Why Is the Biome Concept Difficult to Apply to Aquatic

Why is the biome concept difficult to apply to aquatic systems?

A) Temperature is similar over the majority of aquatic biomes, unlike terrestrial systems.
B) Aquatic communities vary little from place to place because of the ability of fish to travel between oceans.
C) Nutrients from terrestrial biomes limit most aquatic systems, so terrestrial systems must be considered when determining the aquatic biomes.
D) Producers in many aquatic systems are algae, which have little characteristic large-scale structure.