Species composition, abundance and spatial distribution of coastal fish in relation to the habitat structure of north Chilean kelp beds

jlaudien [ at ] awi-bremerhaven.de


Shallow subtidal hard-bottom communities of northern Chile are dominated by two kelp species, Macrocystis integrifolia Bory 1826 and Lessonia trabeculata Villouta and Santielices 1986. Structure and organization of the kelp communities are controlled by local upwelling processes and ENSO, resulting in alternative habitats such as Macrocystis integrifolia kelp beds, Lessonia trabeculata kelp beds, and barren ground (Vasquez 1992, Vega et al. 2005). We hypothesise that these alternative habitats provide dissimilar structures and thus maintain different abundance, composition and spatial distributions of fish species. In addition, the fish assemblages associated to the three habitats may show different trophic relationships in M. integrifolia and L. trabeculata.Seasonally fifteen sampling units (10 m2) of each studied habitat were assessed using SCUBA diving, to record sporophyte density, fish composition and abundance. The spatial distribution of the fish species was categorized in rock, macroalgae, water column, and sand. The fish community was classified as resident species, which are present throughout the year, seasonal visitors, which are present seasonally, and occasional species, which show no seasonal pattern of occurrence, but cannot be found throughout the year. Macroinvertebrates were counted in 45 haphazardly placed squares of 1 m2. In addition, nine sporophytes of each kelp type were collected and transported to the laboratory for individual estimations of i) total plant length, ii) maximal holdfast diameter, iii) stipes number, iv) phylloid width and v) total drained wet mass.The first results show that M. integrifolia and L. trabeculata kelp beds provide a different habitat structures. Although no significant differences in kelp densities were found between the three studied habitats, M. integrifolia plants are longer and produce more stipes as well as wider phylloids. The comparison between insular L. trabeculata plants from barren ground habitats and those in L. trabeculata kelp beds, revealed that the latter are longer but did not show any further differences.A total of 16 fish species was recorded in the three habitats. The fish assemblage was composed of four resident species in the M. integrifolia and barren grounds habitats, while six resident species were found in L. trabeculata beds. Three seasonal visitors were recorded in M. integrifolia and L. trabeculata, in contrast to the six seasonal species on barren grounds. Nu-merically dominant species were Isacia conceptionis and Chromis crusma in the M. integrifolia habitat. I. conceptionis and Cheilodactylus variegatus were abundant in the L. trabeculata habitat, whereas Scartichthys sp. abounded in the barren ground habitat. We did not find differences between the fish abundances in the studied habitats. However, the significant dissimilar spatial distribution suggests a clear habitat effect (shelter to avoid predators).Dominating key macroinvertebrates present in the three studied habitats were the echinoderms Tetrapygus niger, Loxechinus albus, Heliasther helianthus, and Luidia magellanica, while the bivalve Aulacomya ater only dominated in L. trabeculata kelp beds. T. niger and L. albus were significantly more abundant on barren grounds and did not show differences between M. integrifolia and L. trabeculata beds. In the case of the sea stars, H. helianthus was abundant in M. integrifolia, whereas L. magellanica did not show differences between the studied habitats.Seasonal series patterns on all levels are analysed, integrating morphological features of the macroalgal plants and physical factors. Based on the first results, further in situ experiments were designed in order to analyse the effect of specific features of the kelp on the fish community.

Item Type
Conference (Talk)
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Event Details
CENSOR Midterm Symposium, 4.-8. Sept., Concepción, Chile..
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Villegas, M. , Laudien, J. , Sielfeld, W. and Arntz, W. (2006): Species composition, abundance and spatial distribution of coastal fish in relation to the habitat structure of north Chilean kelp beds , CENSOR Midterm Symposium, 4.-8. Sept., Concepción, Chile. .

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