Marine life appeared in the form of fish, which live exclusively in water. Some of these evolved into amphibians which spend portions of their lives in water and portions on land. Other fish evolved into land mammals and subsequently returned to the ocean as seals, dolphins or whales. Plant forms such as kelp and algae grow in the water and are the basis for some underwater ecosystems. Plankton, and particularly phytoplankton, are key primary producers forming the general foundation of the ocean food chain. Marine invertebrates exhibit a wide range of modifications to survive in poorly oxygenated waters including breathing tubes (see
Anthropology of food of food anthropology" for his work "Sweetness and Power (1985)," which linked British demand for sugar with the creation of empire and exploitative industrial labor conditions. Research has traced the material and symbolic importance of food, as well as how they intersect. Examples of ongoing themes are food as a form of differentiation, commensality, and food's role in industrialization and globalizing labor and commodity chains. Several related and interdisciplinary academic programs exist in the US and UK (listed under Food studies institutions). Anthropology of food Anthropology of food is a sub-discipline of anthropology that connects an ethnographic and historical perspective