Final answer:
Red algae can live at great depths with little light due to their ability to use red light for photosynthesis and their adaptations to low-light environments.
Step-by-step explanation:
Red algae are able to live at great depths where there is very little light due to their ability to utilize red light for photosynthesis and their adaptations to low-light environments. Red light penetrates deeper in the water column, allowing red algae to carry out photosynthesis at greater depths than other algae. Additionally, red algae possess phycobiliproteins pigments that can capture and utilize red light. These adaptations enable red algae to survive and serve as the base of food chains in cooler marine and freshwater habitats.