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Some aspects of the intertidal ecology of marine organisms on Vancouver Island between Victoria and Port Renfrew. Widdowson, Thomas Benjamin

Abstract

The intertidal ecology of approximately seventy miles of coast, along the southwest shores of Vancouver Island from Port Renfrew to Victoria, was studied during the period from May 1957 until July 1958. This coast is a transition area between the open ocean at Port Renfrew and more sheltered waters east of Victoria, which are much freshened by the influx of the Fraser River. Attention was concentrated on the more conspicuous forms, mostly on those algae of the order Laminariales which do not occur in the more sheltered localities. Observations were made at twenty-six stations spaced along this coast. In collecting specimens, particular attention was given to those algae where identification is difficult or doubtful. These collections were made to complement the direct observations on those entities which could readily be identified in the field. The presence or absence of the entities studied was noted at each station. The distribution of some of the very conspicuous forms was determined along most of the coast between the stations. Any distinct upper or lower limits in the intertidal organisms at a station were recorded. Limited observations were made at fourteen other points, where these were needed to elucidate questions raised by the earlier data. Conditions of the physical environment, particularly of salinity, sea temperature, and tidal rhythms, were monitored at each of the stations wherever possible. Most of the twenty-six stations were occupied at least once each summer. Some of the more centrally located ones were visited at various times throughout the year in order to observe seasonal changes in the organisms and environmental conditions studied. When two or more measurements of the same upper or lower limit of an organism were made at different times, these replicates were used to calculate error in the technique used in finding the levels of these limits. The open coast forms penetrate varying distances along the coast into Juan de Fuca Strait in an easterly direction. Evidence is presented that different factors in the physical environment may be limiting for the geographical distribution of different organisms. Thirty-six vertical limits of the organisms studied are discussed. These are all the limits which were measured at nine or more stations throughout the area studied. The heights of each limit were plotted against the headland to headland distance between stations. Each limit was approximated by a line of least squares. The validity of this approach is discussed. The limits studied were grouped as follows: 1. Limits which are very variable throughout the area studied. 2. Limits which are more variable on the coast west of Sooke, than east of it. 3. Only slightly variable limits which have a definite slope downward from Port Renfrew to Victoria. 4. Only slightly variable limits which have no definite slope between Port Renfrew and Victoria. Various combinations of factors are suggested as explanations for these various types of limits. These factors include surf, light, desiccation, and nutrients, together with adult size and longevity of the organism. The theory of critical tidal factors is criticised. Species of the order Laminariales in this area which are as yet of questionable taxonomic status, are found in the following genera: Hedophyllum, Alaria, Costaria, Cymathere, and Laminaria. Of these, Hedophyllum and Alaria were studied in some detail. Hedophyllum was cultured from zoospores obtained from the sporophyte, through gametophyte stages, to what was presumably a young sporophyte of the same entity. The young sporophytes were not grown to stage where positive identification of secondary morphological characteristics was possible. The alternation of generations observed conformed to the pattern known for the other members of the Laminariales. Hedophyllum subsessile (Areschoug) Setchell, one of the two species of Hedophyllum reported from British Columbia, is reduced to synonomy under the other, H. sessile (C. Agardh) Setchell. A transitory stage in the development of H. sessile in its second season corresponds closely to the herbarium material on which Setchell appears to have based his description of H, subsessile. Variations in the bullation of the lamina of H. sessile are largely the result of environment, probably of exposure to, or shelter from, sunshine. Although the species of Alaria (A. marginata Postels and Ruprecht, A. nana Schrader, A. tenuifolia Setchell, and A. valida Kjellraan and Setchell) reported from British Columbia are very variable, they may usually be distinguished by the morphological characters of those sporophylls which are in a mature and fertile condition. These four species are therefore regarded as taxonomically valid in this study.

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