The answer is (a), site A.

The relative abundance of fish and shellfish at each site is calculated by summing the product of the area of each habitat type times the relative abundance of the fish and shellfish in each habitat type.

For site A, the relative abundance of fish and shellfish = (0.25 × 25) + (0.25 × 6) + (0.25 × 3) + (0.25 × 1) = 8.75.

For site B, the relative abundance of fish and shellfish = (0.5 × 25) + (0.5 × 1) = 13.

Since site A supports about two thirds (8.75 ÷ 13 = 0.67) the number of fish and shellfish as site B, altering site A would have less impact than that of site B on fish and shellfish abundance.