ORIGINAL ARTICLE Influence of disturbance and nutrient enrichment on early successional fouling communities in an oligotrophic marine system Joa ˜ o Canning-Clode 1,2 , Manfred Kaufmann 2 , Markus Molis 3 , Martin Wahl 1 & Mark Lenz 1 1 Leibniz Institute of Marine Sciences, University of Kiel, Kiel, Germany 2 Department of Biology & Centre of Macaronesian Studies, University of Madeira, Funchal, Madeira Island, Portugal 3 Biologische Anstalt Helgoland, Foundation Alfred-Wegener-Institute for Polar and Marine Research, Kurpromenade, Helgoland Problem Since several decades, most ecosystems experience a rapid loss of biodiversity (e.g. Hooper et al. 2005). This process is observable at both local and global spatial scales, and at organisational levels from genomes to landscapes (Sala & Knowlton 2006). While the ongoing loss of biodiversity is not questioned, the significance of the loss, i.e. the eco- logical role of diversity, was debated for years. Meanwhile, apart from ethical considerations, the value of taxonomic and functional diversity for ecosystem services and com- munity stability is postulated theoretically and frequently found experimentally (e.g. Loreau et al. 2001; Giller et al. 2004; Balvanera et al. 2006). The heterogeneous distribu- tion of diversity at different scales in space and in time has incited the formulation of explanatory models over the last decades (Connell 1978; Huston 1994; Hubbell 2001). Two factors which have frequently been suggested to control diversity, are disturbance (Connell 1978; Sousa 1979) and system productivity (Huston 1979; Berendse 1993). Disturbance is considered a relatively discrete event in time that removes biomass, liberates resources, inter- rupts succession and facilitates the establishment of new individuals (from Grime 1977; Sousa 1984; White & Pick- ett 1985). ‘Productivity’ is a somewhat vaguer concept, which alternately has been used in the sense of annual primary production, site fertility, larval settlement rate, or nutrient availability (e.g. Menge & Sutherland 1987; Ber- endse 1993; Allcock & Hik 2003; Gessner et al. 2004). The most widely accepted model linking disturbance and diversity, as formulated in the Intermediate Disturbance Hypothesis (IDH, Connell 1978), postulates a unimodal relationship with maximum diversity at ‘intermediate’ levels of disturbance. Such a pattern is, however, only one of a variety of diversity–disturbance relationships found in nature (Mackey & Currie 2001). The relationship between productivity and diversity seems to be similarly complex and variable (Waide et al. 1999; Mittelbach et al. Keywords Disturbance; diversity; fouling; Madeira Island; multiple stressors; nutrient enrichment; productivity. Correspondence Joa ˜ o Canning-Clode, Leibniz Institute of Marine Sciences, University of Kiel, Duesternbrooker Weg 20, 24105 Kiel, Germany. E-mail: jcanning-clode@ifm-geomar.de Accepted: 12 November 2007 doi:10.1111/j.1439-0485.2007.00210.x Abstract Disturbance and productivity are often cited as the main factors determining temporal and spatial patterns in species distribution and the diversity of com- munities. A field experiment was conducted to test the role of these factors in the structuring of early successional fouling communities in a nutrient limited system at the south coast of Madeira Island. Macro-benthic sessile communi- ties, established on artificial settlement substrata, were manipulated and sur- veyed over a 9-week period. We applied mechanical disturbances of four different frequencies crossed with three levels of inorganic nutrient enrichment. Fertilization enhanced community diversity by favouring the establishment and growth of macroalgae. Disturbance reduced diversity by eliminating species – but only at the highest nutrient level. This is explained by a multiple-stressor model; species most sensitive to nutrient deficiency (only present in the highest enrichment treatment) were simultaneously the most sensitive to disturbance. Marine Ecology. ISSN 0173-9565 Marine Ecology 29 (2008) 115–124 ª 2008 The Authors. Journal compilation ª 2008 Blackwell Publishing Ltd 115