Final answer:
Estuaries are biomes where fresh water meets the ocean. They exhibit fluctuations in temperature, and seasonal temperature changes can affect phytoplankton populations in some estuaries.
Step-by-step explanation:
Estuaries are biomes where a source of fresh water, such as a river, meets the ocean. They exhibit fluctuations in temperature, and in some, seasonal temperature change promotes changes in phytoplankton populations as a function of intensity and duration of sunlight exposure. Phytoplankton are microscopic plants that float in the water and are the primary producers in the estuarine food chain.