Results:

Out of thirty-two total crabs found, twenty-six were of the H. sanguineus, and six were C. maenas. Thirteen H. sanguineus crabs were found in the low intertidal and thirteen were found in the mid-intertidal. Four C. maenas crabs were found in the low-intertidal while two were only found in the mid-intertidal. Most of these crabs were found in shallow pools and under medium sized rocks.

Figure 4: Proportions of H. sanguineus and C. maenas at the low and mid-intertidals. Overall, less C. maenus has a lower presence in Nahant, MA according to the proportions found.

By using a Chi-square test, the proportion of H. sanguineus and C. maenas in the rocky intertidal is significant (Chi-value = 12.5, P>0.004). This means that only 0.4% of the difference in the proportion of the species is by chance. The expected number of each crab species would be 16 since 32 total crabs were found in Nahant, MA (table 1). Looking only at the low intertidal, the proportion of  species was significant (Chi-value= 4.77, P>0.029). The mid-intertidal had significant values as well (Chi-value= 8.07, P>0.0045). 

 The difference between the body of both crab species is not statistically different in the low-intertidal zone (F= 0.04, P>0.845). Body size is also not  different in the mid-intertidal region (F= 0.27, P> 0.612).Combining values from low and mid zones, there is no statistical difference (F= 0.466, P> 0.500).