E. 31. Kindle — Bottom Control of Marine Faunas. 457 



Fig. 3A shows the vertical face of an intertidal ledge with 

 a deeply etched surface, — a type of surface which is apt to 

 shelter the maximum amount of intertidal gasteropod life. 

 Parts of the surface seen in the photograph show more than 

 100 gasteropods to the square foot. 



Let us compare this stony beach at Digby as a habitat for 

 invertebrate life with another type of beach which is very com- 

 mon about the Bay of Fundy. At the mouth of the Avon 

 River an island about 3^ miles in length and half a mile in 

 width is exposed at low tide. This island, which is composed 

 entirely of sand, is covered at high tide by from 10 to 25 feet 

 of water. The strong tidal currents keep the surface of the 

 sand constantly shifting during ebb and flow. The backward 

 and forward drift of the sand makes it impossible for marine 

 life to establish itself here. This type of drifting sand surface 

 is shown in fig. 2B. I did not find a single living shell on the 

 island and only 3 or 1 dead shells were seen. The surface 

 appears to be as barren of life as a desert of sand in an arid 

 climate would be. The striking contrast between this barren 

 sandy beach and the rocky beach at Bear Island, where nearly 

 every square yard is occupied by scores of shells, as a habitat 

 for marine life is clearly clue entirely to the different character 

 of the materials comprising the two beaches. The barren 

 character of this intertidal sand island also furnishes a striking 

 contrast to the rich fauna of the hard gravelly and stony bot- 

 tom of the channel immediately east of it. From this bottom 

 a few rods east of the island the species listed in column ten 

 of the table were taken as well as a variety of other forms of 

 life including sponges, making a total of more than 25 species. 

 A single haul of the dredge would sometimes bring up a bushel 

 of sponges from this bottom. The soft grey or chocolate- 

 colored mud beaches which are common about the Bay of 

 Fundy represent another type of the intertidal zone on which 

 molluscan life is rare. These grey muds contain very little 

 organic matter and are quite different from the black mud of 

 station 2 which is rich in organic matter. The mud facies of 

 the intertidal zone is shown in fig. 2A. 



Comparison of the poverty stricken molluscan fauna of soft 

 grey muds or the lifeless drifting sand facies of the intertidal 

 zone with the teeming life of the rocky beaches (see fig. 3) 

 furnishes incontestable evidence of the paramount influence of 

 the physical character of the bottom materials in determining 

 the abundance and kind of marine life living on them. On 

 rocky shores a single species of barnacle, Balanus balenoi'/es, 

 is sometimes represented by 3000 individuals to the square 

 foot. The bottom control of faunas which is so easily observed 

 in the intertidal zone is equally potent below low tide as I 

 have already shown. The dependence of the oyster upon solid 



