Question

what marine organism represents the vast majority of the oceans biomass?
plankton
crustaceans
shrimp
fish
sea cucumbers

Explanation:

Plankton are a diverse group of organisms that drift in water. They include phytoplankton (which perform photosynthesis) and zooplankton. Due to their vast numbers and widespread distribution in the ocean, they make up the vast majority of the ocean's biomass. Crustaceans (like crabs, lobsters), shrimp, fish, and sea cucumbers are all important marine organisms but their combined biomass is much less compared to the highly abundant and diverse plankton.

Answer:

Plankton