Complex sentence: These habitats include intertidal eelgrass beds, mudflats, and sandflats, which are covered by water during high tide and exposed to air during low tide, and also subtidal areas, which are covered by water almost all of the time.
Split into simpler sentences: These habitats include intertidal eelgrass beds, mudflats, and sandflats, and subtidal areas. Mudflats and sandflats are typically covered by water during high tide and exposed to air during low tide, while subtidal areas are covered by water almost all of the time.