April 26, 2015
It is now 3 months since startup. No success with growing large concentrations of plaktonic copepods so far. But I have learned a lot of interesting things though, and gained some knownledge of what seems to work and what doesn't. The short story is that calanoid copepods die off at a steady rate from the time I introduce them. I know that some survive for up to 8 weeks. But those are only a few of the hundreds I introduce in every seeding. The main problem isn't really the die off, but that there doesn't seem to be successful reproduction among them. I see very little nauplii, even though there are females with eggs. So it doesn't look that great for producing copepods right now.
One of the really interesting things that have happened the last month is a bloom of medusae, jellyfish. Incredibly enough these delicate creatures have managed to reproduce in significant numbers in the tank. I assume they are automedusae that are entirely planktonic, without any benthic polyp stage, but there could be polyps somewhere in the system. I see hydroids growing in various places. The size is about 2 millimeters across the bell, max. I haven't done any biomass measurements here, but I guess 20 to 50 of them per litre. The average size may be about 1.5 millimeters which could add up to some significant biomass of gelatinous plankton. This could be a path worth investigating more. The fact that these are thriving indicates that too strong water flow and turbulence isn't a problem in the system. And the successful reproduction of yet another type of animal indicates that the chemical environment isn't the problem either. They could be a problem for copepods, because they have tentacles that are close to 10 millimeters long. The tentacles spread straight out from center in a plane to form a large circular hunting net. I have observed copepods being caught in them.
These are about 1.5 millimeters across. Often they have tentacles of close to 10 millimeters length. The long tentacles are torn off these though.
What is it that prevents the copepods from reproducing? I am always worrying about poisoning from some fertilizer chemical, metabolites, or metal from the heat exchangers. But when so many organisms can reproduce, including benthic copepods, what is the probability of that? Lack of food should not be a problem. Neither should turbulent flow. One thing I can think of is predation on eggs and nauplii. Perhaps both benthic and planctonic animals eat them.
Since copepods are crustaceans I tended to look at them as rather physically tough, like shrimp, crabs, benthic amphipods etc. But I have have gotten some good indications that the planktonic ones, particularly the calanoids, are not. I was very optimistic about a new way of catching them which was basically trawling in a tidal current with a plankon net specifically made for this. It even has a small holding chamber in the bottom that should allow them to stay safe from being crushed into the fabric. The first time I held the net in the current for about 30 seconds at a time. The catch was small and had a lot of dead or dying copepods. The second time I hung the net in the current for about 5 minutes each time. This time the catch was OK, but there wasn't a single survivor among the adult copepods. So I gave up this strategy and tried my trusty old hand net. The next time I was very lucky and found absolutly ridiculous amounts of plankton at my favourite spot. I was careful to just dip the net into the water for a few seconds. The result was that there were hardly any losses at all among the thousands of copepods I caught. So I concluded that extremely careful handling is the key. The problem is that this makes it very hard for me to catch copepods in places with low concentrations. So it makes it difficult to get different species than the ones I have tried already.
A big catch of calanoid copepods.
This tank has worked better than expected. I have not restarted it the whole time. But it is still delivering the usual amount of phytoplankton. There have been 2-3 "crashes". But it has recovered. Usually crashes have been caused by nutrient issues. Sometimes the amount of benthic algae material has probably sucked up the nutrients. But that can be solved with a fine masked hand net. I just scoop/scrape it up with that and kick start with some extra nutrients. The variety of life forms is amazing. In addition to the usual algae there are large numbers of dinoflagellates and ciliates.
The phytoplankton aquarium during an early crash. The bowl on the bottom is from my benthic copepod seeding.
A sample of the "mud" on the bottom of the phytoplankton aquarium.
The same mud. Up close we can see that it is algae. In the middle there is a copepod. Pretty much every white spec you can see is a dinoflaggelate swimming at high speed.
An egg in the middle?
A bottom sample from the zooplankton aquarium. Dominated by what is probably copepod fecal pellets. A copepod, swarms of dinoflagellates, worm shaped ciliates, and round ciliates.
Another bottom sample from the zooplankton aquarium. Here you can clearly see the large number of dinoflagellates as white specs.
I will keep running the project for some time, trying to catch copepods in different places. I don't have any ideas for changes though, so unless some new and better fit species pops up there isn't a clear way to success here. I will look for places with large concentrations of smaller calanoids or cyclopoids. I plan to restart the zooplankton aquarium with a complete cleanout to start over without any medusae. But the copepods weren't successful before the medusae came either. So that may not change anything. I also plan to see if I can change the algae flora. I want to try something different than diatoms. Diatoms have chemical defences against copepods. So who knows, there may be something there. I have never really tried to not grow diatoms before. The plan is to stop dosing silicon and see what happens.