30 January, 2003
I made krill pellets in the lab today. Tasty, tasty if you are a sea star in Antarctica! How do you make a krill pellet? Well, seawater is heated and stirred until it is barely bubbling. Stir vigorously, creating a deep vortex (it will look like a tornado). Since this is not your mother's kitchen, the faster and splashier you stir, the better! V-E-R-Y slowly stir in alginate. Drop the alginate directly into the center of the vortex S-L-O-W-L-Y continuing to stir. Use a glass rod to break up any chucks of alginate that formed, but if the alginate was poured in slowly enough, you may not have any chucks. Yea! Allow the solution to cool to room temperature. With the glass rod, stir in ground krill powder. Cut the tip off of a large pipetter (it appears to look like a huge syringe). Put the mixture into the pipetter. Drip the mixture into CaCl2, one drop at a time. Take a pair of forceps and carefully lift the pellets from the CaCl2 and place them on a paper towel to dry.
Alginic acid is a type of polysaccharide. Starch is a polysaccharide, a polymer of many sugar (glucose) molecules linked together. Alginic acid or alginates are long polymers of two types of sugar-like molecules. Alginic acid is found only in brown algae like kelp, the source of the powder we were using in the lab. Along with cellulose (aka fiber), algin is found in the cell walls of brown algae. It therefore serves structural function in these algae.
CaCl2 is Calcium Chloride. A molecule of Calcium Chloride has one atom of Calcium and 2 atoms of Chloride. When a solution of alginate is exposed to CaCl2, the calcium cross links the algin and in a process called polymerization (poly meaning many, mer meaning units) makes the liquid algin solidify.
What's so special about a krill pellet? Part of the research being conducted examines whether or not certain organisms are palatable to sea stars. Those that are rejects are tested for their chemical composition to see whether or not there is something in their chemical composition that makes that organism unpalatable to sea stars. In Antarctica, the scientists will be diving to the sea floor to collect sea star samples. The sea stars will be placed in an aquarium in the lab. The sea stars climb up the sides of the aquarium, "stretching" out their arms. The researchers put a little pellet of food about halfway up the sea star's arm. Sea stars have taste sensors in their arms. Their mouth and stomach are located on the underside of the center of the sea star. If food is tasty to the sea stars, the pellet will be moved toward their mouths and they will eat it. The sea stars will move food that is unpalatable down the arm so it will fall into the water. Chuck says if it is really nasty, they will "flick" it off of their arm straightway. Most sea stars appear to like krill, so the scientists make up krill pellets as a control in their experiments. What that means is the scientists will experiment with the sea stars and offer them a list of treats to see which ones the sea stars accept and which ones they reject. After a couple of different samples, the scientists will offer the sea stars a krill pellet knowing most likely that they will choose to eat that. Once in a while, a sea star will reject everything that it is offered. Then the researcher gives it a krill pellet to see if the sea star really does not like anything offered it or if it is just being finicky. The organisms that the sea stars reject are tested for chemical composition to see what is in the chemical make-up of that organism that keeps it from being preyed upon by sea stars.
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