Establishment and persistence of species-rich patches in a species-poor landscape: role of a structure-forming subtidal barnacle

Abstract

Some sessile invertebrates are capable of maintaining space in barren habitats produced by sea urchins, thereby creating species-rich patches in a species-poor landscape. We sought to determine the role of a large and common barnacle, Austrobalanus imperator, in the establishment and persistence of these species-rich patches. Barnacle density was modified in 2 experiments at sites in southeastern Australia. The first experiment concerned community establishment and involved the addition of barnacles in 4 densities (zero [control], low, medium and high) to plots on vertical rock surfaces. The addition of barnacles at ecologically realistic densities and spatial arrangements rapidly resulted in statistically significant increases in invertebrate cover and diversity. After 56 mo, the diversity of invertebrates was significantly higher on plots that received high densities of barnacles relative to controls. However, invertebrate cover no longer differed between treatment plots, despite evidence that barnacles modify the grazing intensity of sea urchins. The second experiment assessed the persistence of sessile invertebrates following the removal of barnacles from wellestablished assemblages dominated by sponges. The removal of barnacles did not hinder the rapid recovery of sponges to pre-manipulation levels, indicating that barnacles played an inconsequential role in well-established assemblages. We conclude that barnacles play an important functional role in this system, as they promote the recruitment of sessile invertebrates. It was also clear that the development of invertebrate assemblages on natural vertical surfaces was very slow, which raises the question of whether we are examining these important occupiers of space at appropriate temporal and spatial scales.KEY WORDS: Cirripedia · Echinoidea · Grazing activity · Habitat structure · Porifera · Sessile invertebrates · Structural heterogeneity · Rocky subtidal zone Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 380: [187][188][189][190][191][192][193][194][195][196][197][198] 2009 while it may also influence the structure and dynamics of assemblages (Lawton 1983, Downing 1986, Williamson & Lawton 1991. For sessile benthic invertebrates the nature of the substratum, such as surface rugosity, can be an important determinant of patterns of settlement and post-settlement survivorship (Dean & Hurd 1980, Dean 1981, Keough & Downes 1982, Sebens 1991, Walters & Wethey 1991, Walters 1992, Guichard & Bourget 1998. Superimposed on these patterns is the biogenic structure imparted by the biota, which may modify patterns of settlement and survivorship, often via the creation of refugia (Russ 1980, Witman 1985, Littler et al. 1986, Davis 1987, 1996 or by changing hydrodynamic conditions (Eckman 1983, Littler et al. 1983, Walters et al. 1999.The impact of sea urchins on the distribution and abundance of macroalgae is well established in subtidal community ecology (Lawrence 1975). The grazing activities of urchins...

Role of the sea anemone Metridium senile in structuring a developing subtidal fouling community

“…Through removal experiments, Sutherland (1978) showed that the presence of the bryozoan Schizoporella unicornis and the ascidian Styela plicata led to the formation of previously observed 'multiple stable points' during succession (Sutherland 1974). Similarly, Blum et al (2007) showed that the presence of the invasive ascidian Ciona intestinalis dominated space and depressed species richness, while Davis & Ward (2009) showed that the presence of the barnacle Austrobalanus imperator is essential in the formation of a species rich community by promoting the recruitment of other sessile invertebrates. Still other studies have used addition and removal experiments to demonstrate lowered diversity by the blue mussel Mytilus edulis (Durr & Wahl 2004), recruitment facilitation among the ascidians Pyura spinifera and Cnemidocarpa pedata (Davis 1996), and reduced settlement due to the presence of 4 different species of resident ascidians (Osman & Whitlatch 1995).…”