Assembly and maintenance of subtidal habitat heterogeneity: synergistic effects of light penetration and sedimentation

Loss of fucoid algae along a gradient of urbanisation, and structure of benthic assemblages

“…Conversely, canopies of Cystoseira compressa did not seem to exert such a strong effect on understorey species and were less effective in preventing colonisation by C. elongata. Algal turfs, including those originated by C. elongata have been suggested to inhibit the recruitment of many canopy-forming algae (Kennelly 1987, Airoldi 1998, Connell 2005. Although the concept of alternate stability is controversial (Scheffer et al 2001 and references therein), turfs of corallinales and canopy algae have been proposed as alternative states in temperate reefs (Airoldi 2003, Connell 2005; this study supports the hypothesis that coastal urbanisation could be a driver of shifts between canopy habitats and turfs.…”

“…Algal turfs, including those originated by C. elongata have been suggested to inhibit the recruitment of many canopy-forming algae (Kennelly 1987, Airoldi 1998, Connell 2005. Although the concept of alternate stability is controversial (Scheffer et al 2001 and references therein), turfs of corallinales and canopy algae have been proposed as alternative states in temperate reefs (Airoldi 2003, Connell 2005; this study supports the hypothesis that coastal urbanisation could be a driver of shifts between canopy habitats and turfs. Science and management demand simplified representation of complex systems, but such simplification depends on correct understanding of natural history (Dayton & Sala 2001, Dayton 2003.…”

Effects of mean intensity and temporal variance of sediment scouring events on assemblages of rocky shores

“…These results are in agreement with those of Kendrick (1991) who found a lower number of species on boulders subjected to treatments of erosion and scouring by sediment than on unmanipulated ones. The mechanisms proposed to explain negative effects on diversity include inhibition of recruitment (Devinny & Volse 1978), direct scour of species (Kendrick 1991, Airoldi 1998 quent switches in dominance of species (Connell 2005). Intensity and temporal variance of disturbance were not the only processes driving the observed patterns in the data.…”

“…Strong waves remove organisms from the substratum, opening gaps (Benedetti-Cecchi 2000) in which patterns of recovery may be affected by interactive effects of sediment and wave action through different mechanisms including inhibition of settlement, smothering and abrasion of recently settled propagules and direct elimination of less tolerant species (Vadas et al 1992). Sediment may also have positive effects on sessile organisms, by preventing the monopolisation of space by competitively dominant species (Airoldi 2003), increasing local levels of nutrients or providing protection from other sources of disturbance (Taylor & Littler 1982, Littler et al 1983, McQuaid & Dower 1990, Gorgula & Connell 2004, Connell 2005.…”

Can strong consumer and producer effects be reconciled to better forecast ‘catastrophic’ phase-shifts in marine ecosystems?

“…Ephemeral algae, such as turfs, for example, are not usually competitively superior to perennial habitat formers, but can smother seagrasses (Duarte, 2002) and be competitively superior to the early life-history stages of recruiting corals (Birrell et al, 2005;Arnold et al, 2010) and kelps ). They are frequently the primary space occupiers after disturbances such as mass-bleaching events and regional out-breaks of crown-of-thorns starfish on coral reefs (Diaz-Pulido et al, 2002), and storms in kelp forests (Connell, 2005). Even in the absence of major perturbation, rates of mortality of corals and kelps are often high (corals Hughes et al, 1985;kelps Hatcher et al, 1987).…”