Organisms interact with one another in very complex ways in order to gain energy necessary for life. Depictions of food chains often show theses relationships as simple pictures, depicting one organism eating something and it in turn being eaten by something else. Instead of thinking of these relationships as a chain they are better represented by a web. A food web is able to encompass all of the food chains in a given habitat or environment.
Every food chain, no matter how big or how small, begins with producers, because they are the only organisms that are able to make their own food, through a process called photosynthesis. Plants are the most well known producers, but some bacteria can do this too, especially cyanobacteria which photosynthesize and are responsible for perhaps most of the world's photosynthesis. Photosynthesis involves taking in energy from the sun and transforming it into food. Plants are thus referred to as primary produces. Although they are at the bottom of the food chain they are actually located near the top of the Long Island Sound water column, because they need proximity to sunlight to do their very important job. Most plants in the Sound are a special type of one-celled (unicellular) organism called phytoplankton. Multicellular plants, such as macroalgae and seaweeds, are usually found in shallow waters along the coast.
Animals are all consumers because they are not capable of producing their own energy. First-order consumers, or herbivores, feed on plants. Zooplankton (tiny animals that float in the water column), several fish (herrings and sardines), shellfish, and some crustaceans (crabs and shrimp) are found in this group. The next group, second-order consumers, or carnivores, are animals that eat first-order consumers. This group is made up of fish and birds. Third-order consumers eat second-order consumers and include mammals, such as seals and otters.
While producers make the energy necessary for the food chain to flourish there are also special organisms that break down once living things. These organisms, known as scavengers and decomposers, play a special role in the ecosystem by breaking down dead plants and animals into nutrients. Once broken down these nutrients are released into the water and settle on the ocean floor, where other organisms can use them. Without decomposers energy would not circulate through the ecosystem, which would lead to breaks in food chains and trouble for the Sound ecosystem. It is also important to note that there are varying amounts of mater at each level of the food chain. A food pyramid is a great way to visualize the number of organisms at each level. Primary producers would make up the pyramid's base and then first-order, second-order, third-order and so on, as you climb the pyramid.