Detritus (da-tri-tus) is defined as the loose fragments of grain worn away from rock. The word is more commonly used to describe tiny pieces of organic material that have decayed and dissolved into the water. For us, it means the tiny left overs from dead plants and animals, that weren't eaten by other animals and have found their way into the water system of the marsh. This organic material is still rich in nutrients, but requires special organisms which can make use of their life-giving components.
Marsh grass is one of the most productive crops on the planet. Only sugar cane is more productive in terms of bio-engery produced per acre. While we don't harvest it as a crop, it fulfills a must greater role in nature, acting as an important crop for entire the chain of life. When marsh grass dies, a great deal of organic-fixation occurs in the muck beneath it. (Over a huge period of time, these marsh lands will become great petroleum reserves.) But, much of the organics are released in the form of detritus.
Through out nature (and life, in general), we find different niches. A niche is a special opportunity that is afforded someone or something because of a special ability. In the marsh, the abundant mixture of salt water and detritus that is caused by the massive pumping action of the tides affords a special niche to organisms which can thrive in that mix. That stellar performer is an underappreciated little form of life, called phytoplankton. The story of what they do is this environment, is the story of the beginnings of the food web, itself. Now that you know how nature's soup is created by the tides, the salt water, and the decay from the marsh, read on to find phytoplankton process natures soup into the cornerstone of life.