the humboldt current system of northern and central chile - figema

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MARTIN THIEL ET AL.Table 5 Thermal tolerance limits (LT 50 ), and spring maximal habitat temperature ofPetrolisthes along intertidal vertical gradient in a locality at the HCS (33°S)Species of PetrolisthesVertical positionin the intertidal~ Limit of thermal tolerance(LT 50 , °C)~ Maximal habitat temperature(°C)P. tuberculosus Low 27.5 14P. tuberculatus Mid-low 28.5 18P. violaceus Middle 30.5 18P. laevigatus Mid-high 31.5 28P. granulosus High 35.0 33Note: Data from Stillman & Somero (2000).habitat), which suggests the beginning of the organism’s decompensation, or the commencementof another homeostatic mechanism independent of oxygen consumption (Yaikin et al. 2002). Higherthermal stress or having thermal limits close to actual maximal habitat temperatures might increasethe ‘cost of living’ of the species in the upper intertidal (Somero 2002, Stillman 2002). This highercost of living would be associated with the cost of repairing thermal damage (heat-shock proteins,Hsp) and adapting systems through acclimatisation (Somero 2002). Although tropical Petrolisthesspecies have higher thermal limits than HCS species, the latter show a wider range of thermaltolerance between low and high intertidal species (Stillman & Somero 2000). Moreover, low intertidalHCS species show greater phenotypic plasticity in their thermal tolerance than high intertidal species(Stillman & Somero 2000). Considering global warming, species inhabiting the upper intertidalzone, living at the ‘edge’ of their thermal limits, would be more affected than species from thelower intertidal, which live far from their thermal limit and with a greater thermal phenotypicplasticity. These physiological traits may have an important effect on the borders in the latitudinaldistribution of a species and consequently also on biogeographic limits.Thermal effects that occur outside the normal physiological range involve deleterious changesat the cellular level, especially in systems involved with oxygen uptake, delivery and utilisation(Stillman 2002), such as the cardiac system (Frederich & Pörtner 2000). The heart of a crab speciesliving in the upper intertidal has an Arrhenius break temperature (ABT, temperature at which a breakoccurs in the slope in an Arrhenius plot, i.e., log rate vs. reciprocal of absolute temperature, K)that is 5°C higher than in a crab species from the low intertidal (Stillman & Somero 1996). Thesedifferences were associated with the Na + K + ATPase (adenosine triphosphatase) activity, which isnecessary for the establishment of the membrane action potential that permits the heartbeat (Stillman2002). Similar to the rate of heartbeat, oxygen consumption by isolated mitochondria exhibits a‘break’ at some high temperatures (Dahlhoff & Somero 1993). Phenotypic plasticity in the ABTof mitochondrial respiration has been observed in abalone Haliotis congeners from different thermalhabitats (latitude and vertical positions along subtidal-to-intertidal gradient) (Dahlhoff & Somero1993). Protein synthesis and heat-shock response has been shown to change spatially amonggastropod (Tegula) congeners from the temperate subtidal to the low intertidal zones (Tomanek2001) and seasonally in the bivalve Mytilus trossulus (Hofmann & Somero 1995). Hsp have thefunction of refolding and ‘rescuing’ proteins damaged by thermal denaturation (Becker & Craig1994, Hofmann & Somero 1995). Intertidal species of Tegula showed greater expression of Hsp70than the subtidal species when temperature increases (Tomanek 2001). The energy cost associatedwith replacing damaged proteins and maintaining Hsp may be an important proportion of cellularenergy demands (Hofmann & Somero 1995, Somero 2002).Intertidal and shallow subtidal invertebrates present a ‘cascade’ of physiological responses thatenable them to adapt and finally survive changes in environmental conditions. Despite the important264
THE HUMBOLDT CURRENT SYSTEM OF NORTHERN AND CENTRAL CHILElatitudinal and vertical environmental conditions gradient of the HCS, there are few studies ofphysiological responses of invertebrates living in this ecosystem. The range of temperatures registeredin the intertidal (rocky pools) along this latitudinal gradient (Pulgar et al. 2006) is very similarto the TGR from the low-to-high intertidal zone observed in central Chile (Table 5). Therefore, itcould be expected to find similar thermal physiological variability and local adaptations of congenersor conspecifics in the latitudinal gradient to those found in the intertidal vertical gradient.Because in this area the pattern of environmental variability shifts from a relatively predictableseasonal pattern to a more unpredictable pattern of high interannual variability (i.e., ENSO),physiological characterisation of congeners or conspecific organisms inhabiting the intertidal andshallow subtidal zones along the latitudinal gradient of the HCS would be particularly interesting.Moreover, since algal availability increases from northern to southern Chile (Santelices & Marquet1998), and physiological compensation associated with environmental stress increases cost of living(Somero 2002, Stillman 2002), latitudinal changes in food availability should also be consideredin future studies. It appears particularly interesting to examine how increased costs of living nearthe distribution limit of a species influences its reproductive potential.Reproductive patterns of selected marine invertebratesin the HCSSome of the factors that vary with upwelling intensity and persistence, such as temperature andPP, are known to critically affect per capita reproductive investment of marine invertebrates (e.g.,MacDonald & Thompson 1985, 1988, Clarke 1987, Brey 1995, Phillips 2002). In the northeasternPacific, reproductive hot spots coincide with regions exhibiting high PP, which suggests not onlythat bottom-up processes play a central role in explaining reproductive output, but also that spatialheterogeneity in reproduction needs to be considered in conservation and management plans (Leslieet al. 2005). The clear break in eddy kinetic energy and equatorward wind stress reported at 30°Sin the southeastern Pacific (Hormazábal et al. 2004) coincides with two contrasting regimes in chl-aconcentration both in coastal areas and offshore (Yuras et al. 2005). Chl-a concentration is negativelycorrelated with seawater temperature along the HCS (Strub et al. 1991, Thomas et al. 2001b).The effects of small- and large-scale variation in environmental conditions related to upwellingpersistence and strength on reproductive patterns along the HCS have recently been analysed.Primary productivity and gonad productionGonad and egg production of marine invertebrates do not exhibit a clear latitudinal cline in investmentin reproduction along the HCS in central Chile (Fernández et al. 2007). However, gonad productionshows variable patterns throughout the study region, which extends from 28°S to 36°S, and thisvariability appears related to the trophic level of the species being investigated and the proximity ofthe study sites to upwelling centres. Carnivores such as Concholepas concholepas and Acanthinamonodon do not show variation in gonad investment between 28°S and 36°S (Figure 19). In contrast,some of the dominant intertidal suspension-feeding species, Perumytilus purpuratus and Nothochthamalusscabrosus, and one of the most abundant herbivores, Chiton granosus, exhibit strongvariation in gonad production among sites, even between adjacent locations (Fernández et al. 2007).Investment in reproduction of suspension-feeding and herbivore species is constantly higher insome sites (e.g., Los Molles 32°24′S, Consistorial 33°49′S) and lower in others (e.g., Montemar32°96′S, Matanzas 33°96′S). Furthermore, there is a positive and significant correlation betweeninvestment in gonads among Perumytilus purpuratus, Nothochthamalus scabrosus and Chitongranosus (p always < 0.05; P. purpuratus-N. scabrosus: R = 0.89, P. purpuratus-Ch. granosus:265
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