MARTIN THIEL ET AL.Table 4 Different types <strong>of</strong> material transfer between communities within <strong>the</strong> HCS <strong>of</strong> nor<strong>the</strong>rnChile. Distances <strong>of</strong> transport increase with increasing length <strong>of</strong> line, intensity <strong>of</strong> transfer increaseswith increasing size, <strong>and</strong> frequency augments with increasing number <strong>of</strong> dots.Material type Agent Distance Intensity Frequency ReferenceBetween Realms TERRESTRIAL (T) –MARINE (M)Particulate inorganic matter River (T to M)(mining discharge)Dissolved metalsRiver (T to M)(mining discharge)Particulate inorganic matter River (T to M)(river floods)Organic matterCurrents(carcasses <strong>and</strong> algae)Organic matterTerrestrialvertebrates(M to T)Nutrients <strong>and</strong> dead biomass Seabirds(food)(M to T)● ●●●●● Lancellotti & Stotz 2004●●●●●●Vásquez et al. 1999Vásquez et al. 2000 ● Mir<strong>and</strong>a 2001●●●●●●●●●●●●●Guppy 1906Arntz & Fahrbach 1991Navarrete & Castilla 1993Fariña et al. 2003aSabat et al. 2003Sanchez-Pinero & Polis2000 Ludynia et al. 2005Between Environments PELAGIC-BENTHICPOM & phytoplankton Suspension feeders ● ●●● Uribe & Blanco 2001POM (algal detritus) CurrentsBustamante & Branch●●●●1996 Tala & Edding 2005Between Benthic Habitats NEIGHBOURING COMMUNITIESPOM (detached algae) CurrentsShell remainsWaves <strong>and</strong> <strong>current</strong>s●●●●●●●●●●●●Rodríguez 2003Tala & Edding 2005Bomkamp et al. 2004Personal observationsNote: POM = particulate organic matter.& Castro 2003). The transfer <strong>of</strong> large amounts <strong>of</strong> algal fragments from subtidal kelp forests toward<strong>the</strong> shore has been considered as a principal food source, structuring <strong>and</strong> maintaining macr<strong>of</strong>aunacommunities on s<strong>and</strong>y beaches (Colombini et al. 2000, Dugan et al. 2003). Transport <strong>of</strong> detachedkelp plants or parts to aggregations <strong>of</strong> sea urchins in tide pools is considered to be an importanttrophic subsidy for <strong>the</strong>se grazers (Rodríguez 2003). Arrival <strong>of</strong> kelp in <strong>the</strong> intertidal zone <strong>of</strong> nor<strong>the</strong>rn<strong>central</strong>Chile continues throughout <strong>the</strong> year, but highest quantities arrive from late spring until earlyautumn, also depending on <strong>the</strong> proximity to source habitats (Rodríguez 2003). The importance <strong>of</strong>kelp transfer to deeper subtidal habitats (for <strong>the</strong> Californian coast see, e.g., Kim 1992, Harroldet al. 1998, Vetter & Dayton 1998, 1999) or to <strong>the</strong> rocky subtidal zone has not been evaluated in<strong>the</strong> HCS, but given that <strong>the</strong> main kelp species are non-buoyant (Lessonia spp.), it is assumed thatlarge fractions <strong>of</strong> detached kelp may be accumulating on deeper or wave-sheltered subtidal bottoms.In addition to kelp detritus, hard-bottom communities also export large quantities <strong>of</strong> shellremains to NCs (Bomkamp et al. 2004). Along <strong>the</strong> coast <strong>of</strong> nor<strong>the</strong>rn-<strong>central</strong> Chile, shell gravel isrelatively common near exposed headl<strong>and</strong>s (Ramorino & Muñiz 1970). These sediments are mainlycomposed <strong>of</strong> shell fragments from barnacles, sea urchins <strong>and</strong> bivalves, but source habitats, fluxes<strong>of</strong> <strong>the</strong>se materials from hard bottoms to sediments <strong>and</strong> <strong>the</strong> relevance <strong>of</strong> local hydrography havenot been examined.246
THE HUMBOLDT CURRENT SYSTEM OF NORTHERN AND CENTRAL CHILEFrequency <strong>and</strong> intensity <strong>of</strong> exchange processesExchange <strong>of</strong> nutrients or particulate matter among marine communities in nor<strong>the</strong>rn-<strong>central</strong> Chilevaries in frequency <strong>and</strong> intensity (Table 4). Some <strong>of</strong> <strong>the</strong> most important <strong>and</strong> frequent exchangeprocesses in nor<strong>the</strong>rn Chile occur in <strong>the</strong> vertical direction (sedimentation <strong>of</strong> POM, release <strong>of</strong>nutrients into <strong>the</strong> water column, upwelling <strong>of</strong> nutrient-rich waters). Horizontal transfer processesappear to be most intense <strong>and</strong> frequent in coastal habitats, such as, for example, supply <strong>of</strong> kelpdetritus to NCs. In contrast to this relatively continuous exchange <strong>of</strong> material, depositions <strong>of</strong>terrestrial sediments to coastal waters or <strong>of</strong> dead plants <strong>and</strong> animals to local beaches appear to besome <strong>of</strong> <strong>the</strong> least frequent <strong>and</strong> unpredictable transfer events. When <strong>the</strong>se events occur, <strong>the</strong>ir intensityis <strong>of</strong>ten so high (e.g., Arntz 1986) that <strong>the</strong>y exceed <strong>the</strong> escape or ingestion capacity <strong>of</strong> <strong>the</strong> organismsin <strong>the</strong> receiving habitats. This can result in <strong>the</strong> destruction <strong>of</strong> local communities <strong>and</strong> <strong>the</strong> incorporation<strong>of</strong> materials to deeper sediment layers. Transfer <strong>of</strong> marine-derived materials in colonies <strong>of</strong>seabirds <strong>and</strong> sea lions is also very intense (<strong>and</strong> frequent), but in nor<strong>the</strong>rn-<strong>central</strong> Chile cannot beutilised by terrestrial organisms due to lack <strong>of</strong> water. A similar effect is observed in <strong>the</strong> watercolumn <strong>and</strong> sediments <strong>of</strong> <strong>the</strong> OMZ where recycling processes are suppressed due to <strong>the</strong> lack <strong>of</strong>oxygen (Graco et al. 2006). Thus <strong>the</strong> intensity <strong>of</strong> <strong>the</strong> fluxes, which overcome <strong>the</strong> recycling capacity<strong>of</strong> receiving communities, may favour <strong>the</strong> long-term storage <strong>of</strong> POM not only in shelf sediments(H.E. González et al. 2004a), but also in terrestrial, intertidal <strong>and</strong> subtidal habitats <strong>of</strong> <strong>the</strong> HCS(isl<strong>and</strong>s with seabird <strong>and</strong> sea lion colonies, s<strong>and</strong>y beaches, subtidal kelp accumulations). It appearsto be important to estimate carbon <strong>and</strong> nutrient export (<strong>and</strong> storage) not only to shelf sedimentsbut also to terrestrial soils <strong>and</strong> intertidal <strong>and</strong> subtidal bottoms along <strong>the</strong> HCS.Propagule supply, dispersal <strong>and</strong> recruitment variabilityExchange <strong>of</strong> biological information (i.e., gene flow) depends on <strong>the</strong> dispersal ability <strong>of</strong> <strong>the</strong> organismsin question. Dispersal <strong>of</strong> individuals determines <strong>the</strong> scale at which species interact with <strong>the</strong>physical environment, <strong>the</strong> nature <strong>and</strong> consequences <strong>of</strong> <strong>the</strong> interaction with o<strong>the</strong>r species, <strong>the</strong> wayin which <strong>the</strong>y respond to perturbations <strong>and</strong> ultimately <strong>the</strong> selective forces <strong>and</strong> rates to evolve,speciate or go extinct. Because in most benthic habitats <strong>the</strong>re is a predominance <strong>of</strong> species withcomplex life cycles, which include a free-swimming larval stage (Thorson 1950, Strathmann 1990),high dispersal capabilities are intuitively associated with most marine organisms. However, this isnot a rule since coexisting with species with planktonic larvae <strong>the</strong>re always exists a myriad <strong>of</strong>species with very limited dispersal potential, such as most macroalgae <strong>and</strong> direct developers orbrooding species (Reed et al. 1992, Kinlan & Gaines 2003, Shanks et al. 2003b). Moreover <strong>and</strong> t<strong>of</strong>ur<strong>the</strong>r complicate things, many species use rafting as an alternative method <strong>of</strong> long-distancedispersal (Santelices 1990a, Thiel & Gutow 2005). Despite <strong>the</strong> early realisation <strong>of</strong> <strong>the</strong> high diversity<strong>of</strong> life cycles found in every marine habitat, <strong>the</strong> ecological consequences <strong>of</strong> such diversity onspecies interactions <strong>and</strong> on <strong>the</strong> structure <strong>and</strong> dynamics <strong>of</strong> benthic communities are only beginningto be unveiled (Kinlan & Gaines 2003, Leibold et al. 2004, Velázquez et al. 2005).Methodological approaches to <strong>the</strong> study <strong>of</strong> dispersalThe study <strong>of</strong> dispersal in <strong>the</strong> ocean is fraught with methodological problems imposed by <strong>the</strong>difficulty <strong>of</strong> following <strong>the</strong> usually microscopic propagules over extended time. Indirect methods toestimate aspects <strong>of</strong> dispersal have been developed. For instance, <strong>the</strong> use <strong>of</strong> highly variable neutralDNA markers <strong>of</strong>fers an unprecedented opportunity to estimate realised dispersal distances (Palumbi247