Historically, there has not been much interest in funding and publishing research on temporal variability in rocky shores, so there has been relatively little work on this topic. Moreover, long-term studies cannot be completed in the standard dissertation project time scale, especially when some species of interest, such as the alga Petrocelis, may live 90 years or more (Paine et al. 1979). However, understanding short and long-term natural variability is essential for assessing MBNMS "health" and to prepare for natural resource damage assessment (NRDA). Some of best information on temporal change is available from agency monitoring studies associated with power plant outfalls (e.g. Pacific Gas and Electric Company 1984) and in preparation for assessing potential human impacts (Minerals Management Service 1992; and see Table 2).
Even with limited information, seasonal, between year and long-term changes clearly exist in rocky shore assemblages. Seasonal patterns in intertidal assemblages include the removal of upright portions of algae and patches of animals during winter storms, bleaching and killing of algae when low tides coincide with hot days in the Summer and Fall, cycles of reproduction and growth related to seasonal changes in temperature and photoperiodic, and seasonal availability of larvae associated with upwelling events (Foster et al. 1988, 1991). With the possible exception of fish assemblages (Yoshiyama et al. 1986), rocky intertidal assemblages appear to have less interannual than seasonal variation (Foster et al. 1988, Kinnetic Laboratories Inc. 1992). At the time scale of decades, anecdotal observations indicate that the entire assemblage of species on a rocky shore may change with processes such as flash floods (Littler and Litter 1987), re-population of top predators such as sea otters in Monterey Bay , and changes from algal-dominated assemblages to sand-encrusted aggregations of polychaetes (Foster et al. 1988, 1991). In a rare time scale study of 60 years, Barry et al. (1995) noted changes in animal species composition at Hopkins Marine Station consistent with predictions of change associated with global warming. At this time scale, it is difficult to determine the causes of changes, but sea level rise and fall, long term cyclic changes in tides, catastrophic disease, variations in flow of offshore currents, cataclysmic geologic disturbances and slower weathering are the backdrop needed to assess resource management evaluations and decisions.
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