What characteristic defines filamentous algae in aquatic ecosystems?

Filamentous algae are characterized by their ability to form dense mats, which can exhibit a slimy or coarse texture. This growth habit allows them to occupy significant areas on the surface of water bodies, particularly in shallow environments where sunlight is abundant. These mats can create a habitat for a variety of organisms and may impact the overall health of aquatic ecosystems by altering light penetration and oxygen levels.

The presence of a slimy or coarse texture is a crucial aspect of filamentous algae. This characteristic not only makes them recognizable but also influences their interactions with other species in their environment. Their growth patterns and textures contribute to their role in nutrient cycling and can affect water quality and clarity.

Other options describe traits that do not accurately reflect filamentous algae. For example, a smooth texture would not be representative of their physical structure. Additionally, while some filamentous algae may remain submerged, many can grow in varying water depths and might be found floating near the surface. Lastly, while certain types of algae thrive in saltwater environments, filamentous algae are not limited to saltwater and can be found in freshwater ecosystems as well. Therefore, the defining characteristic remains their formation of dense mats with a distinctive texture.