,
we're doing everything,
and I think --
I'm very proud.