MARTIN THIEL ET AL.28°S30°S 32°S 34°S 36°S0.15A0.10.0500.03B0.02Reproductive output0.0100.1250.020.0750.050.02500.50.4CD0.30.20.10Brood sizen/basal area500400300200100E0HuascoPta. ChorosTembladorCta. HornosArrayanTotoralilloGuanaquerosLos MollesMontemarQuintayEl QuiscoConsistorialMatanzaPi<strong>chile</strong>muFigure 19 Reproductive output <strong>of</strong> (A) Concholepas concholepas, (B) Acanthina monodon, (C) Chiton granosus,(D) Perumytilus purpuratus, <strong>and</strong> (E) brood size (number <strong>of</strong> embryos per unit <strong>of</strong> basal area) <strong>of</strong> Nothochthamalusscabrosus, along <strong>the</strong> study site which ranges from 28°S to 36°S in <strong>the</strong> eastern South Pacific Ocean. The whitebars are used for carnivore species, <strong>the</strong> black bars for herbivore or filter-feeding species. The white arrowsindicate upwelling centers, <strong>the</strong> black arrows point to sites not influenced by upwelling along <strong>the</strong> HCS.R = 0.64, N. scabrosus-Ch. granosus: R = 0.73; Fernández et al. 2007). Investment in gonads <strong>of</strong>carnivore species does not show any correlation with <strong>the</strong> reproductive patterns exhibited by herbivoresor suspension-feeding species. The patterns reported were consistent over <strong>the</strong> 3-yr study(coefficient <strong>of</strong> variation = 1.3%). These results suggest that <strong>the</strong> small-scale variation in environmentalconditions along <strong>the</strong> upwelling-favourable region <strong>of</strong> <strong>the</strong> HCS seems to affect gonad production<strong>and</strong> consequently larval production, <strong>and</strong> <strong>the</strong>refore that some locations potentially serve assource populations <strong>of</strong> propagules. Transplant experiments support <strong>the</strong> hypo<strong>the</strong>sis that local environmentalconditions determine reproductive output. Suspension feeders (e.g., Perumytilus purpuratus)266
THE HUMBOLDT CURRENT SYSTEM OF NORTHERN AND CENTRAL CHILE<strong>and</strong> herbivores (e.g., Chiton granosus) transplanted between <strong>the</strong> most <strong>and</strong> least suitable sites forreproduction in <strong>central</strong> Chile showed that reproductive output was strongly determined by <strong>the</strong> siteto which <strong>the</strong> animals were transplanted while <strong>the</strong> site <strong>of</strong> origin showed a negligible effect (Fernándezet al. 2007). Organisms transplanted to Los Molles showed high reproductive output <strong>and</strong> organismstransplanted to Matanzas showed low reproductive output, regardless <strong>of</strong> <strong>the</strong> site <strong>of</strong> origin (Fernándezet al. 2007). These contrasting results suggest that environmental variables, such as PP, may affectinvestment in gonads <strong>of</strong> lower trophic level benthic invertebrates. These environmental conditionsseem to be related to <strong>the</strong> spatial variation <strong>of</strong> upwelling conditions. The <strong>central</strong> coast <strong>of</strong> Chile isdominated by seasonal wind-driven upwelling that forces cold, nutrient-rich water into <strong>the</strong> upperwater column (Wieters et al. 2003). However, it is remarkable that <strong>the</strong> well-documented relationshipbetween cold upwelled water <strong>and</strong> high chl-a concentration over large spatial scales <strong>of</strong>f <strong>the</strong> coasts<strong>of</strong> Chile <strong>and</strong> California (Strub et al. 1991, Thomas et al. 2001a) is not observed at smaller spatialscales (Wieters et al. 2003). Between 28°S <strong>and</strong> 36°S, <strong>the</strong> lowest chl-a concentrations are associatedwith coldest upwelled waters (Wieters et al. 2003). Matanzas <strong>and</strong> Montemar are sites influencedby upwelling centres, in contrast with <strong>the</strong> lower influence <strong>of</strong> upwelling in areas such as Los Mollesor Consistorial (Broitman et al. 2001, Wieters et al. 2003). Upwelling centres also show highergrowth rate <strong>of</strong> corticated algae, which are not consumed by herbivores, <strong>and</strong> low growth <strong>of</strong> ephemeralalgae (Nielsen & Navarrete 2004). Although temperature decreased from 28°S to 36°S <strong>and</strong> is lowerin upwelling centres, gonad production is not correlated with seawater temperature (Fernándezet al. 2006a). Most likely, <strong>the</strong> low chl-a concentration associated with upwelling conditions (Wieterset al. 2003) <strong>and</strong> low abundance <strong>of</strong> benthic ephemeral algae (Nielsen & Navarrete 2004) are <strong>the</strong>main factors affecting reproductive output <strong>of</strong> lower trophic level, intertidal species along <strong>the</strong> HCS.Evidence from o<strong>the</strong>r geographic regions supports <strong>the</strong> hypo<strong>the</strong>sis that patterns <strong>of</strong> PP associated withupwelling conditions determine reproductive output (Leslie et al. 2005). However, more informationis necessary to clearly identify <strong>the</strong> set <strong>of</strong> environmental variables affecting reproductive investment.Temperature <strong>and</strong> brooding requirementsAlthough <strong>the</strong> effect <strong>of</strong> temperature on gonad production is not evident along <strong>the</strong> upwelling regionassociated with <strong>the</strong> HCS between 28°S <strong>and</strong> 36°S, studies conducted over larger spatial scales (<strong>and</strong>wider temperature ranges) suggest that temperature can affect egg production in species thataggregate embryos. Oxygen is a limiting factor in embryo aggregations <strong>of</strong> marine invertebrates(Cohen & Strathmann 1996, Lee & Strathmann 1998, Fernández et al. 2003) <strong>and</strong> temperatureaffects oxygen availability in different types <strong>of</strong> embryo packing (Brante et al. 2003, Fernándezet al. 2006a). Studies <strong>of</strong> <strong>the</strong> brachyuran crab Cancer setosus show that brooding females respondto <strong>the</strong> increased oxygen dem<strong>and</strong> <strong>of</strong> <strong>the</strong> embryos at higher temperatures by increasing abdominalflapping frequency, a behaviour that supplies oxygen to <strong>the</strong> brood (Brante et al. 2003). Similarpatterns <strong>of</strong> female response to embryo oxygen dem<strong>and</strong> have been reported throughout embryodevelopment in o<strong>the</strong>r crab species (Baeza & Fernández 2002, M. Fernández et al. 2002). The changein female brooding behaviour (abdominal flapping frequency) produces a higher rate <strong>of</strong> oxygensupply, dramatically affecting <strong>the</strong> costs <strong>of</strong> brooding. Between 10°C <strong>and</strong> 18°C, a 45% increase inbrooding costs was estimated for large-size crabs, such as C. setosus (Brante et al. 2003). Thissubstantial increase in brooding behaviour <strong>and</strong> cost seems to affect egg production <strong>and</strong> survival(Fernández et al. 2003). Field data showed that gonad investment (or reproductive output) inC. setosus is lower in nor<strong>the</strong>rn Chile (approximately 20°S) than in <strong>central</strong> (30–33°S) <strong>and</strong> sou<strong>the</strong>rn(40°S) Chile. Lardies & Castilla (2001) reported a similar latitudinal trend in reproductive outputfor Pinnaxodes <strong>chile</strong>nsis. Moreover, embryo loss in Cancer setosus increases with temperature(Brante et al. 2003), suggesting that temperature also affects embryo survival throughout <strong>the</strong>brooding period. Reproductive output <strong>of</strong> most brachyuran crab species does not vary south <strong>of</strong> 30°S267
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