Scope

Between the lowest and highest reaches of the waves on rocky coasts lives a rich array of sedentary invertebrates and algae (see also Rocky Intertidal Zone). The most abundant species often occur as separate horizontal bands, each limited to a different segment of the range of the tides (Figures 1 and 2). Understanding the causes of intertidal zonation is one of the oldest and most intensively studied problems in ecology. The dense populations, comprised of relatively small individuals with brief life cycles, fall along comparatively compressed spatial gradients in physical conditions. This arrangement presents ecologists with opportunities for experimental studies of population limitation that would be costly or impractical in other biomes. Therefore, intertidal

Figure 1 A seaward view of zonation on a wave-exposed shore in Barkley Sound, British Columbia (48°53' N,125°20' W). The foreground shows relatively high shore levels with a patchy zone of acorn barnacles Chthamalus fissus (beige patches) and the small red algae Mazzaella cornucopiae (ochre patches). The center ground shows mid-shore levels with a dense bed of the mussel Mytilus californianus (dark gray) and patches of the acorn barnacle Semibalanus glandula (beige). Upper center ground shows low shore levels covered by beds of the kelp Egregia menziesii and patches of surfgrass (Phyllospadix sp.). The separation of the meter tapes (white parallel lines) is approximately 1 m. The three zones correspond to the upper eulittoral, lower eulittoral, and infralittoral fringe classifications described in the text. Photograph taken on an unusually calm day. Photo by C. Robles.

Figure 1 A seaward view of zonation on a wave-exposed shore in Barkley Sound, British Columbia (48°53' N,125°20' W). The foreground shows relatively high shore levels with a patchy zone of acorn barnacles Chthamalus fissus (beige patches) and the small red algae Mazzaella cornucopiae (ochre patches). The center ground shows mid-shore levels with a dense bed of the mussel Mytilus californianus (dark gray) and patches of the acorn barnacle Semibalanus glandula (beige). Upper center ground shows low shore levels covered by beds of the kelp Egregia menziesii and patches of surfgrass (Phyllospadix sp.). The separation of the meter tapes (white parallel lines) is approximately 1 m. The three zones correspond to the upper eulittoral, lower eulittoral, and infralittoral fringe classifications described in the text. Photograph taken on an unusually calm day. Photo by C. Robles.

Figure 2 A shoreward view of zonation on a shore protected from wave action on Santa Catalina Island, California (33°25' N, 115°30' W). The lowest shore levels just above the waterline are covered by brown algae, Eisenia arborea, Halidrys dioica, and Sargassum muticum. Mid-shore levels are covered by an algal turf, the intertwined thalli of Chondracanthus canaliculatus and Corallina pinnatifolia, overlain in spots by the globular thalli of Colpomenia sinuosa. The highest zone is the fucoid algae Silvetia deliquescens (ochre band). The distance along the surface from waters edge to the top of the Silvetia is approximately 3.5m. Photograph by C. Robles.

Figure 2 A shoreward view of zonation on a shore protected from wave action on Santa Catalina Island, California (33°25' N, 115°30' W). The lowest shore levels just above the waterline are covered by brown algae, Eisenia arborea, Halidrys dioica, and Sargassum muticum. Mid-shore levels are covered by an algal turf, the intertwined thalli of Chondracanthus canaliculatus and Corallina pinnatifolia, overlain in spots by the globular thalli of Colpomenia sinuosa. The highest zone is the fucoid algae Silvetia deliquescens (ochre band). The distance along the surface from waters edge to the top of the Silvetia is approximately 3.5m. Photograph by C. Robles.

zonation has served historically as a test bed for theories of population and community regulation.

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