Final answer:
Algal blooms caused by agricultural runoff are likely to result in less oxygen and less light in marine ecosystems. These changes create challenging conditions for aquatic life and can lead to dead zones where organisms cannot survive. Hence, the correct answers are option (a) and (c).
Step-by-step explanation:
Agricultural runoff can result in large blooms of algae in marine ecosystems. The changes in abiotic factors likely to be caused by an algal bloom include:
- Less oxygen in the water due to the respiration and decomposition of the algae.
- Less light penetrates through the water as the dense algal layers block sunlight, which is critical for the photosynthesis of other aquatic plants and the health of the ecosystem.
Algal blooms can create significant issues for aquatic life by altering these abiotic factors. When algae die, their decomposition further depletes oxygen levels in the water, creating dead zones where aquatic life cannot survive. Excessive algae do not directly affect the salt levels in the water, nor do they lower ocean temperatures, but they heavily impact oxygen levels and light penetration.