the humboldt current system of northern and central chile - figema

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MARTIN THIEL ET AL.p. 240ff.). Durvillaea antarctica does not extend further north than 32°S. Patches or belts formedin the low intertidal zone by Lessonia nigrescens and Durvillaea antarctica generally have extentsof several square metres up to >100 m 2 . Subtidal kelp forests of Lessonia trabeculata and Macrocystisspp. may extend over >1000 m 2 , comprising some of the largest habitat patches formed byEEs. Distances between neighbouring patches are small in the case of Lessonia spp. and Durvillaeaantarctica but individual forests of Macrocystis spp. can be separated by several hundred kilometres(see also Kelp forests, p. 240ff.). Persistence of patches over time may be favoured by recruitmentof new sporophytes into existing kelp patches (Santelices & Ojeda 1984).Turf algae generally form smaller patches, with individual patches rarely exceeding an area ofa few square metres. Corallina officinalis and Gelidium chilense (and other turf algae, e.g., Montemariahorridula, Rhodymenia skottsbergii) form long-lived patches in the intertidal zone (López& Stotz 1997, Vásquez & Vega 2004a, Wieters 2005), and distances between neighbouring patchesare relatively small (Table 3). Glossophora kunthii, Halopteris funicularis, Asparagopsis armata(and others, including Corallina officinalis) occur mainly on shallow subtidal hard bottoms wherethey form patches of several square metres and, while thalli may disappear during the winter, thestolons persist over several years (Vásquez et al. 2001a). Patches may extend their size or renewthalli via asexual proliferation.The polychaete Phragmatopoma moerchi forms patches of several square metres in extent inthe low intertidal and shallow subtidal zone in areas with a high supply of sand and shell fragments(Sepúlveda et al. 2003b). These patches persist over several years, but disappear if renewal isreduced, either due to low larval supply or high postsettlement mortality (Zamorano et al. 1995).The barnacle Austromegabalanus psittacus forms aggregations in the low intertidal and shallowsubtidal zone; patches generally are small, rarely exceeding more than a few square metres in area.This species occurs all along the coast of northern and central Chile and little is known about thetemporal dynamics of individual patches. Bivalves form extensive patches of a few square metresup to >1000 m 2 in area in the mid-intertidal (Perumytilus purpuratus), low intertidal (Semimytilusalgosus) and subtidal zones (Choromytilus chorus, Aulacomya ater). In the absence of predatorspatches can persist over many years (Durán & Castilla 1989), facilitated by regular recruitmentinto adult patches (Alvarado & Castilla 1996). Most bivalve species have a wide latitudinaldistribution, but Perumytilus purpuratus and Aulacomya ater are almost entirely absent over anextensive area in northern Chile between 23°S and 32°S (Fernández et al. 2000, personal observations),which appears to be mainly due to limited larval supply in that region (for Perumytiluspurpuratus see Navarrete et al. 2005). The ascidian Pyura chilensis occurs in small patches in theshallow subtidal zone (e.g., Vásquez & Vega 2004b), while the congener P. praeputialis formsextensive belts in the low intertidal zone (Table 3). Patches of P. chilensis persist over many years atthe same location (personal observations), but little is known about the population dynamics withinpatches. In P. praeputialis, recruitment may be most successful in the vicinity of adults (Clarkeet al. 1999), thereby favouring the long-term persistence of patches. While P. chilensis has a widegeographic distribution, P. praeputialis is restricted to a small range of 70 km along the Bay ofAntofagasta (23°S) in northern Chile (Castilla et al. 2000).Macrofauna associated with ecosystem engineers on hard bottomsA wide diversity of organisms is associated with habitat-forming species on hard bottoms ofnorthern and central Chile. Highest species richness is found in the kelp holdfasts, intermediatenumbers of associated species are reported from ascidian and bivalve reefs, and turf algae harbourfewest species of associated macrofauna (Figure 13A). This relationship appears to be related to238
THE HUMBOLDT CURRENT SYSTEM OF NORTHERN AND CENTRAL CHILE140120120100Species richness10080604080604020200Lessonia trabeculataLessonia nigrescensMacrocystis integrifoliaMacrocystis integrifoliaDurvillaea antarcticaHalopteris funicularisCorallina officinalisGelidium chilensePhragmatopoma moerchiPerumytilus purpuratusPerumytilus purpuratusPyrua praeputialis01 to 10 10 to 1000 >1000Patch size (m 2 )BKelps Turf algae Suspension feedersAFigure 13 (A) Species richness of macroinvertebrates associated with habitat-forming macroalgae or suspensionfeeders from intertidal and subtidal hard bottoms of the northern and central coast of Chile; for reasonsof comparability only studies that reported at least seven phyla of associated macrofauna were considered.(B) Average species richness in biotic habitats of different patch sizes; information obtained from López &Stotz 1997, Gelcich 1999, Godoy 2000, Thiel & Vásquez 2000, Cáceres 2001, Cerda & Castilla 2001,Hernández et al. 2001, Vásquez et al. 2001b, Thiel & Ullrich 2002, Sepúlveda et al. 2003a,b, Prado & Castilla 2006.the fact that kelp beds and ascidian and bivalve reefs have a comparatively large spatial extentwhile patches of turf algae rarely cover more than a few square metres (Figure 13B). A positiverelationship between patch size and number of associated species has been revealed for most habitatformingspecies (Vásquez & Santelices 1984, Villouta & Santelices 1984, Thiel & Vásquez 2000,Hernández et al. 2001, Sepúlveda et al. 2003a,b).Several macrofauna species have been reported from a variety of different biotic habitats. Of251 species identified from biotic substrata (see references in Figure 13), 11.6% have been foundin all three types of main biotic habitats (kelps, turf algae and suspension feeder reefs), 23.5% havebeen found in two types and 64.9% are only reported from one type of habitat. It must be emphasisedthat so far no single study has compared the associated fauna among the three main types of EEs,and there is little indication that there are habitat specialists that only occur in one type of bioticsubstratum. For example, Hernández et al. (2001) emphasise that several of the polychaetes foundin patches of the barnacle Austromegabalanus psittacus also occur in other habitats. Similarly,Sepúlveda et al. (2003b) mention that many species from surrounding habitats associate with thereef-building polychaetes Phragmatopoma moerchi. They also emphasise that these biotic substratamay serve as recruitment habitat for some organisms. Similar observations led López & Stotz(1997), who found juvenile stages of many crustaceans and molluscs in Corallina officinalis, to239
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