Final answer:
The shallow water area of a fringing coral reef is most likely to be affected by sedimentation, particularly the back reef or lagoon areas, due to the necessity of sunlight for the photosynthetic algae that symbiotically live within the coral.
Step-by-step explanation:
The area of a fringing coral reef most likely to be affected by sedimentation is the shallow water. Sedimentation typically occurs when sediments are deposited by water, often heightened by activities such as coastal development or agricultural runoff.
These sediments can smother coral reefs, blocking sunlight and hindering the photosynthesis of the symbiotic algae, known as zooxanthellae, that live within the coral. Because these algae provide essential nutrients to the corals through photosynthesis, sedimentation poses a significant threat in shallow waters where light penetration is crucial for photosynthetic processes. Moreover, the back reef or lagoon areas behind the reef may also be highly susceptible due to low wave activity that can lead to sediment accumulation.
Considering the habitat requirements of coral reefs, they are primarily found in shallow ocean water (option a.), within the photic zone where sunlight is available for the photosynthetic algae. Coral reefs are vital marine ecosystems, characterized by high biodiversity, but they face numerous human-induced threats, including sedimentation, that can lead to detrimental effects on these complex structures.