Answer:
mutualism
Step-by-step explanation:
Mutualism is a type of symbiotic relationship between two organisms in which both benefit and neither is affected negatively in any way.
Mutualism can be in the form of resource-resource when it involves an exchange of resources between the organisms, service-resource when a resource is being swapped for a service or, service to service when it involves exchange of services between the two organisms.
In this case, the clownfish offers protection service to the sea anemone while the sea anemone in turn also offers protection to the clownfish. This is a service-service mutualism.