Final answer:
Sea anemones and algae have a mutualistic symbiotic relationship where both parties benefit: anemones receive nutrients from algae's photosynthesis, and algae utilize anemones' carbon dioxide.
Step-by-step explanation:
The interaction between a sea anemone and the algae that live inside the sea anemone is best described as a mutualistic symbiotic relationship. In this relationship, the sea anemones benefit from the food produced by the algae during photosynthesis, while the algae benefit from the carbon dioxide provided by the anemone, which is used in the process of carbon fixation. This type of relationship is crucial for both organisms' survival, particularly in nutrient-poor environments. Similar symbiotic relationships occur between corals and photosynthetic dinoflagellates called zooxanthellae, which are essential for the health of coral reefs by providing them with the necessary nutrients and energy to build their calcium carbonate skeletons.