Zooplankton are small, drifting animals that live in the ocean. They are an important part of the marine food chain, as they are a primary food source for many larger animals, including fish, whales, and sea birds. Zooplankton come in a variety of shapes and sizes, from tiny single-celled organisms to larger, more complex creatures like jellyfish and krill. They are found throughout the world's oceans, from the surface waters to the deep sea, and play a crucial role in maintaining the health and balance of marine ecosystems. Zooplankton populations can be affected by changes in ocean temperature, acidity, and nutrient levels, making them an important indicator of the health of the ocean as a whole.