A Survey of the Distribution of Intertidal Algae Along a Coast Transitional in Respect to Salinity and Tidal Factors

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Abstract
The dominant intertidal organisms studied in this survey were mostly brown, red, and green algae, together with a few species of marine flowering plants, barnacles, and molluscs. The flora of the northern shores of Juan de Fuca Strait show a transition between the flora of the open coast around Port Renfrew in the west, and that of the semi-sheltered coast near Victoria in the east.The differences between the flora of Port Renfrew and that of Victoria can be studied as boundaries; the eastern boundaries of species occurring at Port Renfrew but not at Victoria, and the western boundaries of species occurring at Victoria but not at Port Renfrew. Fourteen eastern (inner) boundaries of open coast organisms, and four western (outer) boundaries of sheltered coast forms were found to be concentrated in the vicinities of Port Renfrew, Victoria, and Sooke, half way between.Along Juan de Fuca Strait, Port Renfrew is the easternmost locality with a completely open coast environment, characterized by a salinity usually above 32‰. Sooke is the easternmost locality where water of 32‰ is found with some degree of frequency, probably as a result of upwelling associated with strong westerly winds. Victoria is the outermost locality where water of appreciably less than 30‰ may occur, because of heavy runoff from the Fraser River.The author studied the vertical distributions of organisms by measuring upper and lower limits at 34 stations along the coast, plotting the heights obtained, and calculating regression lines for the points plotted. These limits were of four types: A. very variable along the whole coast; B. more variable between Port Renfrew and Sooke than between Sooke and Victoria; C. slightly variable, with a slope down from Port Renfrew to Victoria; and D. slightly variable, with little or no slope.The slightly variable limits (C and D above) were used as a test of the theory that tidal factors can be used to explain, or at least describe, the vertical limits of intertidal organisms. The coast between Port Renfrew and Victoria shows a transition between a mixed semi-diurnal tide in the west and a diurnal tide in the east. Thus, the heights of the various tidal factors are usually different at Port Renfrew, Sooke, and Victoria, because of the different nature of the tides. The heights of most limits failed to correspond to the same tidal factor at these three places. The different patterns of variation and slope, found in the limits generally, indicate that it is unlikely that any other theory can provide a simple explanation of the height of most intertidal limits.

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