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RE: self-contained ecosystem
Rice writes:
> << She said that these shrimps live by eating
> > the algae that grows inside the sphere, and, in turn, the algae grows on the
> > waste. Light is provided by normal room florescent. She also says that the
> > shrimps live from 5-10 years and by the time they die, they will have
> > already had many baby shrimps to replace them. I figured that the shrimp
> > population in this sphere is checked by the amount of food they have,
> > which is dependent on> the amount of light. >>
Bob Dixon (IDMiamiBob <IDMiamiBob at aol_com>) responded:
> With any attempt you make at this, the balance in a sealed container system
> will find its own balance between the photosynthetic producer and the animal
> living off it. The trick is to figure out what species to use, and then
> introduce only those two species.
I believe Bob is right. This "self-contained system" concept has been a
hobby of mine for a number of years now. The spheres in discussion
are just as Rice describes, a sealed glass ball with algae, marine water,
marine algae, and a small pocket (20-40%) of air. They are the commercial
results of research conduced by NASA and other organizations over the
past few decades on sealed viable systems.
Of course, the interest by NASA is obvious: Determine factors for sealed
systems so one can remain viable N-days in orbit. The goal has been to
increase the number "N".
Olga Betts <sae at arts_ubc.ca> asked:
> Am I wrong in thinking that this would be impossible. Surely the sphere
> could not be completely enclosed. The living things would need air.
You are correct. These spheres must have some air, and they do,
ranging from 20-40% air. However, because the low oxygen demands by
the brine shrimp, and the oxygen production potential of the algae, the
sealed glass sphere is able to recycle the oxygen. This fails if the sphere
remains in the dark: If the algae "oxygen factory" does not get light
input, it effectively shuts down, oxygen becomes limited, and the brine
shrimp die. Presumably, anaerobic bacteria can then attack both the
algae and the dead brine shrimp and you have a failed system (no restart).
When these were first sold, they ranged from $40 to $120 (the larger ones
being the most expensive). Then, the novelty wore off and the price
dropped. Warranties for viability ranged from 6 months to a year, but
nobody warranties them after a year. I seem to recall such systems
living as long as 6 years with good light input and temperature
control (try to keep them from overheating). However, they all fail
after a period of time with no restart.
This only works at the very lowest trophic level. Since only 10%
of biomass actually gets converted into additional biomass at the
next level (90% is lost to energy expenditures), and since photosynthesis
is only about 2% efficient, it is prohibitive (today) to build any sealed
system with any three trophic levels that lasts more than a couple
years. Any animal with real oxygen demands makes this much more
difficult.
--charley
charleyb at cytomation_com