What organisms would starve if phytoplankton became extinct?

If phytoplankton became extinct, a wide range of marine organisms would face starvation, particularly those that rely directly on phytoplankton as their primary food source, such as zooplankton. This, in turn, would impact larger marine animals, including small fish, which depend on zooplankton, and ultimately larger predators like whales, seals, and seabirds. The loss of phytoplankton would disrupt the entire marine food web, leading to significant declines in biodiversity and ecosystem health.