How an ecosystem works
26 September 2007Add to My Folder
Help illustrate life processes by creating your own ecosystem, using brine shrimps
Brine shrimps are aquatic invertebrates found in tropical and sub-tropical areas. They live in salt lakes, which often dry out during the hottest months. Brine shrimps are ideal animals to illustrate life processes, since they are easy to establish and maintain and are very resilient. Don’t worry about who takes them home at the weekend, half-term break or summer holidays – brine shrimps will look after themselves! An aquarium tank of shrimps shows children how an ecosystem works, how a food chain operates, what plants are needed for growth, the role of micro-organisms and how brine shrimps move, grow and reproduce.
A great way to introduce the animals is with an overhead projector. Put saltwater into a glass dish and the children can see how adult shrimps (about 1cm long) move using their 11 pairs of legs, their swimming posture and how males and females get together to reproduce. The overhead projector can also be used for class investigations of their behaviour. For example, why do shrimps do backstroke in the aquarium, but front crawl on the overhead projector?
By observing shrimps, children can see how their tank ecosystem compares with a pond. Pond dipping allows them to compare water fleas (Daphnia) with shrimps. Water fleas have predators and predators are absent in a school aquarium. Adding fish (predators) to a tank would introduce moral/ethical dilemmas. A child could mimic a `flamingo` predator – a human hand holding a sieve that visits the tank every Friday afternoon, for example.
- Brine shrimps can be reared in a plastic bottle, so that each child can have their own ecosystem. Brine shrimps do best in a tank, but survive in a bottle for several weeks.
- Shrimps live in saltwater. Make this using salt (30-35 g/l) and tap water (leave the water in a bucket overnight to dechlorinate).
- Shrimps eat algae so establish plant growth in the tank before sprinkling brine shrimp eggs on the water.
- Shrimps are always moving! They swim on their backs in a tank, except when they flip over to eat algae growing on the gravel on the tank bottom.
- They have 11 pairs of legs which move them around and bring algal particles in the water to their mouth – their gills are also on their legs.
- The tank ecosystem has plants (algae), consumers (brine shrimps) and decomposers (micro-organisms) which cause the decay of dead algae and shrimps. For advice, see Activity sheet 7, ‘Establishing a tank of brine shrimps’.
- In summer, the water warms up so algae growth is faster, the water gets greener and the number of shrimps increases.
- Shrimps sometimes swim in pairs. A male grabs a female and they swim around together for several hours (courtship) before mating.
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