The Margin of the Sea

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From the upper reaches of the intertidal zone to the beginnings of terrestrial vegetation is a region of shoreline that is often sparsely inhabited by algae, and typically includes conspicuous expanses of bare rock. Inspection of the habitat reveals scattered or even abundant lichens, and often extremely patchy to extensive populations of macroscopic algae. The physiological ecology of photosynthetic algae in this part of the intertidal zone comprises the primary theme of this chapter. The organisms discussed here typically have extensive populations above mean high water neap tide (see Lüning, 1990; Lobban and Harrison, 1994; Little and Kitching, 1996, for introduction to tides and zonation). In general, these organisms are found exposed on bare rock and not in the rock pools where greater species richness occurs and less stringent environmental conditions are imposed. In terms of physiological constraints, the high intertidal and adjacent supratidal zone is among the most stressful encountered by organisms in general (Tomanek and Helmuth, 2002), and by marine macroalgae in particular (Davison and Pearson, 1996).

First, the rigors of the environment are explored, and then the various adaptive strategies of algae to survive and thrive in this habitat are discussed. Davison and Pearson (1996) reviewed stress tolerance in intertidal seaweeds as a whole; however, here the focus is on the upper intertidal zone and on disruptive stresses that cause damage or limit growth.