Defining Ocean Boundaries: Coastline, Continental Shelf, or Abyssal Plain?

There is no single, universally agreed line where the ocean “starts and stops.” Different disciplines use different boundaries:

Legal/Political

Coastline / Baseline – defines territorial sea, EEZ, continental shelf claims (UNCLOS).

Ecological

Continental Shelf Edge (~200 m depth) – transition from neritic to oceanic ecosystems; most marine biomass.

Geological

Abyssal Plain / Continental Rise – true deep-ocean floor; crustal type changes (continental vs. oceanic).

Practical

Mariners use charted boundaries; scientists define study regions by research questions.

The ocean is a continuous global system; boundaries are human constructs for management and study.