MARTIN THIEL ET AL.storms delivered larvae <strong>of</strong> several gastropod species to <strong>the</strong> shore (Marín & Moreno 2002, C.A.Moreno in a personal communication to S.A. Navarrete).Few studies have directly <strong>and</strong> simultaneously examined <strong>the</strong> distribution <strong>of</strong> larvae in <strong>the</strong> plankton,physical processes <strong>and</strong> settlement onshore in <strong>the</strong> 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 <strong>of</strong> recruitment <strong>and</strong> benthic communitiesSystematic studies <strong>of</strong> recruitment <strong>of</strong> species in <strong>the</strong> HCS have focused on (1) characterising spatial<strong>and</strong> temporal variation in <strong>the</strong> arrival <strong>of</strong> new individuals for intertidal <strong>and</strong> a few subtidal species(e.g., Jara & Moreno 1983, H<strong>of</strong>fmann & Santelices 1991, Stotz et al. 1991a, Camus & Lagos 1996,Martínez & Navarrete 2002); (2) relating <strong>the</strong>se patterns with large-scale oceanographic anomalies,such as El Niño events (e.g., Moreno et al. 1998, Navarrete et al. 2002); (3) examining <strong>the</strong> effects<strong>of</strong> recruitment variability on population dynamics <strong>and</strong> recovery <strong>of</strong> 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 <strong>the</strong> consequences <strong>of</strong> recruitment variationon <strong>the</strong> nature <strong>and</strong> intensity <strong>of</strong> species interactions in <strong>the</strong> adult habitat (e.g., Navarrete & Castilla1990, Moreno 1995, Navarrete et al. 2005, Wieters 2005); <strong>and</strong> (5) characterising <strong>the</strong> effects on <strong>the</strong>processes that regulate <strong>the</strong> dynamics <strong>of</strong> entire intertidal communities over large spatial scales(Navarrete et al. 2005).The far-reaching ramifications <strong>of</strong> persistent variation in recruitment have been most amplydemonstrated in recent studies that quantify patterns <strong>of</strong> recruitment over large temporal (years) <strong>and</strong>spatial (tens to hundreds <strong>of</strong> kilometres) scales. These studies are starting to shed light on, <strong>and</strong> findre<strong>current</strong> patterns in, <strong>the</strong> causes <strong>of</strong> <strong>the</strong> typically large, baffling <strong>and</strong> usually ‘unpredictable’ variationin coastal eco<strong>system</strong>s. Studies along <strong>the</strong> California coast have found large-scale regularities inpatterns <strong>of</strong> recruitment <strong>of</strong> sessile species that can help reconcile odd experimental results (Mengeet al. 1994, Connolly et al. 2001, Menge et al. 2003). Studies in <strong>the</strong> HCS conducted by Navarreteet al. (2002, 2005) have evaluated <strong>the</strong> effects <strong>of</strong> variation in wind-driven upwelling on communityregulation along 900 km <strong>of</strong> coastline between 29°S <strong>and</strong> 35°S during 72 months. Sharp discontinuitiesin upwelling regimes around 30–32°S produced abrupt <strong>and</strong> persistent breaks in <strong>the</strong> dynamics<strong>of</strong> benthic <strong>and</strong> pelagic communities over hundreds <strong>of</strong> kilometres (regional scales) (Figure 15A,B).Rates <strong>of</strong> mussel <strong>and</strong> barnacle recruitment changed sharply at 32°S, determining a geographic breakin adult abundance <strong>of</strong> <strong>the</strong>se competitively dominant species. Analyses <strong>of</strong> satellite images alsocorroborate <strong>the</strong> existence <strong>of</strong> regional-scale discontinuities in dynamics <strong>and</strong> concentration <strong>of</strong> <strong>of</strong>fshoresurface chl-a that had been previously described at coarser resolution (Thomas 1999, Thomas et al.2001b). Intertidal field experiments showed that <strong>the</strong> paradigm <strong>of</strong> top-down control <strong>of</strong> intertidalbenthic communities (Castilla & Durán 1985, Paine et al. 1985, Castilla 1999, Navarrete & Castilla2003) holds only south <strong>of</strong> this geographic discontinuity. To <strong>the</strong> north, populations seem recruitmentlimited, <strong>and</strong> predators have negligible effects, despite attaining similarly high abundances. Thus,geographically discontinuous oceanographic regimes set bounds to <strong>the</strong> strength <strong>of</strong> species interactions<strong>and</strong> define distinct regions for <strong>the</strong> design <strong>and</strong> implementation <strong>of</strong> sustainable management<strong>and</strong> conservation policies along <strong>the</strong> HCS. Fur<strong>the</strong>r ecological studies using molecular markers areneeded to define <strong>the</strong> consequences <strong>of</strong> this variation for <strong>the</strong> genetic population structure <strong>of</strong> mussels<strong>and</strong> barnacles, as well as for o<strong>the</strong>r components <strong>of</strong> intertidal communities, many <strong>of</strong> which do notexperience such a discontinuity in recruitment, despite having similar life histories <strong>and</strong> generalbiology (Figure 15C,D).250
THE HUMBOLDT CURRENT SYSTEM OF NORTHERN AND CENTRAL CHILE3.53.02.52.01.51.00.50.0A Chthamalid barnacles, high zone3.02.5B Perumytilus purpuratus, mid zoneRecruits day −1 collector −12.01.51.00.50.02.52.01.51.00.50.0706050403020100C Semimytilus algosus, mid zoneD Notobalanus flosculus, low zoneTEMNTEMARRGUAPTALMOLLMONCURQUNTUNELQTABOECIMNECIMSLCRUZCARTPELMAZPTLFigure 15 Average recruitment <strong>of</strong> intertidal invertebrates along <strong>the</strong> coast <strong>of</strong> <strong>central</strong> Chile at sites orderedfrom north to south, from ~29°S to 35°S. Data correspond to long-term (3–7 yr) averages per site <strong>of</strong> individualsfound in replicated collectors that replaced monthly. The arrow in panels (A) <strong>and</strong> (B) indicates approximateposition <strong>of</strong> regional discontinuity in intertidal chthamalid barnacles in <strong>the</strong> high intertidal zone <strong>and</strong> <strong>the</strong> dominantmussel Perumytilus purpuratus in <strong>the</strong> mid-zone. See Navarrete et al. (2005) for fur<strong>the</strong>r details.NDARRGUAPTALMOLLMONCURQUNTUNELQND NDTABOECIMNECIMSLCRUZCARTPELMAZPTLS251