Algae
Algae are simple unicellular or multicellular organisms and most species are autotrophic. (Autotrophic organisms use light energy or energy from chemical reactions to produce complex organic compounds from simple inorganic molecules.) Algae are believed to be the ancestors of our modern day higher plants and both groups still have a lot of things in common. In addition to photosynthesis, some species of algae derive energy by absorbing organic compounds through osmosis, by sucking out the cellular content of cells with a special feeding tube, or by engulfing particles with their cell membranes. Algae are of imperative importance in the ecosystems where they exist, but they can turn into a problem in man-made structures, such as pools, ponds, showers and aquariums. In ponds and aquaria, excessive algae growth can cause water quality problems and fish can also become entangled in long strains of algae. The solution is usually to add algae eating animals, such as certain types of fish and snails. Limiting the light, e.g. by placing aquariums in a spot where they do not receive natural sunlight, is also a good idea if you have problem with excessive algae growth. Ponds are more difficult to move, but limiting the amount of available nutrients can work well, e.g. by making sure no garden fertilizers reach the pond.
