Which aquatic ecosystem would be characterized by higher salinity levels?

The correct answer identifies marine environments as ecosystems with significantly higher salinity levels compared to the other options. Marine environments, such as oceans and seas, typically contain salt concentrations averaging around 35 parts per thousand. This elevated salinity is a fundamental characteristic of these ecosystems, influencing their biology, chemistry, and the types of organisms that can thrive there.

In contrast, freshwater lakes have minimal salinity, often less than 1 part per thousand, making them unsuitable for saltwater species. Estuaries, while they do have some salinity due to the mixing of freshwater from rivers and saltwater from the ocean, generally have lower salinity levels than fully marine environments. Wetlands can exhibit a range of salinity levels, but they tend to be lower than those found in marine environments, with many wetlands being freshwater systems.

The high salinity of marine environments plays a crucial role in defining the ecosystems, as many marine species have adapted to survive in these salty conditions, providing a diverse array of life that is unique to this habitat.