Life Between Tide-Marks in North America. IVB. Vancouver Island, II

Abstract

Descriptions are provided of the distribution of algae and animals on rocky shores between tide-marks at four points in southeastern Vancouver Island, as seen in 1947, for comparison with the detailed account of Brandon Island given in Part IV A of this series. The zonation at all these places is then compared (p.236). The shore population of southeastern Vancouver Island inhabits coastal waters whose summer surface (monthly) means usually lie between 10 and 20 oC, and whose winter means do not fall to zero and rarely below 4.4 oC. Consequently winter ice is occasional and of little ecological importance. The salinity is more variable in some parts of the region than in others; at Race Rocks (near Victoria) ranging a little above and below 31%o (monthly means), in places more remote from the ocean between (for instance) 18.1 and 29.5%. The population is of a cold-temperate type, in many parts of the area showing characteristics associated with shelter from strong wave-action, but near Victoria (and on other comparable coasts) displaying a condition intermediate between the rough-water type found on the open Pacific coast of Vancouver Island, and the smooth-water type exemplified in Departure Bay. It develops a typical supralittoral fringe, a midlittoral in which barnacles, mussels and fucus and oysters are often important (and which in 1947 was subdivided into two to three subzones), and an infralittoral fringe which, when most typically developed, forms a Laminarian zone. The region is characterized by a rich population in which large speices (of both plants and animals) are particularly frequent, and echinoderms particularly numerous. In relation to the Pacific coast of North America as a whole, the population represents a more or less sheltered-water variant of one which has a very wide distribution on the open oceanic coast. The geographical extent and subdivisions of this are discussed on p. 239.