Final answer:
An algal bloom in the ocean can be caused by the interaction of the water and nitrogen cycles. Nitrogen and phosphorus contribute to the growth of algae, and when there is a large input of these nutrients, an algal bloom occurs. Algal blooms reduce light penetration, deplete oxygen, and can result in the death of aquatic organisms.
Step-by-step explanation:
An algal bloom in the ocean can be caused by the interaction of the water and nitrogen cycles. Nitrogen and phosphorus, which are important limiting nutrients in lakes and ponds, contribute to the growth of algae. When there is a large input of nitrogen and phosphorus, such as from sewage and runoff from fertilized lawns and farms, the growth of algae skyrockets, resulting in an algal bloom. Algal blooms reduce light penetration in the water, make the water aphotic, and prevent photosynthetic plants from surviving. When the algae die and decompose, severe oxygen depletion occurs, leading to the death of fishes and other oxygen-dependent organisms.