I'm going to move straight to our next speaker which is Dr Leonie Suter
who is going to talk to us on using environmental DNA to survey Antarctic krill.
Leonie completed her PhD in Switzerland, studying how plants can adapt to a changing climate.
She then sailed on a small yacht from the high Arctic to the Caribbean for two years with her husband
and her dog and ended up studying the sex life of Antarctic krill in Tasmania. What a journey!
Leonie's current work focuses on how we can detect life in the Southern Ocean
using environmental DNA, highly topical area.
Thanks Leonie.
Thank you
So I'll jump straight in.
What is environmental DNA?
Well, environmental DNA is the DNA that's released by any organism, at any time, into any environment.
In the case of Antarctic krill that might be molds or faeces or eggs or any dead decaying
tissue that's released into the environment and then spreads in that environment.
Now any other organism in the marine environment is doing the same thing so that we end up with a
soup of DNA of all the surrounding organisms in the water in every litre of seawater.
We can access that information by taking a small water sample from the environment
and that can be done, for example, from directly from a ship or anywhere we really can get to
from under sea ice or even from the deep sea and this information can then be used to describe
communities, community compositions, species distribution, how species interact with each other
and over time we can monitor the response of these species and communities to change and importantly
we can do that without ever having seen any of these species in person, so to say, we just use
the traces they leave behind, the DNA signatures.
Now we can describe whole communities but we can also zoom in and look at single species in more
detail and that's what we've been doing here.
I don't really need to say anymore "why krill?" I think you've heard enough about why krill,
it's an incredibly important keystone species in the Southern Ocean, really abundant and a lot of
predators depend on it.
It's also targeted by the krill fisheries and for the sustainable management of the krill fisheries, we need to know how
much krill there is and what its distribution is.
You've already seen about the the amazing tools we have for acoustic surveys,
we also use troll surveys to answer these questions but here we investigated
whether eDNA based methods can be additional tools to survey
where Antarctic krill can be found and get insights about their habitat use and abundance.
Let me go back one. What we don't know about eDNA in the Southern Ocean is really for how
long it sticks around so once it's been released into the environment the DNA
strings actually begin to break and they get smaller and smaller and more fragmented and
once they're really short we can't really tell who it belongs to anymore so there's a
limit to for how long we can detect it but we don't really understand what that is.
To understand more about that we set up an experiment in the krill lab at the AAD in Kingston
and we put some krill into some small tanks and we let them release their eDNA into those tanks
for two days and then we removed the krill and resampled those tanks for two weeks
to see how the eDNA of krill decays over that time and we did our genetic tests and in fact we used
genetic markers of different lengths to not only see how the DNA might decay over time
but also whether it fragments more over time so we can get an idea for
how long the eDNA's been floating around and this is what we found.
So you can see that over the course of these 14 days the DNA degrades quite rapidly
but also so we have these three different length markers over the course of these two weeks the
DNA begins begins to fragment more and more so based on this fragmentation we then get
an idea of whether the eDNA has been released recently into the environment or has been floating
around for a longer time which will help us to interpret the data we're actually collecting.
We've then taken this method to the field. This is a resupply voyage to Davis station where on the
way back we collected small water samples all the way to Hobart and we measured the Antarctic krill
DNA from Davis station to Hobart and the size of those circles indicate how much we actually
found for each location but we can also get an idea now how fresh or old this eDNA is.
So the white ones contain eDNA that's less fragmented whereas the dark ones contain
more fragmented eDNA so it's probably been floating around for a longer time.
This is just one of the markers we can use to get information out of these samples.
We can also target other species. For example, we used a marker that can detect mammals
and in the very same samples we found a whole range of whale and seal species so depending
on what you're interested in you can target your markers and find really anything you like.
The next steps are going to be to actually investigate areas that are usually a lot more
difficult to survey. For example, we know that krill are using the deep sea occasionally,
probably, as a habitat but we don't really know how often, how wide spread
we've got samples from the deep sea that we can use with this method to
see whether they're commonly found there or whether it's just every now and then.
We want to compare this new method to already existing methods to understand better what this
data actually means and then we want to use a whole range of additional markers such as
markers targeting predator eDNA or overall animal communities
to understand better how krill fits into the Southern Ocean ecosystem.
That's it.
Thank you.