the humboldt current system of northern and central chile - figema

THE HUMBOLDT CURRENT SYSTEM OF NORTHERN AND CENTRAL CHILEand herbivores (e.g., Chiton granosus) transplanted between the most and least suitable sites forreproduction in central Chile showed that reproductive output was strongly determined by the siteto which the animals were transplanted while the site of origin showed a negligible effect (Fernándezet al. 2007). Organisms transplanted to Los Molles showed high reproductive output and organismstransplanted to Matanzas showed low reproductive output, regardless of the site of origin (Fernándezet al. 2007). These contrasting results suggest that environmental variables, such as PP, may affectinvestment in gonads of lower trophic level benthic invertebrates. These environmental conditionsseem to be related to the spatial variation of upwelling conditions. The central coast of Chile isdominated by seasonal wind-driven upwelling that forces cold, nutrient-rich water into the upperwater column (Wieters et al. 2003). However, it is remarkable that the well-documented relationshipbetween cold upwelled water and high chl-a concentration over large spatial scales off the coastsof Chile and California (Strub et al. 1991, Thomas et al. 2001a) is not observed at smaller spatialscales (Wieters et al. 2003). Between 28°S and 36°S, the lowest chl-a concentrations are associatedwith coldest upwelled waters (Wieters et al. 2003). Matanzas and Montemar are sites influencedby upwelling centres, in contrast with the lower influence of upwelling in areas such as Los Mollesor Consistorial (Broitman et al. 2001, Wieters et al. 2003). Upwelling centres also show highergrowth rate of corticated algae, which are not consumed by herbivores, and low growth of ephemeralalgae (Nielsen & Navarrete 2004). Although temperature decreased from 28°S to 36°S and is lowerin upwelling centres, gonad production is not correlated with seawater temperature (Fernándezet al. 2006a). Most likely, the low chl-a concentration associated with upwelling conditions (Wieterset al. 2003) and low abundance of benthic ephemeral algae (Nielsen & Navarrete 2004) are themain factors affecting reproductive output of lower trophic level, intertidal species along the HCS.Evidence from other geographic regions supports the hypothesis that patterns of PP associated withupwelling conditions determine reproductive output (Leslie et al. 2005). However, more informationis necessary to clearly identify the set of environmental variables affecting reproductive investment.Temperature and brooding requirementsAlthough the effect of temperature on gonad production is not evident along the upwelling regionassociated with the HCS between 28°S and 36°S, studies conducted over larger spatial scales (andwider temperature ranges) suggest that temperature can affect egg production in species thataggregate embryos. Oxygen is a limiting factor in embryo aggregations of marine invertebrates(Cohen & Strathmann 1996, Lee & Strathmann 1998, Fernández et al. 2003) and temperatureaffects oxygen availability in different types of embryo packing (Brante et al. 2003, Fernándezet al. 2006a). Studies of the brachyuran crab Cancer setosus show that brooding females respondto the increased oxygen demand of the embryos at higher temperatures by increasing abdominalflapping frequency, a behaviour that supplies oxygen to the brood (Brante et al. 2003). Similarpatterns of female response to embryo oxygen demand have been reported throughout embryodevelopment in other crab species (Baeza & Fernández 2002, M. Fernández et al. 2002). The changein female brooding behaviour (abdominal flapping frequency) produces a higher rate of oxygensupply, dramatically affecting the costs of brooding. Between 10°C and 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 and cost seems to affect egg production and survival(Fernández et al. 2003). Field data showed that gonad investment (or reproductive output) inC. setosus is lower in northern Chile (approximately 20°S) than in central (30–33°S) and southern(40°S) Chile. Lardies & Castilla (2001) reported a similar latitudinal trend in reproductive outputfor Pinnaxodes chilensis. Moreover, embryo loss in Cancer setosus increases with temperature(Brante et al. 2003), suggesting that temperature also affects embryo survival throughout thebrooding period. Reproductive output of most brachyuran crab species does not vary south of 30°S267