How will the increased ultraviolet radiation from the hole in the Ozone layer affect the krill of the Southern Ocean?
Research scientist Stuart Newman investigated this question and discovered a remarkable story of natural adaption.
Krill are a 'keystone' species. (Image: Stuart Newman)
Krill are definitely worth
worrying about. They are thought to have the highest biomass of any
multi-cellular organism on Earth. They form the backbone of the southern
ocean ecosystem and are a "keystone" species. If the krill
were to disappear, all of the creatures which feed upon them would
In general, most animals bigger
than krill will eat it, from whales, seals, penguins, other seabirds
(Humans also fish for krill but so far we havenít quite figured
out what to do with them apart from use them as feed for fish farms.
As a result, the krill fishery harvests far less from the oceans
than it potentially could, but this will most likely change in the
At the other extreme, krill
will eat pretty much anything smaller that you put in their way, be
it diatoms, dinoflagellates, smaller zooplankton, algae living underneath
the ice, or even other krill. This "bottleneck" between
what krill eat and what eats krill makes anything that might affect
their numbers of huge importance to the rest of the ecosystem.
Factors that may affect their numbers include such things as global warming, sea ice area, competition with other species, possible over-fishing in the future, and of course the ozone hole.
Surprisingly, it is only recently that the possible effects of UV
on Antarctic krill have been examined in any detail.
in close-up. (Image: Uwe Kils, Rutgers University)
for full size pic
Because of this oversight,
Iíve been studying whether krill are affected by high UVB from the
ozone hole for the past 3 years, with colleagues at the Australian
Antarctic Division, and the School of Zoology/Institute of Antarctic
and Southern Ocean Studies at the University of Tasmania. In that
time weíve found some interesting things about how krill cope with
in the cold room of the Aurora Australis, tending the krill after
a successful trawl close-up. (Image: Stuart Newman)
However, my first finding
was somewhat alarming. I found that krill in captivity are remarkably
susceptible to UVB, which killed them in under a week. The levels
were quite low, similar to those seen at 5-15 metres down. Interestingly,
krill were not harmed by UVA, which is the "tanning" kind
of UV. Then a friend of mine revealed krill DNA to be more prone to
UV damage than any other animal yet examined and the story got more
But there was something
else going on out there in the oceans. If krill are so fragile around
quite low levels of UVB, how come there are so many of them in the
southern ocean? Itís certainly not because they stay deep and out
of the range of UVB Ė krill regularly haunt surface waters during
the day to feed and be fed upon. If they didnít there would be a lot
of anorexic penguins trying to get into fashion modeling.
So how do the krill deal
with all this? One possibility is that they simply go deeper, for
UVB gets weaker the deeper it goes. But to respond to something, you
have to be able to sense it. So I asked the question: can krill react
Krill behaving badly
After hours of watching
krill react to different strengths and gradients of UV radiation in
horizontal and vertical fish tanks, the short answer to whether they
react to UVB is:
No, they canít.
When put under UVB krill
behave as if nothing is happening when in fact they are slowly having
their cells, membranes and DNA damaged. This was a worry until we
tried UVA, and found that krill do indeed react to UVA by either swimming
away or going deeper. This is an interesting thing to be able to do,
but why would krill react to something (UVA) that doesnít hurt them?
Why waste effort?
krill catch (Image: Stuart Newman)
Possibly because of the
way the solar spectrum is. Where thereís UVB there will always be
UVA, as they sit next to each other on the spectrum. In fact, UVA
is always stronger than UVB, but because UVA has a longer wavelength
(320-400 nm compared to 280-320 nm), it has less energy and is therefore
less harmful than UVB. So when krill react to UVA and make a run for
it, they are indirectly reacting to invisible UVB.
The trouble with that is,
the ozone hole doesnít affect how much UVA gets through, only UVB.
So if krill are swimming away from levels of UVA to which they have
adapted, itís possible that when the ozone hole happens in spring,
they may be getting a nasty dose of UVB without even knowing it.
To make things worse for
the krill, sometimes running away isnít enough. They often need to
get close to the surface to feed, mate, and do all the things that
make being a krill worth the unending threat of being eaten by a penguin
or caught in a net by the likes of me.
scream (You scream we all scream) for sunscreen
So sometimes krill just
have to cope with it. Luckily they can do this by using their own
built-in sunscreens, or if you prefer, their high concentrations of
"mycosporine-like amino acids." This isnít news Ė weíve
known for a while that algae and fungi can make their own sunscreens
in the form of mycosporine-like amino acids (MAAs), which absorb very
well in the UV and are produced in response to it. MAAs are very common
in marine species, especially so in tropical coral reefs and the Antarctic,
two areas which are routinely savaged by high UVB.
& white line drawing of a krill (Image: Stuart Newman)
Algae are especially good
producers of MAAs, and it is from the algae that krill can acquire
their sunscreens, although it seems that some sunscreens are taken
up more readily than others. This means that krill can "piggy-back"
on algaeís natural response to high UV: when UVB is at its highest,
the algae produce high concentrations of sunscreen, the krill eat
them, and survive UV better than krill low in MAAs.
And If the ozone hole gets
worse, krill will be prepared, as when UV increases, algae will make
more sunscreens, krill eat them, take up more sunscreens and are further
But it doesnít stop there.
Once inside, the sunscreens tend to head towards the vulnerable eyes
of the krill. Krill eyes have the highest concentrations of sunscreens
anywhere in their body, and we think this provides protection for
So what's the story?
Thatís a lot of adaptations.
So lets follow this through from the sun to the krill.
Krill are highly susceptible
to high UVB, especially their genes;
However, krill can sense
high levels of UVA and increase their depth to avoid it;
But the ozone hole lets
through more UVB relative to UVA, further threatening the krill;
Happily, krill possess
high concentrations of natural sunscreens in their tissues, which
offer some protection from high UVB.
So, for a beast that looks
disarmingly like a prawnís sissy younger brother, krill are remarkably
well adapted to the high UV that the southern ocean experiences thanks
to the spring ozone hole. They also rather rudely show up how badly
designed human beings are, for our usual response to high UV is to
head for the sunscreen bottle or the nearest umbrella.
Krill are immune to such
nonsense. So while the scientists and politicians frantically try
and fix the ozone hole with treaties and protocols, the krill are
sitting pretty, perfectly adapted to their environment.
And I cannot help but applaud
them. But right now Iím off to find some shade.