Final answer:
Estuaries are considered embayments because they are semi-enclosed coastal bodies of water where fresh and salt water mix, resulting in brackish water with significant salinity fluctuations.
Step-by-step explanation:
Estuaries are considered embayments because they are semi-enclosed coastal bodies of water. These biomes occur where a source of fresh water, such as a river, meets the ocean, resulting in the mixing of fresh water and salt water. This mix creates brackish water and makes estuaries essential protected areas for the early life stages of various marine organisms. The salinity in estuaries is dynamic, varying considerably based on factors such as the flow rate of freshwater sources and the occurrence of high and low tides, which contribute to significant fluctuations in the water's salinity and therefore the conditions of the habitat.
Animals and plants in estuaries are adapted to cope with these variations. For instance, many estuarine plants are halophytes, capable of tolerating saline conditions, while animals, like mussels and clams, exhibit behavioral adaptations to the rapid changes in their environment, such as closing their shells and switching respiration methods in response to different salinity levels.