Here's why:

* Plankton are tiny organisms that form the base of the marine food web. They are primary producers, meaning they make their own food through photosynthesis.

* Dolphins are carnivores and feed on fish and other marine animals, which in turn feed on plankton. This means dolphins are secondary consumers or higher, depending on the specific food chain.

Therefore, dolphins are at a higher trophic level because they consume organisms that are at a lower trophic level (plankton).