Sea level and Sea-level

Sea level noun - Level of the ocean's surface (especially that halfway between mean high and low tide); used as a standard in reckoning land elevation or sea depth.

Sea-level and sea level are semantically related. In some cases you can replace phrase "Sea-level" with "Sea level", this phrases are similar.

Sea-level adjective - Lying below the normal level.

Sea level and sea-level are semantically related. You can use "Sea level" instead a noun phrase "Sea-level".