12 Jan - The life of krill
RRS James Clark Ross Diary
Noon Position: 61° 28.9 S, 52° 45.5 W)
Distance Travelled since Grimsby: 18627.5 Nautical Miles
Air temperature @ Noon today: 1.6°C
Sea temperature @ Noon today : 0.1°C
Weather: Moderate/poor, NNE, 6, 983.1 mb
Cometh the hour, cometh the krill
Having loaded up with a full complement of biologists last week we are now getting down to serious wildlife hunting. Everywhere the JCR goes they are trying to catch anything that might be alive, count it, sex it and watch it while it grows. Fortunately it is mostly little jelly like things that can only be seen under a microscope but it's all fascinating stuff. Despite being at sea for a week we haven't really got very far as we keep stopping to remove any life from the ocean that we can find. We are now entering the second half of the Antarctic season and instead of rushing around to all the bases discharging boxes of cargo wherever we can, the JCR settles down for a few months of hard core science. Each cruise has a name and we have now started the 'biosciences cruise' also imaginatively named JR82. It is a 6 week adventure in and around the Scotia Sea. I'll try and keep you up to date with the science in some sort of understandable form. Basically it's mostly about the wonders of krill but more of that later.
We have been sailing back across the Drake Passage, passed by Elephant Island and continued down into Erebus and Terror gulf. We got quite close to the Danger Islands. Named by James Clark Ross on 27 December 1842, when concealed by heavy pack, they were only seen when his ships were almost upon them. Just over 161 years later we also encountered ice and as the nets cannot be used with so much ice in the water, turned north again towards the Scotia Sea. To see our passage chart click on the image below.
The world according to krill......
What do you know about krill?? To be honest all I knew was that whales eat them by the ton and they live in Antarctica. I had never seen or tasted one. They had a slightly abstract quality to them. Well all that is due to change over the next few weeks as the JCR is swarming with krill and krill experts. We are setting off on a big game krill hunt around the Scotia Sea for the next 6 weeks. I think I'm going to stop worrying and learn to love krill (I'm beginning to worry - Ed).
You are going to hear lots about these little shrimp-like crustaceans over the next few weeks so you'd better read the following overview....
- Krill is a Norwegian word for 'whale food'
- Krill are mysterious
- Krill mainly live in a very small area of Antarctica
- Krill live for up to 7-8 years and grow to be about 6cm long
- Krill need somewhere safe to mature and grow, a good supply of food to eat, to avoid predators and reproduce (much like everything else)
Why are krill important to anyone?
Krill are a key component of the foodweb of the Southern Ocean. Levels of krill impact higher predators. If krill numbers fall so do the predators and the price of fish goes up at home. Also the numbers of whales, albatrosses and fun little penguins are affected. So, krill are IMPORTANT!
What do we know about krill?
Lots and lots but the basics are:-
- 1. Krill eggs are laid around December and January around the Antarctic Peninsula during the Antarctic summer. They sink in the sea to over 500m below the surface and when the water is at the correct temperature (0°C) they begin to hatch and grow.
- 2. Since no light or food exists at 500m the larvae rise to the top 100m near the surface to eat the plants that grow there. This is a critical stage in survival and once they have found enough food the larvae spend the next year growing. During the winter they live under the sea ice and feed on algae living on it's undersurface.
- 3. The infant mortality of krill is appalling and over 90% can die at this stage! However the lucky few survivors continue to develop, find food and avoid being eaten themselves.
- 4. After the winter the larval krill moult into juvenile krill. They are tougher now, bigger and start eating phytoplankton in the water. By this stage they are about 2cm long and can swim. They then spend another winter under the ice until they are 2 years old and finally reach maturity.
Phew. Well done. You are now an expert in the life of krill so sit back and look at the iceberg of the week to recover!
If only krill were that simple. They are actually international crustaceans of mystery. Most krill are found in the SW Atlantic, in the Scotia Sea area. The fishermen know that, and return there year after year to trawl for krill at the Antarctic Peninsula and South Georgia. One riddle is how krill keep station in this food rich area and avoid getting spread around Antarctica by the strong current system which surrounds the continent (The Antarctic Circumpolar Current). Do the krill swim against the currents? Or do the krill indeed get washed out of this area, but then they just die of starvation?
There is one clue which may help. We know that adult krill are transported in the currents from the Antarctic Peninsula to South Georgia, but the baby ones do not arrive here. We want to test two hypotheses to explain the lack of larvae relative to adults at South Georgia:
- 1. They are more prone to food shortage in the Scotia Sea and so starve on the way across
- 2. The larval krill live deeper in the water than adults, where the currents are different and so they are swept further south.
As you can see there are many questions yet to be answered about krill. JR82 aims to answer some of these questions by investigating the......
FACTORS AFFECTING THE TRANSPORT AND SURVIVAL OF KRILL IN THE SOUTH SCOTIA SEA
The chief scientist, Angus Atkinson, is leading a team of scientists who are looking at a wide range of different factors that may help to explain what these mysterious yet important things called krill are doing. There are several methods that are going to be used on the cruise and these include:-
- 1. Oceanography looks at the movement of water in currents, fronts and the properties of that water. This may tell how how krill migrate in the Antarctic Circumpolar Current
- 2. Nutrients and primary production investigates the tiny plants that krill eats and how well the plants are growing
- 3. Krill themselves are caught and counted in different areas to see how the populations move
- 4. Krill are kept on board ship to find out how rapidly they are growing and how resistant they are to food shortage
- 5. Higher predators will be observed including fish, whales and seals
All the information will be gathered in a systematic way by sailing in a series of transects. These are straight lines containing specific points where experiments will be performed and data collected. This system will allow a representative sample to be taken in the areas of interest and therefore a good spatial representation. To see the transects please click on the map below.
So that is the plan for the next 6 gripping weeks on the good ship as we sail around the Scotia Sea. If you didn't understand all that (or couldn't be bothered to read it - Ed) then sit back and look at a lovely sunrise that we were privileged to see this week just south of Elephant Island.
There she blows!
Just to prove that we are not being distracted from the big picture here is one of the 4 humpback whales that came to say hello. These magnificent animals swam round the ship a few times, scratched their noses on the hull then gently sauntered off again. For the scientists on night shift this was an unforgettable sight while the rest of the ship slumbered on!
Coming up next week: XBTs, UORs, FRRFs, bongos, Argos, RMTs and Signy!!