Question

what is a major threat to coral reefs? existing biodiversity pollution and climate change stable environment natural fish waste

Explanation:

Pollution can harm coral - dwelling organisms and change water quality. Climate change causes ocean acidification and warming, leading to coral bleaching and death. Other options are not threats. Existing biodiversity is part of a healthy reef, a stable environment is beneficial, and natural fish waste is a normal part of the ecosystem.

Answer:

pollution and climate change