June 7 2011
May was, like April, a very intense month for the project. This may have been the month that really made clear the capabilities of my phytoplankton refugium. There have been many positive things, but also a major disappointment. I'll take that first to get it out of the way: After 7 weeks I have not managed to get the concentrations of algae cells very high. My blooms have typically given around 0.013 grams wet weight of algae per liter per day. Which is 1 gram per day in total food. A high quality continuous photo bio reactor can give up to 2.4 grams of wet weight per liter per day, 185 times more. Even my modest goal of around 0.07 grams per day on average was far from reached. This is bad news for the phytofuge as a food source.
On the positive side, at bloom concentrations the display tank gets hazy from all the biomass. That should indicate that the animals have good access to food. Perhaps they don't need more than a gram in total per day. Perhaps the actual biomass is higher than what I can measure. So there is still some hope that the method could work. Anyway, I intend to continue the project for a long while. There are lots of tests that need to be done. Also, I am very curious to just see what will happen to the little collection of animals that I have gathered. A positive thing about low production and continuous lighting is that CO2 addition is constant and pretty much optional. Most likely the production can work with just air bubbling. CO2 is by far the greatest cost of the setup. For me it is not an issue since I have a CO2 system. But perhaps it can be of use to other people. I really love the low maintenance level of this setup. It is so different from my algae aquarium. There are no daily maintenance rountines. With the algae tank there was feeding up to 5 times a day, daily cleaning of the overflow, and checking of the skimmer cup. Several times a week I had to clean the glass, prune and remove algae from pumps. This tank as no feeding at all. I do check the pH and adjust CO2 every day, but only because I want to. It is optional. There is weekly cleaning, plus dosing and measuring of nutrients.
Display tank, end of May.
Here is a summary of the 9 weeks that have passed since startup:
Startup week. Flow was 35 liters/day, allowing theoretical doubling time of 1.48 days. Visble growth from the start.
A heavy diatom bloom of, most likely Skeletonema costatum. It grew to concentrations of 420 million cells/liter. Water was colored red-brown. Based on size estimates this would give food output of 2 grams/d. There were also noticable concentrations of large flagellates and various other types of cells. Complete crash over night at the end of the week. Everything sank to the bottom and the water got clear practically over night.
This week saw low concentrations of algae. I introduced sand and the first animals.
Another bloom of smaller, non colonial algae, probably a type of diatoms was forming. Cylindrical cells of 5 micrometers in diameter and 3 micrometers height. At the max in week 5 the food value was estimated to cell concentrations of 430 million cells/l. There were fewer algae of other species. Noticeably lesser species diversity. The diatoms crashed at the end of week 5, but already before the crash concentrations of small flagellates could be seen. They were about 1.5 micrometers in diameter and had little food value because of the small total mass.
The pill shaped diatoms that bloomed in week 4 and 5. The smallest steps on the small scale are 1 micrometer. The steps on the large scale are 10 micrometer.
This is what a whole bunch of them looks like. (Roughly 37 000 000 000 of them in the refugium here).
The small flagellates bloomed with concentrations reaching 1200 million/l at max. But it was still far too little to give any significant food value. There seemed to be large concentrations of bacteria. I could even see clusters of large bacteria in the microscope. At the same time a third species of diatoms appeared. They had a characteristic shape with spines at the ends. This could be Rhizosolenia. The size was roughly 30 micrometers in length and 3 in diameter at the widest. At the end of the week the flagellates were disappearing fast.
A small flagellate of the type that bloomed can be seen next to the scale in the lower part of the picture. These flagellates have since become the most common algae in the refugium. They bloom regularly. The two spiny diatom specimens are probably Rhizosolenia and was seen for the first time this week. They have since been present all the time. The red arrows show what I presume to be bacteria. Next to the upper scale is a large flagellate that I have never seen in high concentrations, but is always present. They swim at high speed across my microscope field off view.
At the start of this week I changed the light regime from 18 hours of light to 24 hours of light. This gave better growth. But it did not stop the bloom cycles. I also did a large water change and inoculated the refugium with about 33% new seawater. There was a bloom at the end of the week. I increased flow to 60 l/d. This did not seemingly reduce the bloom. The bloom consisted of some medium sized, round, green flagellates that I had never seen before.
Green medium sized flagellates. Some unknown organism next to the one in the lower left corner. In the upper right corner there may be cell splitting going on. I often observed them in such clumps of 3.
The above mentioned flagellates blooming.
At the start of the week the bloom was waning. I decided that since the refugium was very dirty, and it was more than 7 weeks since startup it was time for a cleaning and restart of the refugium. Small blooms of diatoms and flagellates occured during the weeks. Never any high concentrations of biomass like in the start. If found that strange.
Emptying the refugium for a dry out and complete restart.
When emptying the refugium I saw thick swarms of harpactoid copepods gathering at the bottom. They had multiplied to great numbers during the 7 weeks. I consider that very positive as they are also valuable food, though it is hard to measure their food contribution.
Planktic copepods, probably cyclopoids, are always present in the refugium.
My two species of sand burrowing clams, Cockles (Cerastoderma edule), and another species that I haven't identified, seem to be doing very poorly and dying. The deaths started only 2 weeks after I introduced them to the display tank. I don't know why this is happening. None of the other animals are showing similar signs.
I had many nice collection trips in April and May. Here are some pictures.
This oyster was big, but I was lucky to find a beautiful small specimen for my display tank too.
Brittle stars in current exposed location.
One of the largest chitons I've seen.
This dahlia anemone (Urticina eques) was roughly 25 cm in diameter.
I was very lucky to find a specimen of Sea cucumber (Cucumaria frondosa), which is the black large creature in the middle of the picture.
Dead man's fingers (Alcyonium digitatum).
The black brittle stars (Ophiocomina nigra), are both filter feeders and scavengers. So the dead clams didn't go to waste.
I found two large sponge colonies. I am not sure of the species yet.
Sea squirts (Ascidia virginea), and Sea vase (Ciona intestinalis).
I haven't been able to identify this species.
Sea squirt (Ascidia virginea), and Sea vase (Ciona intestinalis).
Pink sea squirt (Ascidia mentula).
Unidentified, maybe Pink sea squirt (Ascidia mentula).
One thing that is really frustrating for an aquarist is to be stuck. Basically to know that there is a problem, but simply not be able to find its cause. My cell concentration problem is like that. There are a number of possible causes to why cell concetrations of all types of cells grow to a certain point, and stop. For example high concentrations of bacteria that attack phytoplankton. Virus or some type of microscopic grazers are also a possibility. Or, most likely, something that I just don't have a clue about what is. Right now I am testing out the simplest hypthesis, namely that it is caused by nutrient limitation. I didn't think that could be the cause earlier because the two nutrients that I can measure; nitrate and phosphate, are present in sufficient concentrations during crashes. And the F/2 medium should be fairly balanced. I have also tried dosing more nutrients when I see reduction in cell concentrations, without seeing any changes. But I still think there is a possibility for nutrient limitation. My current dosing scheme should make it clear.