紅藻, or red algae, are a group of marine plants found primarily in ocean waters. They are characterized by their reddish color, which comes from the pigment phycoerythrin. This pigment allows them to absorb light at greater depths, enabling them to thrive in various underwater environments. These algae play a crucial role in marine ecosystems, providing food and habitat for many marine organisms. Additionally, some species of 紅藻 are harvested for their commercial value, being used in products like agar and carrageenan, which are common in food and cosmetic industries.