Step 1: Understanding marine zones.
Marine environments are classified by depth: Littoral (intertidal), Neritic (continental shelf), Bathyal (continental slope), and Abyssal (deep ocean floor).
Step 2: Identification.
The littoral zone lies between high and low tide marks — the shallowest zone directly influenced by tides.
Step 3: Conclusion.
Thus, the Littoral zone is the shallowest marine environment.