Final answer:
A tuna is an example of a tertiary consumer as it is a carnivore that preys on other carnivores within a food chain or web. They are crucial for maintaining ecological balance by managing populations of other organisms.
Step-by-step explanation:
An example of a tertiary consumer is an organism that occupies a high trophic level by feeding on other carnivores. In an ecosystem, this can include animals like large predators that have few or no natural enemies. Within food chains or webs, tertiary consumers play a critical role as they help maintain the balance by controlling the populations of other species, including secondary consumers.
Considering the options provided, A. Tuna is an example of a tertiary consumer, as it is a carnivore that often consumes other carnivores in the ocean. Tuna feeds on smaller fish, which may themselves be carnivorous, thereby placing tuna higher up on the trophic levels.
If a tertiary consumer becomes extinct, it could lead to an imbalance in the ecosystem such as overpopulation of lower trophic level species, which may result in the overconsumption of producers and eventually a collapse of the food web.