Final answer:
In a coral reef ecosystem, sediments, saltwater, sunlight, and water temperature are the abiotic factors. Sunlight is the most crucial abiotic factor for sustaining life in marine biomes. The intertidal zone is where organisms are alternately exposed to air at low tide and submerged at high tide.
Step-by-step explanation:
The abiotic factors in a coral reef ecosystem include several non-living components that influence the environment and the organisms within it. The abiotic factors listed in the student's question are 1. Sediments, 2. Saltwater, 3. Sunlight, and 4. Water temperature. Each of these plays a crucial role in sustaining life within the marine biome. Sediments can affect water clarity and which organisms can thrive, while saltwater composition is essential for the osmoregulation of marine life. Sunlight is critical for photosynthesis, which is the base of the food web, and water temperature influences metabolic rates and the distribution of species.
Concerning the most important abiotic factor for sustaining life in marine biomes, sunlight is key as it provides energy for photosynthesis which supports the food chain. Various marine zones exist, and the zone where organisms are exposed to air and sunlight at low tide but are underwater most of the time, especially during high tide, is known as the intertidal zone.