the humboldt current system of northern and central chile - figema

MARTIN THIEL ET AL.storms delivered larvae of several gastropod species to the shore (Marín & Moreno 2002, C.A.Moreno in a personal communication to S.A. Navarrete).Few studies have directly and simultaneously examined the distribution of larvae in the plankton,physical processes and settlement onshore in the HCS. Even fewer have examined larval behaviourunder field or laboratory conditions (Poulin et al. 2002a,b, Manríquez et al. 2004, Vargas et al.2006a).Patterns of recruitment and benthic communitiesSystematic studies of recruitment of species in the HCS have focused on (1) characterising spatialand temporal variation in the arrival of new individuals for intertidal and a few subtidal species(e.g., Jara & Moreno 1983, Hoffmann & Santelices 1991, Stotz et al. 1991a, Camus & Lagos 1996,Martínez & Navarrete 2002); (2) relating these patterns with large-scale oceanographic anomalies,such as El Niño events (e.g., Moreno et al. 1998, Navarrete et al. 2002); (3) examining the effectsof recruitment variability on population dynamics and recovery of local populations from physical,biological or human-induced disturbance (e.g., Santelices & Ojeda 1984, Moreno et al. 1993b,Duarte et al. 1996, Alvarado et al. 2001); (4) determining the consequences of recruitment variationon the nature and intensity of species interactions in the adult habitat (e.g., Navarrete & Castilla1990, Moreno 1995, Navarrete et al. 2005, Wieters 2005); and (5) characterising the effects on theprocesses that regulate the dynamics of entire intertidal communities over large spatial scales(Navarrete et al. 2005).The far-reaching ramifications of persistent variation in recruitment have been most amplydemonstrated in recent studies that quantify patterns of recruitment over large temporal (years) andspatial (tens to hundreds of kilometres) scales. These studies are starting to shed light on, and findrecurrent patterns in, the causes of the typically large, baffling and usually ‘unpredictable’ variationin coastal ecosystems. Studies along the California coast have found large-scale regularities inpatterns of recruitment of sessile species that can help reconcile odd experimental results (Mengeet al. 1994, Connolly et al. 2001, Menge et al. 2003). Studies in the HCS conducted by Navarreteet al. (2002, 2005) have evaluated the effects of variation in wind-driven upwelling on communityregulation along 900 km of coastline between 29°S and 35°S during 72 months. Sharp discontinuitiesin upwelling regimes around 30–32°S produced abrupt and persistent breaks in the dynamicsof benthic and pelagic communities over hundreds of kilometres (regional scales) (Figure 15A,B).Rates of mussel and barnacle recruitment changed sharply at 32°S, determining a geographic breakin adult abundance of these competitively dominant species. Analyses of satellite images alsocorroborate the existence of regional-scale discontinuities in dynamics and concentration of offshoresurface chl-a that had been previously described at coarser resolution (Thomas 1999, Thomas et al.2001b). Intertidal field experiments showed that the paradigm of top-down control of intertidalbenthic communities (Castilla & Durán 1985, Paine et al. 1985, Castilla 1999, Navarrete & Castilla2003) holds only south of this geographic discontinuity. To the north, populations seem recruitmentlimited, and predators have negligible effects, despite attaining similarly high abundances. Thus,geographically discontinuous oceanographic regimes set bounds to the strength of species interactionsand define distinct regions for the design and implementation of sustainable managementand conservation policies along the HCS. Further ecological studies using molecular markers areneeded to define the consequences of this variation for the genetic population structure of musselsand barnacles, as well as for other components of intertidal communities, many of which do notexperience such a discontinuity in recruitment, despite having similar life histories and generalbiology (Figure 15C,D).250