What term is used to describe any living thing in an ocean?

The term "marine organism" specifically refers to any living thing that resides in the ocean. This includes a vast array of life forms, such as fish, mammals, invertebrates, plants, and microorganisms, all of which play a vital role in the marine environment. By utilizing the word "marine," it captures the essence of life specifically adapted to oceanic conditions, encompassing both the organisms and their interactions within that particular habitat.

In contrast, "aquatic habitat" refers to the environments where water is present, which encompasses both freshwater and saltwater locations, and does not exclusively denote organisms. The phrase "estuary life" pertains specifically to the organisms found in estuaries, which are partially enclosed coastal bodies of water where freshwater from rivers meets and mixes with saltwater from the sea. While part of the marine ecosystem, it is a more defined and limited context. "Oceanic ecosystem" describes a broader system of interactions among living organisms and their environment in the ocean, rather than a specific term for living organisms alone. This term encompasses various species and their relationships, but it does not focus solely on individual living entities.