Answer:
Crabs, mussels, and limpets compete for the same producer
Step-by-step explanation:
Competition is where the same organisms use the same resources in an environment. In this food web, by looking at the arrows pointing away from the producers (organisms that produce their own energy, often through photosynthesis), you can see what eats them. The algae has three arrows pointing away from it and towards these three organisms, hence your answer. Hope I could help :)