User:Collin Hendricks/sandbox

Food Chain
A food chain is a system of links that makes up a food web and represents the order in which organisms are consumed from one trophic level to the next, and each link in a food chain correlates to one trophic level in the ecosystem. The numbered steps it takes for the initial source of energy stating from the bottom to reach the top of the food web is what is known as food chain length (citation 22). While food chain length can fluctuate, aquatic ecosystems start with primary producers that are consumed by primary consumers which are consumed by secondary consumers, and those in turn are consumed by tertiary consumers so on and so forth until the top of the food chain has been reached.

Primary Producers
Primary producers start every food chain. Their production of energy and nutrients comes from the sun through photosynthesis. Algae contributes to a lot of the energy and nutrients at the base of the food chain along with terrestrial litter-fall that enters the stream or river (citation 2). Production of organic compounds like carbon are what get transfered up the food chain. Primary producers are consumed by herbivorous invertebrates that act as the primary consumers. Productivity of these producers and the function of the ecosystem as a whole are influenced by the organism above it in the food chain (ref 23).

Primary Consumers
Primary consumers are the invertebrates and macro-invertebrates and are the organisms that consume the plant and algal primary producers. They play an important role in initiating the transfer of energy from the base trophic level to the next. They are known as regulatory organisms as they are depended on and control rates of nutrient cycling, mixing of aquatic and terrestrial plant materials, and are relied upon for transportation as well as nutrient retention of some of those nutrients and materials (citation 1). There are many different functional groups of these invertebrate that include grazers, organism that feed on algal biofilm that collects on submerged objects, shredders are those that feed on large leaves and detritus and helps breakdown large material, filter feeders are macro-invertebrates that rely on stream flow to deliver them fine particulate organic matter (FPOM) suspended in the water column, and gatherers who also feed on FPOM that is found on the substrate of the river or stream (citation 1).

Secondary Consumers
The secondary consumers in a river ecosystem are the predators of the primary consumers, this includes mainly insectivorous fish. Consumption of the invertebrate insects and macro-invertebrates is the net step of energy flow up the food chain. These predatory consumers can effect all trophic levels below it and can shape an ecosystem depending on the abundance of these secondary consumers. When fish are at high abundance and eat lots of invertebrates, then algal biomass and primary production in the stream is greater, and when secondary consumers are not present, then algal biomass may decrease due to the high abundance of primary consumers (ref 17). Energy and nutrients that is started with primary producers continues to make its way up the food chain and depending on the ecosystem, may end with these predatory fish.