PLANT AND ANIMAL ASSOCIATIONS 47 



semi-marine, (d) the Verrucaria maura belt, normally occupy- 

 ing the shore between high neap and high spring tides, and 

 {e) a belt of marine Verrucariae, marine encrusting species 

 submerged by the tide each day. 



Finally, at the seaward margin of the shore is found the 

 great Association of the Tangle weeds, Laminaria, only un- 

 covered by spring tides, and accompanied by a rich fauna 

 (see Plate X). 



In addition to the horizontal zoning above described, 

 there exists on the shore a distinct vertical stratification, 

 affecting both the plants and animals. We find species of 

 plants and animals forming associations of varying heights 

 above and below the general surface level (just as in a wood 

 there are species on and under shrubs and trees, each showing 

 sub-types), while epiphytic species may be found on all. 

 Similarly, the animals inhabiting the sea-shore show both 

 horizontal and vertical zoning. Different assemblages of 

 animals accompany the different algal zones and associations, 

 while there are distinct animal associations and communities 

 of mud and sand attached to rocks or boulders, or boring 

 into rocks ; living among algse ; free-swimming, or floating ; 

 all with their distinct and typical features. Some examples 

 will be given shortly. 



Numbers of Shore Population. — As to the actual 

 number of species found within tide-marks, it is exceedingly 

 difficult to give any accurate data, most enumerations of 

 local faunas extending much deeper than low-water mark. 

 Some of the faunas are extremely rich in species : Whitelegge 

 (1889) enumerated 2136 species for Sydney Harbour ; the 

 Irish Sea yielded over 1680 species of Invertebrates ; 

 Trieste, 1268 (Dr. Graafe), and Woods Hole the same 

 (Sumner, 191 3), while 1213 were recorded for the Firth 

 of Forth (Evans, 1909), etc. 



Undoubtedly by far the largest number of the species 

 inhabiting the tidal region occur between the limits of low- 

 water neaps and low- water springs. The species able to 

 endure exposure to air every twelve hours are comparatively 

 few in number (although there are a small minority that 



