The organisms selected (sea squirts, mussels, fiddler crabs, soldier crabs and mud-skippers) are in fact nutritionally interdependent of each other. Some of them are being fed, and some of them are fed on others. They are said to be in different trophic levels, classified as the producers, primary consumers, secondary consumers, and tertiary consumers. Producers are those autotrophs, while consumers are heterotrophs.

Sea squirts and mussels are fed on phytoplanktons (a photosynthetic organism). As phytoplanktons are producers, therefore sea squirts and mussels are known as primary consumers. Since they feed on the same organism, so their relationship is known as competition.

Fiddler crabs and soldier crabs are fed on sea squirts and mussels (which are primary consumers), they are therefore known as secondary consumers. As they are the predators, sea squirts and mussels are the preys. This relationship is called predation. Moreover, there is competition between fiddler crabs and soldier crabs since they are fed on the similar preys.