Discussion:

Pool A (picture) was the largest pools examined. Algae cover was dense and the Pool A included many rocks for crabs to hide under. The largest crab recorded for this study was found in Pool A, a Hemigrapsus with a body width of 49.42mm. The pool contained a wide variety of organisms, including mussels and smaller crabs, potential prey items for the large hemigrapsus. The three other crabs recorded in the pool on 9/28 were of average size. The size of the pool did not appear to have any affect on the water temperature when compared to the other tide pools on both 9/28 and 11/14.

The data recorded suggests that larger crabs with a body width equal or greater than 30mm would be more frequent in larger tide pools with a depth of greater than 15mm. There appeared to be no preference regarding the tidal zones in this study. There were no large specimen of Cancer found. However, large Cancer shells were found in Nahant and Rye indicating that Cancer was a prey item. On the 11/14 trip, three large Cancer shells were found in Pool D.

In the 11/12 data from Rye and the 11/14 data from Nahant, the total number of crabs was down from the 9/28 data. This correlates with the drop in temperature in the tide pools and onset of winter. The total number of Carcinus recorded was significantly greater than Cancer or Hemigrapsus for this study.

Rye offered geographic differences when compared to Nahant. The gradient at Rye was much more gradual than at Nahant. The rocky inter tidal consisted of many small rocks with smooth surfaces with a few large rock formations and fewer tide pools than found in Nahant. Some pools observed were long and narrow, extending from the mid-inter tidal zone down directly into the ocean.

It seems likely that larger crab would be found in tide pools in order to feed. Mussels are a prey item of crab, as are smaller crab. Crab also tend to prey on smaller mussels, found within tide pools, as opposed to larger mussels to reduce damage to claws (6). Larger crab may not have this concern and leave the inter tidal zone for the water.

There could be a theoretical limit to the size of a crab who enter tide pools for food (2, 3, 4). The largest observed crab were the three dead Cancer that were likely victims of avian predators. Large crab may be easy prey items considering their size and lack of suitable shelter from birds.

Further study would be helpful, including a look at which organisms located in specific tide pools could be considered prey items for crab and attempting to capture the crab over a periods of months as opposed to three single field studies.