Final answer:
In a coral reef ecosystem, algae are responsible for photosynthesis and release oxygen as a byproduct. Algae are primary producers and work symbiotically with coral polyps, which alongside other creatures like fish are part of the broader ecosystem.
Step-by-step explanation:
In a coral reef ecosystem, the living thing responsible for releasing oxygen through the process of photosynthesis would be the algae. Algae, along with photosynthetic protists like dinoflagellates, are primary producers that convert light energy into chemical energy through photosynthesis, releasing oxygen as a byproduct. These primary producers form the base of the food web in aquatic environments.
Coral polyps have a symbiotic relationship with certain types of algae, such as the zooxanthellae, which live inside them and utilize sunlight to perform photosynthesis, benefitting both organisms. The parrot fish, which feed on these algae, and the barracuda, which feed on parrot fish, rely indirectly on the photosynthetic process for food but do not produce oxygen themselves. Therefore, the correct answer to which of these living things would be responsible for releasing oxygen from the process of photosynthesis is b. algae.