Daphnia culture

I noticed my Daphnia magna cultures are beginning to proliferate, the days are getting longer and unicellular algae is starting to replace the strings of hair algae. I've noticed as the Daphnia magna start hatching out of resting eggs the daphnia are quite large, some as much as 6mm or more across. My 6500 gallon vat has the biggest daphnia, i was wondering if anyone else has noticed their daphnia cultures coming back and if the Daphnia are bigger than they are when the weather is warm? All these daphnia are females giving live birth, the males are absent and will not appear until September or October. I am thinking that the evolution of the population of large daphnia at the beginning of the season gives way due to environmental influences or do different species of daphnia replace the big ones as the season progresses. Summer daphnia are maybe half the size, at best, of winter daphnia, also behavior changes as the seasons progress as well with late summer daphnia clinging to the sides of vats instead of swimming freely. Any thoughts?

Oh yeah, the bigger daphnia seem to grow when the cyclops are dormant and give way to smaller daphnia as the cyclops become active...

Ah, ha ha ha, ha ha ha. You're in North Carolina. I'm in Cleveland. As you notice your daphnia cultures come back, I notice the foot of snow on the ground. My local weather estimates 4.7 inches have fallen in the last 24 hours.

Here's a paper that might interest you: http://www.sekj.org/...z30-299-311.pdf

Edited by EricaWieser, 01 February 2011 - 11:14 PM.

I'll bet those trophy-size Daphnia didn't hatch out recently, but have been laying low down in the mulm since fall. With less competition they can grow more, and it's been too cold to spend energy making babies, so all their energy goes toward growth.

I had doubts about this overwintering effect on daphnia size, but this supports it:

http://en.wikipedia....aphnia#Lifespan

The lifespan of a Daphnia does not exceed one year and is largely temperature dependent. For example, individual organisms can live up to 108 days at 3 °C (37 °F) while some organisms live for only 29 days at 28 °C (82 °F). A clear exception to this trend is during the winter time in which harsh conditions limit the population in which females have been recorded to live for over six months. These females generally grow at slower rate but in the end are larger than ones under normal conditions.

The effect of cyclops may still play a role.

Abstract: http://plankt.oxford.../4/739.abstract

Experiments were conducted in a mesotrophic North German lake to examine the influence of metazoan zooplankton on the microbial food web. The presence and absence of Daphnia and Cyclops were manipulated in two cross-classified in situ experiments conducted in May and June 1994, during and after the clear-water phase. Ciliates had high population growth rates in the absence of predation during the clear-water phase, but had much lower growth rates 1 month later. Cyclops had strong predation effects on both Daphnia and ciliates. During the clear-water phase, manipulating metazooplankton abundance resulted in shifting the algal grazer community to either primarily metazoans or ciliates, but did not alter the final chlorophyll a concentration. After the clear-water phase, Cyclops had a negative effect on picoautotroph abundance, possibly due to reduced nutrient recycling resulting from the suppression of ciliates by Cyclops. Daphnia had both direct predation and indirect enhancement effects on bacteria, dependent on Daphnia biomass. These experiments indicate that while multiple strong links exist between the classic and microbial food webs, the net effect is not necessarily a clear trophic cascade from metazoan zooplankton to bacteria.

I have a very small tank which has been established since last winter when I stocked it with scuds and daphnia intended to supplement frozen food for my fish. The scuds never took off in the small space and cyclops soon became the primary critter. In the spring I grew out some spotted salamander larvae in there. During that time I promiscuously dumped in all kinds of mulm, plants, inverts, insects and whatever caught my fancy. Did great for growing out the salamander larvae to a size to take frozen. Once they were removed, the tank sat in a shaded window mostly ignored. I topped off water and tossed in an algae wafer once and awhile for the heck of it but never changed water or did any other care. There is no filter. The substrate is pure mulm, mostly snail crap as the pond snails did well in there.
Recently I obtained some twolined salamander larvae from a spring seep buried under 2 feet of snow and decided to grow them out in the tank. On close examination I found the mulm was crawling with scud and cyclops were not plentiful but present in decent number. No daphnia had been seen for a very long time - until I moved the tank to a sunny window. Now I can see small daphnia are starting to get ahead of the cyclops. My theory was the sunny window triggered some dormant daphnia eggs.
Not surprisingly, the sallie larvae like their new home.