8 February, 1998
We have really stepped up the pace these last two days, doing 4 stations a day rather than the three we were doing before. At each full station, we have several operations that go on in sequence. First the plankton nets are deployed. When they come up, the PRR is run. When all that equipment is back on board, the CTD goes down. Several groups take water from the CTD, so it must be last when all of the groups can access it.
The plankton nets are mainly to catch krill. Krill are small, shrimp-like crustaceans that are found in these cold Antarctic waters. They are similar in function to the small fish, such as sardines and anchovies, found in more temperate waters. Krill swim in schools and spawn, possibly as much as twice a year, by releasing a great many eggs into the water column. It is not really known yet whether krill move as school through the water by actual swim behavior, or if they are just passively moved by current.
Dr. Langdon Quetin has been studying krill since 1981. He received his doctorate from UCSB in 1979. He is currently the PI on board for the krill studies, but actually he is a co-PI on this and all his proposals. His wife, Robin Ross Quetin, who isn't along for this cruise, and he have been co-PIs since 1981 when they started working in Antarctica. The hypothesis for this investigation on krill is that krill are food limited and that the sea ice sets up conditions for krill reproduction success. For there to be adequate food for egg production, there must be spring blooms of ice algae and high levels of summer phytoplankton. The sea ice holds the phytoplankton up near the surface, making it more productive and ready to produce blooms. Krill are essentially grazers, like cows or buffalo, and the phytoplankton serve as their prairie. In years where there is little grass, the grazers are stressed physically and do not produce as many offspring. The same thing happens with the krill in years that there is little sea ice, therefore little phytoplankton.
According to Langdon, krill can live 5 - 7 years. Although it is hard to determine krill age, it has been done by a fluorometric technique that reads an age pigment in cells. It takes about a year to a year and a half before krill are big enough to really be whale or penguin food. So, if there is a low algae year, it may take a while for it to impact the other organisms in the food chain. This has been a low plant growth year so far, and the reproduction rates of krill have not been great.
They also run into salps that, as Langdon believes, are probably products of the different water mass systems that push in and out of the continental shelf area or, as another has proposed, they may be a competitor of krill. Salps are not a favorite of those who study krill because if there are many salps, there are few krill as Doug Conlin, who works for Dr. Quetin, added. Salps look something like a jellyfish, but they are much more complex and have an interesting way of collecting food. Internally, salps have a screen that filters food from the water that is pumped through their body If there is too much food, the screen becomes clogged and the salp rolls the screen up, ejects it, and forms a new screen. Neat, huh?
Well, I need to get back to the lab and test another set of dissolved oxygen samples form the CTD sampling. There will be four sets of 11 samples plus other sets taken from my testing and random surface water samples. I will be busy this evening!
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