Final answer:
Salinity is the most important abiotic factor for sustaining life in marine biomes.
Step-by-step explanation:
The most important abiotic factor for sustaining life in marine biomes is salinity. Organisms living in marine biomes have adapted to thrive in saltwater environments, and changes in salinity can have significant impacts on their survival. For example, if the salt concentration increases significantly, organisms that cannot tolerate high salt levels may not survive. Salinity also affects the osmotic balance of marine organisms.