Chapter 3 Overview of Aquatic Ecosystems Trophic level Structure Organisms interrelate through their feeding mode Each organism has a feeding or trophic level defined by where it is located on the food chain Organisms on one level feed on organisms on the level below (figure 3.4) Healthy Ecosystem Food chains within interrelate and interconnect to form a food web (figure 3.2) The more complex the food web, the stronger and healthier the ecosystem   Greater diversity of species High diversity can mean less stress from pollutants and other destabilizing forces Simplicity breeds instability in an environment Contaminant Transfer Contaminants can be soluble in fats and oils but not water. These can be absorbed across membranes and stored in body fat reserves Contaminants can be absorbed as into a shell Contaminants can be acquired through ingestion  Contaminants can be excreted to some degree  Many synthetic chemicals cannot be broken down and are retained. They can bio-accumulate in a body (figure 3.8) Bio-magnification Takes place as organisms in each trophic level feed on the level below and increase levels of concentration as they go (figure 3.9) Environmental Fate The end result of the source-pathway-sink concept of pollution Impact of pollution on an environment can be studied through the distribution and population of benthic macro invertebrates

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