Effects of physical ecosystem engineering and herbivory on intertidal community structure

Abstract

Physical ecosystem engineers play dominant roles in a wide variety of communities. While many of the direct, positive effects of ecosystem engineers are readily apparent, the roles of engineers are often mediated by indirect interactions stemming from the facilitation of one or a few key species. Although direct and indirect effects are both critical drivers of community dynamics, they are rarely considered together with regards to ecosystem engineering. In the present study barnacle and herbivorous gastropod densities are experimentally manipulated to investigate the direct positive effects of habitat provision by barnacles as well as indirect effects mediated by molluscan grazers. Molluscan grazers (Littorina spp.) and herbivorous arthropods were positively influenced by the presence of barnacles. Arthropod abundance and species richness were lower when Littorina spp. were present. This pattern was not influenced by barnacle cover, suggesting that competition among herbivore functional groups was strong but independent of biogenic habitat complexity. In addition, Littorina spp. had strong negative effects on the filamentous alga Urospora penicilliformis, but this effect was only seen in the absence of barnacles. Finally, Littorina spp. reduced the recruitment of the principal habitat-forming barnacle Balanus glandula, suggesting that Littorina spp. may mediate a negative feedback loop in B. glandula population dynamics. Given the ubiquity of ecosystem engineers, similar combinations of direct and indirect influences may have far-reaching consequences for community dynamics and species richness in a wide range of systems.

Non-linear density-dependent effects of an intertidal ecosystem engineer

“…Maximizing empty test availability does come at the expense of B. glandula density relative to scenarios with lower levels of predation. Live barnacles such as B. glandula also provide important habitat structure, and littorine snails and other species are more abundant where live barnacle cover is higher (Harley 2006). However, our long-term N. ostrina exclusion experiment indicates that losses in B. glandula may be balanced by increasing cover of the competitively inferior C. dalli (see also Dayton 1971).…”

“…Examples of this can be found in a wide variety of ecosystems, both terrestrial and aquatic (for review, see Jones et al 1994Jones et al , 1997. Autogenic ecosystem engineers are frequently important on rocky intertidal shores, where organisms such as sessile invertebrates and canopy-forming algae can ameliorate extremes in thermal stress, desiccation stress, and hydrodynamic forces for a variety of matrix-dwelling and subcanopy species (Seed and Suchanek 1992;Bertness et al 1999;Castilla et al 2004;Harley 2006). Allogenic engineers are also important; various species (e.g., sea urchins) create pits and boreholes in the rock, which can then be used by additional species (Schoppe and Werding 1996).…”

Cool barnacles: Do common biogenic structures enhance or retard rates of deterioration of intertidal rocks and concrete?

“…Tests remain affixed to the surface after the organism dies (and may persist for several months and years) making them particularly practical targets for a laboratory study. Furthermore, the establishment of barnacles is an important early step in the development of diverse benthic communities (Farrell, 1991;Harley, 2006;Tews et al, 2004;Thompson et al, 1996), and there is considerable opportunity to facilitate their settlement and recruitment to engineered surfaces (for ecological gain) using simple textural manipulation (Coombes et al, 2015a). The influence of barnacles on deterioration processes, such as thermal degradation and salt weathering, is therefore an important question we aimed to address.…”

“…Implications for ecology and ecological engineering at the coast Biological structures have facilitative ecological roles by alleviating thermal and desiccation stresses for other species (e.g., Harley, 2006). The thermal biology of rocky shore species has received growing research interest (Carwright and Williams, 2014;Harley, 2013), yet the two-way feedbacks between epibiota, substrate thermal properties and near-surface microclimates have gained only limited attention (see Denny and Harley, 2006;Gedan et al, 2011;Miller et al, 2009).…”

Habitat complexity and community composition: relationships between different ecosystem engineers and the associated macroinvertebrate assemblages

“…Different species of cordgrass, mussels, and barnacles have been reported to alter light, temperature, wave action, sedimentation, and food availability, which in turns have influenced with the abundance and distribution of invertebrate fauna (e.g. cordgrass: Capehart and Hackney 1989;Netto and Lana 1999;Hedge and Kriwokwen 2000;Bortolus et al 2002;mussels: Thiel and Ullrich 2002;Adami et al 2004;Prado and Castilla 2006;barnacles: Bros 1980;Barnes 2000;Harley 2006). However, the differences on the amount of structural components of these ecosystem engineers species supply three contrasting natural scenarios with increasing habitat complexity (from high to low: cordgrass-mussel-engineered, musselengineered, and barnacle-engineered habitats) that allow us to address the following questions: How different is a macroinvertebrate assemblage when dominated by different ecosystem engineers?…”