Results

              Carcinus maenas were found to be the dominant crab species in rocky intertidal area, making up 77.4% of the crabs collected in the quadrats.  C. maenas and H. sanguineus were the only species of crabs uncovered in the quadrats.
 

Here is the raw data

            Figure 1) Percentage of each species by tidal height.  This is simply comparing the proportions of individuals of each crab species found at one particular tidal height, pooling data from all dates.

 

Figure 2) Categories of quadrats.  All 37 quadrats are accounted for in this figure and are classified by the presence or absence of either species.

Figure 3) Average carapace size at the different tidal heights.  While Hemigrapsus sanguineus’s average size does not change significantly at the tidal heights it was found in, Carcinus maenas’s average size increases with decreasing tidal height and then drops substantially at the lowest tidal height.  This indicates a significant decrease in the crab’s fitness at 1.5 m from the low tide mark.

            Table 1) Chi square values for crab distributions.  The critical value at one degree of freedom with a p value of 0.005 is 7.88.  With the obtained chi square value of 18.24, the species distributions are very significant and the crabs are certainly not randomly distributed along the intertidal.

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