Final answer:
The Southern Ocean food web starts with phytoplankton consumed by krill, which in turn form the diet of a variety of predators including fish, seals, and whales, within the productive Subtropical Convergence zone.
Step-by-step explanation:
The Southern Ocean food web is a complex system of energy transfer between organisms living in the cold southern waters where the cold, dense waters of the Southern Ocean meet the warmer waters of the Pacific, Atlantic, and Indian Oceans. This zone is known as the Subtropical Convergence, characterized by upwelling and mixing, which promotes high productivity levels for phytoplankton and krill, the latter being a crucial link in the food chain.
At the base of the web, phytoplankton convert solar energy into biomass, which is consumed by zooplankton. This relationship is central to the food web, as zooplankton, in turn, are prey for various larger marine animals such as fish, penguins, seals, and whales. The food web also includes birds like the albatross that feed on fish, krill, and other marine organisms. A fisheries practice called 'fishing down marine food webs' shows a top-down impact on this system, where larger fish are targeted first and, as they deplete, smaller species lower in the food web are fished, potentially disrupting the ecosystem balance.