December 1 2011
Last month was devoted to the ongoing zooplankton experiment. I restarted the refugium, this time with a net in front of the overflow to prevent large zooplankters to pass. After a week the usual diatoms were in full bloom. I then introduced a good catch of copepods, and a few mysids. The copepods were calanoids. I was lucky to find a presentation on the web that showed development times for Calanus finmarchicus, one of the most common species of calanoid around here. It showed a great chart over growth times for all the stages at various temperatures. The highest temperature shown was 12 degrees which is much lower than my refugium's 19 degrees. I assumed that the copepods would grow that fast or faster. The chart showed that the time from egg to adult was 30 days at 12 degrees and 21 days to stage C5 which is the second last stage. So logically, if I could see small specimens in the refugium after 3 weeks those would have to be born in the refugium, given the copepods could maintain max growth rate. If I could get them to breed in the refugium there was a good chance of getting a growing population established. According to another paper, Calanus finmarchicus could live at temperatures up to 22 degrees. Temperatures above 20 C were harmful, and 24 C was deadly. So 19 could be just within the acceptable limits. But ideally it should be much lower. Continuous exposure to light was harmful. That could also be a problem.
These are calanoid copepods of about 2 mm body length photographed in a glass of water with a black sweather as a background.
I think it is a large infection of fungus or bacteria on this specimen. It could be a problem caused by warm water and high bio density. The specimens in these pictures had been living a little more than two weeks in the refugium.
One and a half week after having put copepods in the refugium I noticed that there were still many left, but I had the impression that a large portion of them had disappeared. I couldn't see any nauplii. I had also added some mysis shrips to the refugium, because I thought that these were also feeding on phytoplankton and may be able to lay eggs. The shrimps were probably of the species Praunus flexuosus. It turned out that these are not filter feeders on phytoplankton, but omnivores that prefer zooplankton like copepods. So it was pretty useless to continue the experiment when the refugium had a bunch of large predators. At this point I also took some samples of the copepods and looked at them in the microscope. If the copepods had grown at full rate all those that were copepodites at the time of capture should be at stage C5, the stage before diapause and adulthood by now. But judging by size, most seemed to be at earlier copepodite stages, indicating slow growth. Predators could not explain this issue. I came to the conclusion that it was no point to continuing with zooplankton until I had eliminated the temperature variable from the equation. There is a solution to my temperature problems that I have thought about all along, namely installing a "CoolWorks Ice Probe" chiller. This is a small, elegant 50 Watts Peltier effect chiller that is just stuck in through a hole in the side of the aquarium. It does not introduce any pumps to the system. My lighting over the refugium is 48 Watts, so it seemed reasonable that the Ice Probe would do the trick of getting it a few degrees colder. These chillers are made in the USA, and are not sold in Europe at all. So I had to order from Marine Depot in the US and pay more than $100 in transport costs. Two chillers are currently in shipment. Luckily they run on 12 Volt DC current. So I can use them here in Norway by replacing the 115V to 12V transformer that is included with a generic 230V to 12V transformer.
This mysid (Praunus flexuosus), eats copepods. Even though I don't believe it is the decisive factor, it could be a problem. They are about 2 cm long.
Lately I have not been adding CO2 to the refugium. Most of the time I haven't even been measuring pH. I can't really say that I have noticed a great difference in algal growth. So I want to continue experimenting with not dosing CO2. It would be a great advantage if I could avoid CO2. I love my little technical setup and my big CO2 tank. But it is a hopelessly unstable system. Still, when I get my new temperature regime I can't rule out trying it again.
I have been reading a little about these animals lately. They are truly interesting. I have always heard about how they are so important for life in the ocean. They are the primary food for important fish species like herring and mackerel, but also for large sharks and whales. I suspect that they are extremely important for hydroids, anemones and soft corals in the coastal areas. I have always read about how they are excellent food for aquarium fish. The main nutrient source is the lipids, or fat oils. The northern calanoids have a one year life cycle. It is based on growing almost to adult stage during summer. They reach the second last molting stage at that time. They build up a large store of fat in a container inside the body. At the end of the growing season they are like living oil tankers. In one species, Calanus glacialis, the oil can be 70% of the total body mass. So these creatures are real energy bombs. Then they go into a resting stage in the cold season, swimming down to deeper waters. This is why they need the large energy store. In spring they molt into the adult stage and swim up and spawn. During summer they spawn repeatedly. This one year cycle should make it impossible to keep several generations in a refugium. But I have understood that if the conditions are right they may skip the whole diapause and go direcly into adulthood and spawn. The whole development from egg to spawning adult can take as little as 30 days if the water temperature is 12C and the feeding conditions are perfect. So it is certainly worth a try. I can't wait to get my hands on those chillers.
Taken through a stereo microscope.
It was amazing to observe the bristle like feet moving. Fascinating animals!