Aouth American intertidal systems and El Nino

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A study on the coastal ecosystems of central Peru was undertaken from 1999 to 2001. The study consisted of regular surveys of two main areas, Ancon and Paracas, and a series of intensive observations and sampling in austral summer in Ancon. Data from previous studies were also incororated in the present study. Oceanographic anomalies caused by El Nino phenomenan are considered to affect the dynamics of coastal fish species which are important for fisheries in this region (e.g.anchovy Engraulis ringens), but their influences on the shore ecosystems of low- to mid- latitude zones of South America are poorly known. Data on the long-term dynamics of major organisms on Peruvian rocky shores, in particular two species of starfish, Heliaster helianthus and Stichaster striatus, were gathered and analysed in relation to the occurrence of El Nino events. The two species demonstrated contrasting patterns of population fluctuation on both yearly and seasonal scales. Over a 10-ear period including El Nino years H.helianthus showed a declining population trend, while S.striatus showed an increasing trend with annual (seasonal) peaks in austral autumn/winter. On the other hand, starfishes' main prey, mussels, appeared to demonstrate a pattern of fluctuation which is different from the predators' patterns ut somewhat related to the occurrence of El Nino events. Continuation of this research including further analyses of available data will be fruitful and worthwhile.