Abstract
Macrocystis pyrifera kelp beds play a significant ecological role along the coast of Chile. Besides their importance as food, protection structures, substrata, microhabitats and nurseries, regularly occurring natural disturbances (e.g. extremes of the climate variability El Niño–Southern Oscillation) and increased kelp exploitation affect these habitats. The present study aimed to test the dependence of reef fishes on Macrocystis pyrifera and to evaluate the effect of an enhanced habitat structure (experimental M. pyrifera bed) on the abundance, composition and spatial distribution on rock, on macroalgae, in the water column and on sand of the reef fish community. Boulders colonised by M. pyrifera were transported into three replicated experimental areas (9 m2 each) located in a barren ground area. Three barren ground areas (9 m2 each) without manipulation were selected as controls. The fish abundance, composition and spatial distribution on rock, on macroalgae, in the water column and on sand were recorded weekly by scuba diving over a period of 3 months, between 15 February 2007 and 13 June 2007 (4 months). Results indicate significantly higher abundances (mean = 225%) of fishes in the forested areas compared to the barren ground controls (mean = 3.71 fishes/9 m2 and 1.14 fishes/9 m2, respectively). Scartichthys gigas/viridis, Chromis crusma, Cheilodactylus variegatus and Isacia conceptionis numerically dominated the fish assemblages of the experimental kelp patches. Each fish species revealed different distributions in the forested areas: Scartichthys gigas/viridis was more abundant on rocks and C. variegatus in the macroalgae, whereas C. crusma and I. conceptionis preferred the water column above the experimental kelp bed. During the experimental time, the kelp lost some blades and some plants became detached. The overall number of fishes correlated with the declining kelp abundance (r = 0.964, p < 0.05). The fish species showed different responses to these changes in the experimental areas: C. variegatus and I. conceptionis declined in abundance, whereas the abundance of Scartichthys gigas/viridis remained constant.
Highlights
The giant kelp Macrocystis pyrifera (Linnaeus) C
A total of six fish species (Perciformes, Actinopterygii) from six families was present during the study period, with five species occurring at the control plots and all six at the forested plots
Fish community composition and diversity related to forested versus control plots In temperate regions, reef fishes are frequently associated with macroalgae (e.g. Holbrook et al 1990; Levin and Hay 1996; Pérez-Matus et al 2007, 2012; Sielfeld et al 2010; Miller et al 2018; Witman and Lamb 2018)
Summary
The giant kelp Macrocystis pyrifera (Linnaeus) C. Agardh 1820, (synonym Macrocystis integrifolia Bory) is a characterising macroalga of shallow hard-bottom habitats off northern Chile (Dayton 1985; Vásquez 1992; Steneck et al 2002; Villegas et al 2008; Stotz et al 2016). Most of the forest fishes are plastic in their feeding preference along the coastline (Pérez-Matus et al 2012) and a recent study from a northern Chilean kelp bed indicates that the invertebrate community structure does not strongly differ between alternative habitats (Villegas et al submitted)
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