Final answer:
The mutualistic relationship between corals and algae in photic zones primarily serves to enhance nutrient availability and energy production for the corals, enabling their survival in nutrient-poor waters.
Step-by-step explanation:
Corals have a mutualistic relationship with photosynthetic algae in the photic zones of water. This relationship serves to provide increased nutrient availability and d) improved energy production through photosynthesis for the corals. The algae, known as zooxanthellae, benefit by residing in a protected environment provided by the coral polyps. These polyps, in turn, receive nutrients and energy from the algae, which are essential for the coral's survival, particularly in nutrient-poor waters. The symbiotic process also contributes to coral reef formation, a critical ecosystem in marine habitats. Without the presence of zooxanthellae, corals are prone to bleaching and may die, as they rely heavily on the sugars produced by algae through photosynthesis.