II. Biological Diversity
One reason that rocky shores have received such keen scientific attention, particularly in the MBNMS region, is because of their extensive biological diversity that is often highly structured. Assemblages of species (sensu Underwood and Petraitis 1993) grow in distinct zones that vary with tidal height, wave exposure, and a variety of other physical and biological phenomena (the more common species are discussed below; see III. Distribution Patterns and Table 1). Moreover, epibionts and complex assemblages of less obvious species are associated with the wide array of dominant species (D'Antonio 1985, De Vogelaere 1991, 1993, Lohse 1993a). The upper intertidal alga, Endocladia, can have at least 93 different species associated with it (Glynn 1965) and mussel beds can contain over 300 associated taxa (Suchanek 1979, 1992). Detailed species lists have been developed for many sites within the MBNMS (Table 2)
and these have been made possible, in part, by the excellent taxonomic keys developed for the region [invertebrates: Smith and Gordon (1948), Smith and Carlton (1975), Morris et al. (1980); algae: Abbott and Hollenberg (1976), Dawson and Foster (1982); fishes: Miller and Lea (1972), Fitch and Lavenberg (1975), Eschmeyer et al. (1983)]. The physical setting of the MBNMS region may explain the relatively high biodiversity found on its rocky shores: substantial tidal range (2.3 m), upwelling of nutrient-rich water, and fog associated with upwelling that prevents desiccation during low tides in otherwise dry summer months (Foster et al. 1988; and see Physical Oceanography, Climate and Meteorology, and Chemical Oceanography sections).
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Rocky Intertidal Habitats - Table of Contents