How many samples would it take to detect a change in Q. fragosa density based on quantitative sampling?

Currently in our monitoring we take 100 0.25 m2 quadrats at our sampling locations which allows us an 80% chance of detecting a 30% decrease in the entire mussels population size with 80% confidence.
- This is with a density 1000 times that for Q. fragosa alone

To have a similar level of confidence for changes in Q. fragosa we would have to take 16,750 0.25 m2 quadrats

Currently in our monitoring we take 100 0.25 m2 quadrats at our sampling locations which allows us an 80% chance of detecting a 30% decrease in the entire mussels population size with 80% confidence.