Final answer:
The threats to rising sea levels and coral bleaching are linked to climate change and human activities, not specific geographic locations. Increased temperatures, ocean acidification, and human impacts like overfishing and coastal runoff are the primary culprits affecting coral reefs. None of the provided options directly represent these threats.
Step-by-step explanation:
The major threats to rising sea levels and coral bleaching are significantly influenced by climate change and human activity. The increase in greenhouse gas emissions has resulted in warmer ocean temperatures, which affects marine biodiversity and causes disturbances like coral bleaching. Coral bleaching occurs when corals lose their symbiotic algae due to stress from elevated water temperatures, resulting in a loss of color and vitality. Additionally, rising carbon dioxide levels in the atmosphere lead to increased ocean acidity, which hampers the coral's ability to form its calcium carbonate structure.
This is coupled with human impacts such as sediment runoff from increased coastal development and overfishing that alters the balance of marine ecosystems. All of these factors contribute to the decline of coral reefs and the rich diversity they support, along with posing serious threats to coastal economies that rely on reefs for tourism.
Out of the options provided (A) Coastal Australia, (B) Fish populations in the Pacific, (C) Pacific trolls, and (D) New Zealand cities, the mention of 'Pacific trolls' does not represent a valid threat to coral reefs or rising sea levels. Therefore, the correct option in this context is not among the choices given. The provided options (A), (B), and (D) are all impacted by the aforementioned threats, but they are not in themselves threats. If the question aims to identify areas affected by these environmental issues, the concern should be focused on climate change, ocean acidification, overfishing, and coastal runoff which are major threats directly causing rising sea levels and coral bleaching.