MARTIN THIEL ET AL.species, <strong>the</strong>ir spatial <strong>and</strong> geographic extent, <strong>the</strong>ir temporal dynamics <strong>and</strong> <strong>the</strong>ir role as eco<strong>system</strong>engineers (EEs) will be described. Fur<strong>the</strong>r, it will be briefly discussed how <strong>the</strong> spatiotemporaldistribution <strong>of</strong> <strong>the</strong>se EEs may influence local biodiversity, population dynamics <strong>and</strong> trophic interactionsin hard-bottom communities along <strong>the</strong> HCS.Habitat-forming species on hard bottomsLarge kelps (Lessonia nigrescens, L. trabeculata, Macrocystis integrifolia, M. pyrifera <strong>and</strong> Durvillaeaantarctica), which grow abundantly in <strong>the</strong> low intertidal <strong>and</strong> shallow subtidal zone <strong>of</strong> <strong>the</strong> HCS,have compact <strong>and</strong> complex holdfasts that <strong>of</strong>fer abundant <strong>and</strong> diverse microhabitats on <strong>the</strong> rocksubstratum itself. Their stipes <strong>and</strong> blades reach lengths <strong>of</strong> 2.5 m (Lessonia trabeculata) up to 30 m(Macrocystis pyrifera), <strong>and</strong> <strong>the</strong>y have an important effect on local hydrodynamics because <strong>the</strong>y actas wave breakers <strong>and</strong> slow down <strong>current</strong>s (Graham 2004). Smaller macroalgae with shor<strong>the</strong>r thalli<strong>of</strong> 5–50 cm (such as Halopteris funicularis, Glossophora kunthii, Asparagopsis armata, Corallina<strong>of</strong>ficinalis <strong>and</strong> Gelidium <strong>chile</strong>nse) form dense carpets (turfs) that <strong>of</strong>fer primary <strong>and</strong> secondarymicrohabitats because <strong>the</strong>y act as sediment traps retaining s<strong>and</strong> <strong>and</strong> shell fragments between <strong>the</strong>irthalli <strong>and</strong> stolons (López & Stotz 1997, Kelaher & Castilla 2005).A diverse group <strong>of</strong> suspension-feeding EEs on hard bottoms include polychaetes (Phragmatopomamoerchi), barnacles (Austromegabalanus psittacus), bivalves (Perumytilus purpuratus, Semimytilusalgosus, Choromytilus chorus <strong>and</strong> Aulacomya ater), <strong>and</strong> ascidians (Pyura <strong>chile</strong>nsis <strong>and</strong>P. praeputialis). Their matrices reach heights <strong>of</strong> 2–40 cm, <strong>of</strong>fering abundant space between livingindividuals (Cerda & Castilla 2001) or in remaining tubes or shells <strong>of</strong> dead individuals. Matrices<strong>of</strong> <strong>the</strong>se suspension feeders may also retain considerable amounts <strong>of</strong> sediments (Prado & Castilla2006), <strong>the</strong>reby providing secondary substratum for associated organisms.Habitat-forming species compete among <strong>the</strong>mselves for space on hard-bottom substrata. Severalstudies indicate that mussels are competitively superior over barnacles (Navarrete & Castilla 1990,2003, Tokeshi & Romero 1995a) <strong>and</strong> can also overgrow turf algae (Wieters 2005), ascidians mayoutcompete mussels (Castilla et al. 2004a) or barnacles (Valdivia et al. 2005), <strong>and</strong> large kelp mayrecruit in <strong>and</strong> <strong>the</strong>n overgrow turf algae (Camus 1994a). Superior competitors <strong>the</strong>mselves may besuppressed by predators (e.g., mussels <strong>and</strong> ascidians by gastropod <strong>and</strong> seastar predators; Paine et al.1985, Castilla 1999, Castilla et al. 2004b) <strong>and</strong> grazers (Vásquez & Buschmann 1997, Buschmannet al. 2004a). Humans, acting as top predators by removing intermediate consumers, also stronglyinfluence <strong>the</strong> structure <strong>of</strong> hard-bottom communities in nor<strong>the</strong>rn <strong>and</strong> <strong>central</strong> Chile (Moreno et al.1986, Castilla 1999). Fur<strong>the</strong>rmore, recruitment <strong>and</strong> growth <strong>of</strong> habitat-forming species are controlledby a variety <strong>of</strong> processes (e.g., upwelling) that drive larval <strong>and</strong> food supply (Navarrete et al. 2002,Nielsen & Navarrete 2004, Wieters 2005). Following disturbances <strong>and</strong> detachment, open space onhard bottoms is quickly recolonised, starting with ephemeral algae, which subsequently are replacedby large <strong>and</strong> long-lived turf or kelp algae <strong>and</strong> suspension feeders (Durán & Castilla 1989; Valdiviaet al. 2005).Spatial <strong>and</strong> temporal dynamics <strong>of</strong> eco<strong>system</strong> engineersThe geographic range <strong>of</strong> most macroalgae <strong>and</strong> suspension-feeding EEs extends throughout nor<strong>the</strong>rn<strong>central</strong>Chile (into Peru), but not all <strong>of</strong> <strong>the</strong>m have a continuous latitudinal distribution (Table 3).All EEs from hard bottoms have pelagic dispersal stages, but in <strong>the</strong> case <strong>of</strong> <strong>the</strong> macroalgae <strong>the</strong>planktonic phase is <strong>of</strong> short duration (minutes to hours).Kelps <strong>of</strong> <strong>the</strong> genera Lessonia <strong>and</strong> Macrocystis extend from sou<strong>the</strong>rn Chile to north <strong>of</strong> 18°S,but EN events may provoke large-scale extinctions in nor<strong>the</strong>rn Chile (see also Kelp forests,236
THE HUMBOLDT CURRENT SYSTEM OF NORTHERN AND CENTRAL CHILETable 3 Main eco<strong>system</strong> engineer species from intertidal <strong>and</strong> subtidal hard bottoms along <strong>the</strong> Humboldt Current System <strong>of</strong> nor<strong>the</strong>rn <strong>and</strong> <strong>central</strong>ChileEco<strong>system</strong> engineerZonation(m)Waveexp.Height <strong>of</strong>patches (m) Size <strong>of</strong> patches (m 2 ) Latitudinal extent (°)Distance betweenpatches (km)Patch persistence(years)< 11 to 1010 to 1000> 100018,1920,2122,2324,2526,2728,2930,3132,3334,3536,3738,39< 11 to 1010 to 1000> 1000< 11 to 10>10Lessonia trabeculata 0–30 E,S,P 2.5 x x x x x xLessonia nigrescens 0 E,S 6 x x x x x xMacrocystis integrifolia 0–15 S,P 10 x x x x x xMacrocystis pyrifera 0–30 S,P 30 x x x x xDurvillaea antarctica 0 E 15 x x x x x xGlossophora kunthii 0–8 E,S,P 0.25 x x x x x xHalopteris funicularis 0–8 E,S,P 0.1 x x x x x xAsparagopsis armata 0–8 S,P 0.12 x x x x x xCorallina <strong>of</strong>ficinalis 0–8 E,S,P 0.15 x x x x x xGelidium <strong>chile</strong>nse 0–2 E,S,P 0.06 x x x x xPhragmatopoma moerchi 0 E 0.2 x x x xPerumytilus purpuratus 0 E 0.05 x x x x x x x xSemimytilus algosus 0 E 0.1 x x x x x xAulacomya ater 10–20 E 0.2 x x x x x x xAustromegabalanus psittacus 0–20 E,S 0.2 x x x x xPyura <strong>chile</strong>nsis 1–20 E,S,P 0.2 x x x x x xPyura praeputialis 0–10 E,S,P 0.6 x x x x x xNotes:temporally extinctcommon <strong>and</strong> widespreadpresent, but patchyrareabsentInformation obtained from H<strong>of</strong>fmann & Santelices 1997, Santelices 1989, Castilla et al. 2000, Zagal & Hermosilla 2001, Sepúlveda et al. 2003a,b <strong>and</strong> Hernández et al. 2001.237
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