Final answer:
A true statement about estuaries is that they represent a close interaction between land and sea. Estuaries are highly productive biomes with a significant mix of fresh and salt water that support a rich biodiversity and serve as protected areas for many marine species. The correct answer is option c.
Step-by-step explanation:
Identifying a true statement about estuaries reveals an important aspect of marine biology. Estuaries are biomes where a source of fresh water, such as a river, meets the ocean, resulting in a unique ecosystem where fresh water and salt water mix to create brackish water. Due to this mixture, salinity in estuaries varies, significantly affecting the organisms living there. These environments provide critical protected areas for the spawning and growth of many marine species, such as crustaceans, mollusks, and fish, making estuaries some of the most productive and important biologically diverse regions on Earth.
Indeed, estuaries do not rank among the environments least affected by humans. In fact, they are often significantly impacted by human activities such as pollution, land development, and water resource management. Nor are they among the least productive environments; on the contrary, they are very productive due to the availability of nutrients brought by rivers and tidal waters, fostering a high level of biodiversity. While they may not necessarily have a higher biodiversity than rocky shores, estuaries are known for their rich biodiversity.
Therefore, the correct statement about estuaries is that they represent a close interaction between land and sea, where the dynamic mix of fresh and salt water creates an environment crucial for many species.