This is the 3613th most frequent Spanish word.
marino
"Marino" means "marine" or "related to the sea" in English.
In this sentence, 'marino' is used as an adjective modifying 'biólogo' to describe a professional field related to marine life.
El biólogo marino estudia las criaturas del océano.
The marine biologist studies ocean creatures.
Here, 'marino' is used as an adjective describing 'barco', meaning something associated with the sea or marine activities.
El barco marino navegó cerca de la costa.
The marine ship sailed near the coast.
In this case, 'marino' functions as a noun referring to a person who works on a ship or is involved in sailing.