Coldwater marine aquarium Blog 2009 March
March 31 2009
Ulva sp.

A very nice bloom of Ulva sp. is coming along.

It's spring and the light has returned in full. It is very visible in the tank, the growth is enormous. The nitrate concentrations went from 50 mg/l to 5 mg/l in a few weeks. The daylength just passed 12 hours and this probably the best time for algal growth. It is the time when the ocean water is at its coldest. With the heavy light input my chiller is just able to keep the tank temp at 7C, which is warmer than the ocean, but I can live with that. Like last spring, there is now a bloom of Ulva sp. sea lettuce. There are hundreds of small leafs, most of which are a few millimeters in diameter. But the largest ones are now about 4 cm.


I hope that my wrack (Fucus sp.) are going to do better with the new added flow. This speciemen is placed in the middle of the jet stream from my new pumps, and it clearly is suffering from less epiphytes than those with less flow. It has shown some growth this spring. I like the ability these algae have to create a forest with a floating canopy. I see many nice epiphytes growing on them too.

Fucus sp.

A new shoot of Fucus sp. Perhaps second generation. It does not have the strongest flow and is starting to get some thread algae epiphytes coating it.

Fucus sp.

This is a new specimen of Fucus sp. It has a lighter color and much less epiphytic growth.

Collection trips

It is nice outside now with the light returning. The tides are low at this time of the year.

Xantho pilipes

Xantho pilipes

Xantho pilipes

Xantho pilipes in natural habitat. Just after I removed the rock above it.


Phyto equipment

Phyto equipment, except light.

One of the things I've been trying out the last month is growing phytoplankton. I have been thinking about a future non photosyntetic system with a large phytoplankton refugium. The idea is to feed and filter the system by growing phytoplankton. It would then be a complete ecosystem. The traditional way to grow phytoplankton in the aquarium hobby and other industries is to use reactors with algal monocultures. Common lore stresses the importance of avoiding contamination of the cultures, or they will crash. If an ecosystem aquarium is to succeed, it must be possible to grow phyto without a monoculture and with zooplankton contamination. So I set up this test system. It is an ordinary setup with an 11 Watts compact daylight bulb, an air pump, and a few millilitres of flower fertilizer. I used 2 1.5 liter bottles. Then I added ordinary seawater to the bottles, no algal culture. There were even some visible zooplankton speciemens in the bottles, but they died after a few days.

Phyto growing

After 2 weeks.

According to my understanding it would be at least 100000 phytoplankton cells in each bottle. Probably much more. It should take only 14 days before there would be a concentrated culture. I must admit I didn't have all the faith in the world in this project. After a week the water was still crystal clear. I grew impatient and added a about 50 ml concentrated plankton that I had collected with my 25 micron plankton net, to the second bottle. This was mainly brown diatoms. But lo and behold, after 2 weeks, the first bottle was getting green. The second, with concentrated diatoms, was getting brown. Picture is taken after 2 weeks. Now after 3 weeks, the cultures are fairly concentrated. But growth is definitely not exponential anymore. I must test various parameters and see if I can find the growth limiting factors. The factors can be: Light, CO2, nutrients, zooplankton predation, temperature, bacteria or fungi.

Plankton time again

Calanus Finmarchicus

Calanus Finmarchicus. Unlucky stickleback got caught in the net too.

It is the spawning time of the Calanus Finmarchicus copepods again. I got 300 grams of them the other night. A Norwegian company is currently researching the possibilities of using these as food for aquarium fish. One of the challenges was to keep them in the freezer in good condition. The enzymes keep working even in the freezer. So important fatty acids are broken down and lost. That was useful information for me since then I know why this, and other frozen fish food, has very limited storage life.

Flatworms and copepods



The bright orange flatworms that were with me last year are back now. I see them on the same type of algae in nature. I assume they have some sort of chemical defence to protect themselves from my wrasses. In the spots that are not too exposed to flow they are crawling all over the algae. I think they make slime nets to trap small particles in, but I am not quite sure. I was wondering if it was an infestation of my tank, but I see them in just as large concentrations at certain spots in nature. So they belong here. But the reason I wondered, as you can see, is that the algae in these spots are covered with fairly much decaying biomass and mucus like substance. Not very nice looking, but then again, this is nature not a flower garden.



Flatworm and copepod

Flatworm and copepod. The flatworm is about 3 mm length.




Female copepod with eggs

Black spot disease

Black spot disease

Black spot disease

I've had my three rock eels (Pholis gunnellus) for more than a year now. They have always had some black spots on them, and I've always feared that they may be parasites. I felt the parasites had become multiplied or worse somehow, because it was like I could see the fish suffering. There was something about the skin. When searching on the net I found that it is probably a common flat worm disease (Cryptocotyle lingua). So I decided to take these fish out. I have gotten two of them now. Third one is still evading me.

Black spot disease

Black spot disease

Worm spawning

Cirratulidae worms

Cirratulidae worms mating

This year I've had at least 3 species of larger polychaete worms laying eggs in the tank. In addition to the small round egg balls from last year I have these Cirratulidae worms mating openly.



Painted gobies

Painted Gobies. Males posing.

Painted gobies

Female. Waiting to see who's the winner.

Red algae

Second generation specimen of this nice red algae.

Neanthes virens

Neanthes virens, about 12 cm.


The largest specimen of kelp I have removed. The table is 90cm diameter.


Doris pseudoargus, I think. Eats the sponges under the rocks.

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