Final answer:
A biotic factor in a coral reef ecosystem includes the corals themselves and the symbiotic algae they harbor. Corals are considered a foundation species that significantly contribute to the ecosystem's biodiversity and species richness.
Step-by-step explanation:
The student's question pertains to the identification of a biotic factor in a coral reef ecosystem. Biotic factors are the living components of an ecosystem, such as plants, animals, bacteria, and fungi. In the context of coral reefs, the corals themselves are a key biotic factor, as they provide structure and habitat for a multitude of other marine organisms and engage in a symbiotic relationship with algae, which are also a biotic factor.
For example, zooxanthellae, a type of algae found within the corals, supply the coraals with nutrients through photosynthesis in return for protection and access to sunlight. This symbiotic relationship is crucial for the health and sustainability of coral reef ecosystems. Coral is often considered a foundation species due to its ability to extensively influence the species richness and biodiversity of the ecosystem it inhabits.