January 6 2011
Well, first of all I just want to apologize if you had hoped for a new bigger, longer tank project with faster updates and bigger animals and more algae ;-). Like I said at the end of the last blog, this project will be a small test project. And most likely these pages will have even fewer and less regular updates. Even though it's been about 18 months since last time I kept an aquarium I certainly haven't been out of the hobby. Just looking at nature is a great part of the hobby to me. Last year I was both in Egypt, by the Red Sea, and in Thailand. Both places had great snorkeling opportunities. The Rea Sea with its crystal clear water made a great impression. I highly recommend that! I still haven't gotten around to snorkeling here in Norway. But we'll see if there is time this summer. I have also spent a lot of time planning this plankton project. I am so frustrated with the complete lack of ability to measure, or estimate, quantity of food available to filter feeders. I wanted to use more scientific methods to measure things, and know the numbers behind it all. So a lot of googling and reading was needed. Now I finally feel that I have enough theory and numbers in place to start up something. Also, there is no doubt that the 18 months break has gotton the fingers twitching with a need to do some practical stuff.
Kelp forest in Øygarden.
The first setup will be a test to try plankton growth. There will be 2 112 liters aquariums. One will be a plankton refugium, and the other will be a combined sump and specimen holding tank for filter animals. Another important function for it will be to act as a plankton sink. I want as little plankton as possible to go back to the refugium. This is because that is the most realistic setup in a heavily populated display tank with good skimming. Originally, the thought was that I could grow both phytoplankton and zooplankton in this refugium. I really did some background checking this time and gone into the theory behind it all. I considered various setups. Some with separate tanks for zoo- and phytoplankton. But I found the challenges around these two types of organisms far too great to try and handle at the same time. So first thing first; phytoplankton. I also wanted a complicated phytoplankton environment in my refugium, not just one species. But that may be too optimistic. I'll just have to try and see. I can set up something that produces a steady, high, flow of phytoplankton by reprocessing the nutrients in the system, then that should be good enough.
I have bought a little bit of equipment already. Here are the two 112 liters.
The first challenge with phytoplankters is seeing them. There is a great variety of them. Some species form colonies of various size and shapes, and some single cell "giants" can be as large as half a millimeter. These can be seen in a stereo microscope at 40 or 80 times magnification. On the pictures below you can see some dinoflagellates of the genus Ceratium that are very common here. It would be great to be able to grow these. But because of the way the refugium is set up, the most likely to make it will be the small ones. That means sizes of down to 2 micrometers. There are even smaller plankters than that too. So I bought a microscope of the "advanced hobbyist" type.
My new large microscope can magnify up to 400 times, or 1000 times with oil immersion. The stereo microscope can magnify 80 times with acceptable quality and 40 times with high quality. The pictures from the stereo microscope are way better since the object is lit from above on a dark background.
To measure size with the microscope a clever device called a stage micrometer is used. It is a glass slide with a scale on it. The scale is so tiny it can barely be seen with the naked eye, but in the microscope the 10 micrometer scale can clearly be seen. There are 100 of them on one millimeter.
400 times magnification lets me see an area of roughly 500 micrometers in diameter (0.5 mm).
Same magnification. As you can se the algae cell here is 20 micrometer in diameter. For reference, a human red blood cell is 6 to 8 micrometers, so it would fit well between two lines. The popular aquarium food algae Nannochloropsis has a diameter of 2 micrometers. Bacteria are typically 0.2 to 2 micrometers, so they would be visible as specs of about the same thickness of a line, or not visble at all.
I spent a lot of time trying to find ways to quantify the plankton. It would be really great if I could just take an amount of water and get to know the exact biomass in it. But that just doesn't seem to be possible. One thing I can do though is to use a hemacytometer to count the number of algae cells in a given volume of water. I haven't tried it yet, but if it works it will allow me to do things like estimate algal biomass, growth rate and quantitative species composition. A hemacytometer is a device that was made to count human blood cells in a known volume to get the concentration in the blood. It is a special slide with 3 ridges, as you can see on the second picture below. The middle ridge is exactly 0.1 mm lower than than the others. If you place a cover slip over them there is a volume between it and the middle ridge. On the ridge there is a grid of lines forming squares of known size. Because the height is known too the squares mark water volumes of known size. Counting cells in the volumes gives concentration of cells.
Looking carefully you can see that the middle ridge is 0.1 mm lower than the others.
Taken through the stereo microscope at 40x magnification. A large 6mm Calanus copepod. The green balls are characteristic Volvox algae colonies.
Calanus and cyclopoid copepods.
Various stuff from a plankton catch. Algae threads, copepods and ehm... blobs ;-).