Macrocystis Integrifolia and Lessonia Trabeculata (Laminariales; Phaeophyceae) Kelp Habitat Structures and Associated Macrobenthic Community Ov Northern Chile
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Helgol Mar Res (2008) 62 (Suppl 1):S33–S43 DOI 10.1007/s10152-007-0096-1 ORIGINAL ARTICLE Macrocystis integrifolia and Lessonia trabeculata (Laminariales; Phaeophyceae) kelp habitat structures and associated macrobenthic community oV northern Chile Mario J. Villegas · Jürgen Laudien · Walter Sielfeld · Wolf E. Arntz Received: 6 June 2007 / Revised: 2 November 2007 / Accepted: 9 November 2007 / Published online: 20 December 2007 © Springer-Verlag and AWI 2007 Abstract Macrocystis integrifolia and Lessonia trabecu- present on barren ground are shorter and have more stipes lata form vast kelp beds providing a three-dimensional habi- compared with those in the dense L. trabeculata kelp bed. tat for a diverse invertebrate and Wsh fauna oV northern Thus, the habitats provide diVerent three-dimensional struc- Chile. Habitat modiWcations caused by the El Niño Southern tures. The associated macrobenthic communities show a Oscillation (ENSO) are likely to alter the inhabiting commu- variable degree of overlapping; however, key faunal assem- nities. The aim of this study was to reveal relationships blages were distinguished for each habitat. Our study pro- between distinct habitat structures of a M. integrifolia kelp vides evidence that habitat diversity drives species diversity, bed, a dense L. trabeculata kelp bed and L. trabeculata the more homogeneous, monospeciWcally composed kelp patches colonizing a barren ground, and the associated dom- bed habitats show comparatively low diversity, mainly inant macrobenthic key species. Seasonally 15 sampling caused by the dominance of the ascidian P. chilensis and T. units (10 m2 each) of any of the three habitats were moni- tridentata in the M. integrifolia bed, and the mussel A. ater tored by SCUBA divers, which counted sporophytes and only present in the L. trabeculata bed. Species richness and macroinvertebrates living between the latter. Furthermore, diversity is highest in the heterogeneous habitat where L. samples of plants were analysed in the laboratory to measure trabeculata patches interrupt the barren ground. Our study the morphological variables: total plant length, maximal revealed morphological diVerences between M. integrifolia holdfast diameter, stipe number, number of dichotomies per and L. trabeculata kelp beds reXected in stipe number, plant stipe, frond width and total drained wet mass. Multivariate length, dichotomies per stipe, and wet mass, which inXuence analysis showed that the L. trabeculata kelp bed is denser, the composition of the associated characteristic fauna and its with a higher number of dichotomies per stipe, whereas functional relations i.e. T. niger and T. tridentata. sporophytes of M. integrifolia are longer with more stipes and wider fronds. Sporophytes of L. trabeculata patchily Keywords Habitat structure · Lessonia trabeculata · Macrobenthic community · Macrocystis integrifolia · Communicated by Sven Thatje. Predator–herbivore–kelp interactions Special Issue: Climate variability and El Niño Southern Oscillation: implications for natural coastal resources and management. S. Thatje (ed.) Introduction M. J. Villegas (&) · W. Sielfeld Departamento de Ciencias del Mar, Universidad Arturo Prat, Casilla 121, Iquique, Chile The kelp Macrocystis integrifolia Bory 1826 and Lessonia e-mail: [email protected] trabeculata Villouta & Santelices 1986 are the two charac- teristic species of Laminariales in shallow hard-bottom J. Laudien · W. E. Arntz habitats oV northern Chile. Both species have biphasic het- Alfred Wegener Institute for Polar and Marine Research, P.O. Box 120161, 27515 Bremerhaven, Germany eromorphic life cycles, with a short-lived microscopic e-mail: [email protected] gametophytic generation alternating with a long-lived mac- V W. E. Arntz roscopic perennial sporophytic generation (Ho man and e-mail: [email protected] Santelices 1997; Buschmann et al. 2004; Tala et al. 2004). 123 S34 Helgol Mar Res (2008) 62 (Suppl 1):S33–S43 They form vast kelp beds that provide a three-dimensional stated that distinct morphotypes may alter the associated habitat structure inhabited by a diverse invertebrate and Wsh invertebrate and Wsh assemblages (Vásquez 1991). fauna (Vásquez 1992; Vásquez et al. 2001; Sielfeld et al. Our study aims to relate diVerent habitat structures of a 2002; Vega et al. 2005; Pérez 2006). The structure of these M. integrifolia kelp bed, a dense L. trabeculata kelp bed kelp beds is physically controlled by variations in upwell- and patchily distributed L. trabeculata colonizing barren ing and alternating oceanographic events such as El Niño ground with the associated benthic macroinvertebrate com- (EN) and La Niña (LN)—the warm and cold phase of the El munity, focussing on key species, which possibly modulate Niño Southern Oscillation (ENSO) (Vásquez and Vega predator–herbivore–kelp interactions, such as sea urchins 2004; Arntz et al. 2006; Vásquez et al. 2006). During El and sea stars. Niño (e.g. 1997/98) mass mortalities of kelp and benthic carnivores such as sea stars were recorded and related to the high coastal water temperatures oV Peru (16°S) (Fernández Materials and methods et al. 1999). In contrast, mass mortalities were not reported from northern Chile (24°S) during EN 1997/98, but during Study site LN 1999 due to elevated abundances of the grazing black sea urchin Tetrapygus niger (Vega et al. 2005) and over- The study was conducted in Chipana (21°S 71°W), located grazing, which resulted in areas without the former kelp, 170 km south of Iquique city (northern Chile) (Fig. 1). The called “barren ground”. The latter is dominated by sea area is a coastal upwelling site (Fuenzalida 1992; Palma urchins and calcareous crustose red algae (Vásquez 1992). et al. 2006), composed of a 4 km long sandy bay exposed to Constant sea urchin grazing may alter sporophyte mor- the northwest with some shallow rocky areas. The latter phology, and thus modulate the habitat structure available provide substrate for extended kelp beds composed mono- for macrozoobenthic and Wsh communities (Vásquez and speciWcally of either L. trabeculata or M. integrifolia. Vega 2004). Two morphotypes of L. trabeculata have been Three diVerent habitats, a M. integrifolia kelp bed, a dense described: (1) a shrub form, with the total mass distributed L. trabeculata bed, and L. trabeculata patches colonizing a among many stipes with high Xexibility and (2) an arbores- barren ground were studied (Fig. 1). cent form, where the total mass is allocated to only very few stipes with limited Xexibility (Vásquez 1992; Vásquez Habitat features and macroinvertebrate communities 1993a). The shrub form is favoured by minor grazing due to high plant abundances and a strong whiplash eVect on herbi- Seasonal sampling was carried out between spring 2005 and vores (Vásquez 1992; Vásquez and Buschmann 1997). In winter 2006, always choosing days with calm sea condi- contrast, wave action and currents selectively aVect the tions. A total of 60 independent sampling units (10 m £ 1m arborescent form, as its lower Xexibility causes a higher each, separated by ¸17 m) located along three replicated chance of dislodgement (Vásquez and Buschmann 1997). transects (Wve replicates per transect) for each habitat were For M. integrifolia diVerences in the blade morphology have assessed. Within sampling units the same SCUBA diver been related to wave exposure (Hurd et al. 1997). It has been counted all sporophytes of M. integrifolia and L. trabeculata Fig. 1 Map showing the loca- tion of the studied (open square) Macrocystis integrifolia kelp bed, the (open inverted triangle) Lessonia trabeculata kelp bed and (open triangle) L. trabecula- ta patches on the barren ground oV Chipana (northern Chile) 123 Helgol Mar Res (2008) 62 (Suppl 1):S33–S43 S35 present. Sporophytes with a single holdfast or an evident bare rock (51%), boulders (17%) and sand (31%). Sporo- fusion, which did not allow discriminate one holdfast from phyte densities also showed signiWcant diVerences (Krus- the other by underwater observation, were considered as kal–Wallis test H2,175 = 11.8, P < 0.05) between the three individual plants. Depth and substrate type were recorded as habitats. The L. trabeculata bed provided higher abundances “bare rock”, “boulder”, and “sand” dominated following (40.0 § 18.0 individuals 10 m¡2) compared to the M. integ- Godoy (2000). Furthermore, the visible macroscopic epi- rifolia bed (29.9 § 23.1 individuals 10 m¡2) and the L. tra- fauna was counted in situ from squares (1 m £ 1 m each, beculata patches (28.1 § 25.0 individuals 10 m¡2). n = 180) haphazardly placed on the substratum between Morphological variables of macroalgae signiWcantly individual sporophytes. Total values were standardized to diVered between habitats; Individual M. integrifolia and 10 m2. Additionally, a total of 36 sporophytes (9 per sam- plants of the dense L. trabeculata bed have a dissimilar pling day) were collected and analysed in the laboratory to stipe number (Kruskal–Wallis test, H2,98 =25.7, P <0.01), individually measure total plant length, maximal holdfast number of dichotomies per stipe (Kruskal–Wallis test, diameter, stipe number, number of dichotomies per stipe, H2,68 =32.5, P < 0.01), frond width (Kruskal–Wallis test frond width and total drained wet mass. H2,98 =24.3, P < 0.01) and total plant length (H2,98 = 53.6, P <0.01) (Fig. 2a–d). No signiWcant diVerence was found Statistical analysis for maximum holdfast diameter (Kruskal–Wallis test, H2,98 =0.71, P = 0.72) and wet mass (Kruskal–Wallis test Since