the humboldt current system of northern and central chile - figema

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MARTIN THIEL ET AL.PERUIquique−20°Antofagasta−25°−30°Coquimbo−30°Southern latitude−33°CHILE−35°Concepción−40°1 2 3 4 5 6 7 8 9 10111213 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30Figure 17 Break points of distribution along the north-central Chilean coast documented in 29 biogeographicalclassifications published between 1951 and 2006 (breaks outside the range 17–38°S are not shown). Thefigure includes a wide spectrum of animal and macroalgal taxa of varying hierarchical levels, life forms andhabitats, and some classifications may partially overlap in one or more of these categories. Each classificationis represented along an imaginary vertical axis in correspondence with the numbers at the bottom, wheredashed lines denote the zones in which break points were found (each one marked by a thick horizontal dash),ranging from one to three break points per study. Horizontal lines highlight the latitudes 30°S and 33°S wherebreak points tend to concentrate. Classifications (for numbers 1–10 and 11–22, see references in compilationsby Brattström & Johanssen 1983 and Camus 2001, respectively): 1, Mollusca (Carcelles & Williamson 1951);2, Foraminifera (Boltovskoy 1964); 3, Mollusca (Marincovich 1973); 4, several animal taxa (Knox 1960);5, eulittoral organisms (Hartmann-Schröder & Hartmann 1962); 6, intertidal Mollusca (Dell 1971); 7, benthicanimals (Semenov 1977); 8, several animal taxa (Viviani 1979); 9, Anthozoa (Sebens & Paine 1979); 10,several animal taxa (Brattström & Johanssen 1983); 11, benthic macroalgae (Santelices 1980); 12, Bryozoa(Moyano 1991); 13, fishes (Mann 1954); 14, Isopoda (Menzies 1962); 15, several animal taxa (Ekman 1953);16, several animal taxa (Balech 1954); 17, planktonic Euphausiids (Antezana 1981); 18, Asteroidea (Madsen1956); 19, macroalgae (Alveal et al. 1973); 20, sandy beach Isopoda (Jaramillo 1982); 21, Porifera Demospongiae(Desqueyroux & Moyano 1987); 22, several invertebrate taxa (Lancellotti & Vásquez 1999); 23,demersal fishes (Sielfeld & Vargas 1996); 24, littoral Teleostei (Ojeda et al. 2000); 25, Phaeophyta (Meneses& Santelices 2000); 26, Rhodophyta (Meneses & Santelices 2000); 27, several animal and algal taxa (Camus2001); 28, Peracarid crustaceans (Thiel 2002); 29, benthic Polychaeta (Hernández et al. 2005); 30, pelagicbarnacles (Hinojosa et al. 2006).variations of mollusc diversity along the HCS, which would be determined by shelf area (Valdovinoset al. 2003), while the distribution of some littoral species appears more related to regional variationsin temperature trends (Rivadeneira & Fernández 2005). Thus, the transitions in northern Chile are256
THE HUMBOLDT CURRENT SYSTEM OF NORTHERN AND CENTRAL CHILEnot readily explained simply by the contact between warm and cold biotas, and proper explanationswill require a multivariate, integrative approach and an exploration of possible external forcings.The role of past and present processes in northern-central Chile (18–35°S)Different lines of historical and ecological evidence suggest that northern-central Chile constitutesa very complex and dynamical biogeographic scenario. Clearly, present-day patterns are notdivorced from physical changes related to the origin and installation of the cold HCS during theTertiary or from subsequent Quaternary fluctuations (e.g., see Villagrán 1995, Hinojosa & Villagrán1997, Villa-Martínez & Villagrán 1997, Maldonado & Villagrán 2002). The establishment of theHCS had involved both the northward advance of the subantarctic biota and the northward retractionof a former tropical/subtropical biota (Brattström & Johanssen 1983, Camus 2001), with consequencesthat may persist until the present, reflected in the heterogeneous character of the northernbiota. For instance, 10 of the nowadays most common bivalves in northern Chile exhibit upperthermal tolerances exceeding the highest temperatures recorded during EN events in the past century(Urban 1994), which is unexpected for species evolving in a cold upwelling system. At least oneof them (Argopecten purpuratus) is thought to be a relict of the Miocene tropical/subtropical fauna(Wolff 1987). Such physiological ‘anomalies’ suggest the presence of an inertial faunistic componentwithin the modern northern biota (i.e., remnants of the former warm fauna that escaped the forcedretraction to lower latitudes, and maintained their warm-water characteristics facilitated by recurrentpost-Miocene warming events such as EN) (Wolff 1987). In comparison, the marine flora appearsmore homogeneous and dominated mainly by subantarctic species, while tropical/subtropical speciesare virtually absent (Santelices & Meneses 2000). For instance, some common and ecologicallyimportant kelp species are not only more sensitive to warming episodes but also their upper thermaltolerance varies in accordance with the thermal latitudinal gradient (Martínez 1999).In this regard, the northern fauna underwent repeated distributional alterations in the pastassociated with climatic fluctuations. Some of them involved the simultaneous range retraction andexpansion of different species (e.g., Ortlieb et al. 1994), but more often the occurrence of tropical/subtropical fauna related to warming (EN-like) events in the Pleistocene (e.g., Ortlieb 1995) andHolocene (e.g., Llagostera 1979). Moreover, Neogene processes related to the establishment of themodern upwelling system in the HCS (e.g., shallowing of the OMZ) provoked a mass extinctionof bivalve molluscs (>75% of species), with lasting impacts on their current distribution patternsand biological characteristics (Rivadeneira 2005), and similar effects have been suggested for thepolychaete fauna (R.A. Moreno et al. 2006a). Notwithstanding, the causal relationships betweenhistorical events and current distribution patterns in northern Chilean waters remain largely unexplored,although their importance may be overwhelming.On the other hand, modern processes also have strong influences in northern Chile, particularlyinterannual fluctuations related to ENSO, which, however, should be looked at retrospectively,acknowledging the frequency and importance of EN-like events throughout the Holocene (e.g, seeMaldonado & Villagrán 2002). Strong EN events can modify the taxonomic composition of littoralcommunities (e.g., Arntz 1986, Castilla & Camus 1992, Camus et al. 1994, Vega et al. 2005,Vásquez et al. 2006) and the geographical occurrence of many species including key structuralcomponents such as intertidal and subtidal kelps (e.g., Lessonia nigrescens, L. trabeculata andMacrocystis pyrifera). Short-term modifications of community composition during EN occurthrough local extinctions and invasions, depending also on local conditions, which either favour orprevent their occurrence (Arntz 1986, Camus et al. 1994, Martínez et al. 2003, Castilla et al. 2005a).Moreover, the impacts on key species may scale up to produce long-term biogeographic changes,as exemplified by the dramatic effects of the 1982–1983 EN event on the intertidal kelp Lessonia257
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