the humboldt current system of northern and central chile - figema

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MARTIN THIEL ET AL.speak of a ‘transitory fauna’ in biotic substrata (see also Vásquez & Santelices 1984, Cerda &Castilla 2001). EEs may thus favour many mobile organisms that temporarily find shelter in thesehabitats (e.g., Vásquez et al. 2001b). In this context, Castilla et al. (2004b) reported that the intertidalascidian Pyura praeputialis facilitates the extension of mobile macrofauna from the subtidal intothe mid-intertidal zone, thereby enhancing local species richness.The main functional groups of the organisms associated with biotic habitats are suspensionfeeders (32.4% of all species), grazers (25.2%) and predators (23.4%) (H. Bastias & M. Thielunpublished data). Vásquez et al. (2001b) found very similar proportions of functional groups bothin kelp holdfasts and on the surrounding hard bottoms. By offering structural protection, EEs areconsidered to mediate species interactions and buffer the effect of physical stress, often favouringsuspension feeders (Wieters 2005, Valdivia & Thiel 2006). While the role of EEs in sustaining andpromoting local biodiversity on intertidal and subtidal hard bottoms has been elucidated in numerousstudies during the past decades (Vásquez & Santelices 1984, Villouta & Santelices 1984, Cerda &Castilla 2001, Sepúlveda et al. 2003a,b, Castilla et al. 2004b, Prado & Castilla 2006), relativelylittle is known about their trophic role on exposed rocky shores of northern-central Chile. Severalstudies have underlined the role of kelp forests as contributors of algal biomass to neighbouringhabitats (Rodríguez 2003) and as feeding grounds for fish predators that consume understory algaeand kelps (Angel & Ojeda 2001) or associated fauna (Núñez & Vásquez 1987, Palma & Ojeda2002). Fish consumers are known to play an important role in kelp food webs of northern-centralChile (Angel & Ojeda 2001, Fariña et al. in press) but little is known about the food webs in otherEEs. While most studies acknowledge the importance of EEs as habitat for associated organisms,their trophic efficiency (uptake of nutrients and suspended matter, release of dissolved and particulateorganic matter) and the role of associated macrofauna in the tropho-dynamics of communitieson intertidal and subtidal hard bottoms have not been thoroughly studied (see also Graham et al.2007). The high biomass and diverse assemblage of associated consumers suggest that EEs areenergetic power plants that concentrate and convert food resources in a similar way to kelp, seagrassor suspension feeder reefs in other parts of the world (e.g., Asmus & Asmus 1991, Lemmens et al.1996, Wild et al. 2004).Kelp forestsGiant kelp dominate shallow, subtidal rocky-bottom areas in temperate and cold seas down to adepth of ~40 m (Dayton et al. 1984, Harrold & Pearse 1987, Vásquez 1992, Graham et al. 2007).Kelp distribution from south Peru to central Chile is as follows: (1) intertidal rocky areas aredominated by Lessonia nigrescens, which forms belts along exposed coasts; (2) rocky subtidalenvironments are dominated by Lessonia trabeculata until 40 m in depth; (3) Macrocystis integrifoliaforms shallow kelp beds from the intertidal zone to depths of about 15 m. In southern-centralChile, these species are gradually replaced by Durvillaea antarctica, which dominates the intertidalzone in wave-exposed areas (Hoffmann & Santelices 1997), and in subtidal areas by Macrocystispyrifera, which occurs in both wave-exposed and –protected habitats (Buschmann et al. 2006a).While the two species from the genus Lessonia have an almost-continuous distribution along theentire Chilean continental coast, Macrocystis integrifolia has a fragmented distribution, formingpatchy populations in northern Chile. In this zone Lessonia trabeculata and Macrocystis integrifoliacoexist, but mixed kelp populations have segregated patterns of bathymetric distribution, M. integrifoliabeing more abundant in shallow areas (Vega et al. 2005). Local populations may vary fromhundreds of metres to hundreds of kilometres in extent. The observed distribution patterns are theresult of complex life-history strategies that interact with environmental factors such as spatial andtemporal variation in water movement, nutrient availability and temperature (Buschmann et al.2004b, V. Muñoz et al. 2004, Vega et al. 2005).240
THE HUMBOLDT CURRENT SYSTEM OF NORTHERN AND CENTRAL CHILEThe kelp forest communityKelp communities are highly productive (Dayton 1985), and they harbour a high diversity andabundance of invertebrates and fishes. Kelps, especially their holdfasts, constitute feeding areas,refuges against predation and bottom currents, spawning, settlement areas and nursery sites(Vásquez & Santelices 1984, Vásquez et al. 2001c, Vásquez & Vega 2005). Below the kelp canopya wide diversity of turf algae exists, including several Corallinales, Asparagopsis armata, Halopterispaniculata and Gelidium spp.; several species of barnacles and other sessile invertebrates (Pyurachilensis, Phragmatopoma moerchi, Aulacomya ater) are also part of the associated species shelteredby the kelp canopy (Vásquez et al. 2001b,c, Vásquez & Vega 2004a). In contrast to theNorthern Hemisphere, no large predators have been reported for southeastern Pacific kelp beds(Graham et al. 2007). Instead, invertebrate predators such as the muricid snail Concholepas concholepas,seastars (Meyenaster gelatinosus, Stichaster striatus, Heliaster helianthus and Luidiamagellanica), and intermediate-size coastal fishes (Cheilodactylus variegatus, Semicossyphus maculatusand Pinguipes chilensis) dominate the predator guild in kelp forests from northern-centralChile (Vásquez 1993b, Vásquez et al. 1998, 2006). These predators feed on a diverse guild ofherbivores, including sea urchins (Tetrapygus niger and Loxechinus albus), gastropods (Tegula spp.and Fissurella spp.), as well as fishes (Aplodactylus punctatus, Girella laevifrons and Kyphosusanalogus) (e.g., Medina et al. 2004). These herbivore species graze on kelp and associated algae,regulating their abundance and distribution (Vásquez & Buschmann 1997, Vega et al. 2005, Vásquezet al. 2006). Marine mammals widely distributed in the coastal zone of the HCS, such as sea lionsOtaria flavescens and sea otters Lontra felina, also use kelp beds as feeding areas.Population dynamics and spatial distribution of kelps in northern-central ChileThe kelp species from northern and central Chile belong to the Laminariales, which have a complexlife cycle with two morphologically different stages: one conspicuous stage, recognisable as kelpthat produces spores (the sporophytes), and a microscopic stage comprising independent femaleand male plants (the gametophytes) that lead a hidden life in the benthos. Sporophytes are theproduct of gametic reproduction, which is triggered by environmental factors (temperature, irradiance,photoperiod, and nutrient concentrations).The sporophytes themselves are reproductive year-round, but peak spore release has beenobserved during winter. Since spore survival in Laminariales is short, the dispersal range of kelpsis generally assumed to be quite reduced (Graham et al. 2007); if spores do not settle within arelatively short period they die (Santelices 1990a). However, spores may survive in the guts ofdifferent herbivores (Santelices & Correa 1985, Santelices & Payá 1989) or as filaments in darkness(Santelices et al. 2002). Furthermore, fertile floating plants may act as spore carriers and therebycontribute to dispersal (Macaya et al. 2005).Juvenile sporophytes of Lessonia recruit onto hard-bottom substrata during late winter–spring,and in the field are capable of producing spores after 6–8 months (Santelices & Ojeda 1984; seereview by Edding et al. 1994). Interference by adult plants inhibits the intertidal recruitment ofjuvenile L. nigrescens in exposed habitats. Nevertheless, water movements produce whiplash effects(sensu Dayton et al. 1984) that gives protection against grazers, thereby promoting successfulrecruitment of sporophytes (Santelices & Ojeda 1984). In subtidal habitats abundance of grazers,currents and reproductive behaviour of two species of elasmobranchs (Schroederichthys chilensisand Psammobatis scobina) affect Lessonia trabeculata populations. Grazing modifies algal morphology,producing two morphotypes: shrub-like and tree-like morphs. Water movement affectsthese differentially and generates higher mortality on tree-like morphs (Vásquez 1992). Shortdistances between plants (or high densities) reduce the access of grazers to the holdfasts. The241
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the humboldt current system of northern and central chile - figema

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