Final answer:
The initial step in an investigation of clownfish by a marine biologist would be to identify a question based on observations, such as asking what factors are contributing to a population decline.
Step-by-step explanation:
A marine biologist concerned about clown fish in a section of the coral reef will begin an investigation of the clown fish by performing the first step of the inquiry process which is identifying a question based on observations. This step involves formulating a specific question that the marine biologist wants to answer about the clownfish population. For example, the biologist may observe that the number of clownfish is declining and pose the question: "What factors are contributing to the decline of clownfish in this particular section of the coral reef?" Potential factors could include changes in the reef ecosystem, water quality issues, or disruptions in the symbiotic relationship between clownfish and anemones.