Re: What is a detritus based food chain? aren't all food chains detritus based?

Food chains and food webs are ways of representing the trophic relationships (i.e., what eats what) in an ecosystem. The concept was originated by Charles Elton and Victor Summerhayes in 1923, who examined the network of relationships on a Norwegian island. A food web represents all the relationships in an ecosystem, while a food chain describes one branch in the web; for example, plants--> caterpillars--> sparrow --> eagle. You can find a more detailed description of food chains and food webs here.

The base of a food web is the fundamental resource on which all the other relationships ultimately depend. In most terrestrial ecosystems (that is, on dry land), plants form the base of the food web: if plants were eradicated, very little else would survive.

In aquatic ecosystems (under the water), food webs can have a different base. Some areas, like fast-flowing streams, are too harsh for plant growth, and in other areas, such as the deep waters of lakes or oceans, there is not enough light for plant growth. The food webs in these areas depend on detritus—the organic matter (dead leaves, dead animals, etc.) that filters down from the ecosystem above.

Detritus plays an important part in all food webs, both terrestrial and aquatic. A group of organisms known as decomposers (mainly fungi and bacteria) break down dead matter and return the nutrients to the ecosystem. However, only a small set of food webs-- those that depend entirely on the input of organic matter from other ecosystems-- can really be described as detritus-based.

Literature cited:
Summerhayes, V.S., and C.S. Elton. 1923. Contributions to the ecology of Spitsbergen and Bear Island. Journal of Ecology 11:214-286.