March 7, 2015

6 weeks

The system has been running for 6 weeks now. It is clear that the absolute best case scenario did not happen. That would be if the zooplankton aquarium was a dense swarming mass of copepods by now. But that wasn't all that realistic really. At the time of writing there isn't any clear evidence of a bloom of pelagic copepods. The benthic ones are blooming though. They are all over the walls in the zooplankton aquarium, scraping them pretty clean.

Phytoplankton tank

This has worked just fine. There are two differences I have noticed, compared to the previous plankton project: First, it is more stable, but with a bit lower concentrations at peak. Still there were some mild crashes. Second, the benthic copepod bloom hasn't come even after 6 weeks. It looks like it is on its way now, but the walls arent exactly scraped clean yet. This may be due to the lower temperature of 16.5 degrees versus 22 or more in the first plankton project where I didn't have a chiller. So perhaps the bloom happens soon.

Phytoplankton aquarium

Nice early bloom in the phytoplankton aquarium.

Phytoplankton aquarium
Phytoplankton aquarium
Phytoplankton from aquarium

Some phytoplankton photographed through the lens of the microscope with 400x magnification.

Zooplankton tank

This was seeded with copepods from 3 different catches. The first one was with 25 micrometer hand net. Only one or two adult calanoid copepods, plus a small swarm of nauplii was in this. The second, and by far the largest, was with both a 25 micrometer net and my large hand net which is probably 250 micrometer. It was a my favourite plankton spot, and the wind was favourable so the place was swarming with zooplankton. There was a great variety in this catch; many large and small calanoids, cyclopoids and nauplii. Even a few amphipods and sea star larvae. When I say large calanoids I mean 2 mm body length. During the first 48 hours there was a great die off of those. Only a few dozen are still alive. In general, when looking into the tank with a flashlight, I haven't seen any signs of a bloom in the water column in these 6 first weeks. In fact, I have gotten the impression there has just been a slow die off all along. On the walls and bottom though there is clearly a bloom of cyclopoids, and probably harpacticoids. They are keeping things clean and neat.

zooplankton aquarium

This is the cone from my flashlight in the zooplankton aquarium just after having seeded it. You can see large and small calanoid copepods.

zooplankton aquarium

Most of the calanoids died within 48 hours, as usual.


I have noticed that some small calanoid copepods, with body lengths less than a millimeter, carry egg clusters. Since only adult females do that I know that these are a different species from the large ones. When studying water samples closer I found at least 25 nauplii and copepodites per liter of water. This is a good indication that there is some serious reproduction going on. So I am crossing my fingers for the coming weeks!

Calanoid copepod females with eggs

The main body part (prosome) of these female calanoid copepods is about 1 mm long. It is impossible for me to know the species or genus since there are many candidates, and I don't even have a list of possibilities. But they carry eggs, which is a great sign.

Calanoid copepod female

This is a female the same size as the ones above. She lost the egg sack and got squished during handling. The thing below her came out of her stomach I think. A parasite, fecal pellet or the stomach belly. Perhaps with dinoflagellates inside.

Calanoid copepod

One of the large calanoids. 2-3 mm long. There are still a few of these alive now, after 6 weeks.

Calanoid copepod

A very smal individual, perhaps 0.5 mm prosome length. Maybe a juvenile.

Copepod nauplii

Copepod nauplii.

Other copepods

There are also both cyclopoid and harpacticoid copepods in the water column.

Cyclopoid copepod

Cyclopoid copepod. 0.5 - 1 mm (both body parts included in this length), but not rear antennae.

Harpacticoid copepod

Harpacticoid copepod from the water column.


My homemade chillers have been working fine so far. A little algae growth on the heat exchangers, as expected, but that is easy to brush off. No visble rust so far.

Plans ahead

The plan ahead now is just to wait and see how things develop. Will the phytoplankton tank keep working? Will there be large numbers of calanoids, or anything? I am planning to just let things run for awhile without changing anything. It is always tempting to try to correct things when one is waiting for things to happen and feeling that it is not going in the right direction. But this is an experiment, ideally the situation must be stable and only one parameter changed at a time for tests to be reasonably valid.

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